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Po401 Replaced all vacuum lines, egr valve, egr contol

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Po401 Replaced all vacuum lines, egr...
Po401
Replaced all vacuum lines, egr valve, egr contol solenoid, map sensor, complete tune up, pcv valve, plenum, cleaned all deposits on intake, exhaust, and pioes, checked all wiring for shorts.
Code still comes up after short drive cycle. What gives?
01 impala, 3.8
Submitted: 9 months ago.Category: Chevy
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Answered in 2 minutes by:
9/17/2017
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago
AMEDEE
AMEDEE, CHEVY TECHNICIAN
Category: Chevy
Satisfied Customers: 28,006
Experience: ASE certified tech ADVANCED LEVEL SPECIALIST. Wisconsin certified emissions state inspector
Verified

Hello and welcome!

My name isCustomerand I can assist you with your question.

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Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

I am very sorry your having this issue with your vehicle.

I will try my best to answer all of your questions.

However, before we get started, please let me mention a few things.

1. If at any point you would like to speak on the phone, please feel free to request a phone call on your end and I can call you right away.

2. If you dont understand any technical terms or anything that I mention (component tests or theory or operation), please let me know and I will provide you with a more in debt explanation or answer.

3. Please understand that I am here to help.

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Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

Do you have access to a scanner that can read live data or bi-directional controls?

Are you looking for some possible causes?

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Customer reply replied 9 months ago
I have a innova 1403, i believe it hives live data. Not sure about by directional controls
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

Ok, no problem

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Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

What work was done to the vehicle prior to this code?

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Customer reply replied 9 months ago
Unsure. It came to me with a check engine light on, po404. I did a complete tune up and changed the egr valve. Then it developed a code po401. Over the last two months i have changed the plenum, inspected and replaced all bad cacuum lines, cleaned the intake, replaced numerous sensors,
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

Thank you for that information.

What is the engine vacuum at when the engine is at idle?

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Customer reply replied 9 months ago
I belueve 16.5
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

Can you double check for me please?

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Customer reply replied 9 months ago
Right now it is at a steady 15
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

If you remove the oil cap from the engine while it is running, is there vacuum in the crankcase?

Does the idle fluctuate at all if you remove the oil cap while the engine is at idle?

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Customer reply replied 9 months ago
vacuum drops to 13 when i remove the oil cap
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

Ok, thats the problem. The EGR code will not get resolved until the vacuum in the crankcase issue is fixed.

There should not be much (if any) negative pressure in the crankcase.

13 inches of vacuum is WAY too low.

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Customer reply replied 9 months ago
Ok, explain that to me please. My vacuum drops from 15 to 13 when i remove the oil cap.
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

The PCV valve or system should be separate. The ONLY air or vacuum that SHOULD be in th CRANKcase is the regulated flow that comes through the PCV valve. If there is ANY vacuum leaking into the crankcase for any other reason, it will cause this condition.

Most of the time this is caused by a missing O ring or incorrectly installed PCV valve.

HOwever, it can be also caused by an incorrectly installed intake manifold (plenum)

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Customer reply replied 9 months ago
Ok. On the pcv valve itself should there be an o ring on it or does it simply drop into place
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

There should be an o-ring there, sir.

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Customer reply replied 9 months ago
On the metal pcv valve itself?
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

Yes sir

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Customer reply replied 9 months ago
There already is a large oring on the housing where the cap that holds the map sensor twists on. The oring you mention is seperate from that
Customer reply replied 9 months ago
There already is a large oring on the housing where the cap that holds the map sensor twists on. The oring you mention is seperate from that?
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

YES, there should be another one. I think there is two or maybe even three in total

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Customer reply replied 9 months ago
Are you still there?
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

YES sir

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Customer reply replied 9 months ago
Sorry i did not hear back from you
Customer reply replied 9 months ago
I installed the oring. Taking it on a test drive now.
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

Ok, sounds good

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Customer reply replied 9 months ago
Code po401 came back on.
Customer reply replied 9 months ago
What now?
Customer reply replied 9 months ago
Amadee??
Customer reply replied 9 months ago
Still there?
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

Sorry for the delay!

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Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

YES, still here.

Was working with other customers.

Your next step is to recheck engine vacuum.

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Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

I am waiting for your reply, sir.

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Customer reply replied 9 months ago
I am waiting to try the next suggestion. Please let me know when you are ready.
Thank you
Customer reply replied 9 months ago
I rechecked vacuum. It is at 16 lbs and when i take off the oil cap it drops less than one inch
Customer reply replied 9 months ago
Sorry 16 inches not lbs
Customer reply replied 9 months ago
When i take off the oil cap vacuum doesnt drop at all
Customer reply replied 9 months ago
Are you getting my responses
Customer reply replied 9 months ago
Hello?
Customer reply replied 9 months ago
I dont know if you are busy or if this site is having problems. It says payment error but my card is active and eorks fine everywhere else.
Customer reply replied 9 months ago
You are very knowledgeable, please get back to me so we can finish trouble shooting this isdue
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

Hello and sorry for the delay sir. Was eating dinner with the family.

The payment for the phone call does not go through.

16 inches at idle is not enough. If the crankcase issue is all fixed but the engine vacuum is still low, this still could affect the EGR opertation.

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Customer reply replied 9 months ago
O ok.
Sorry i didnt mean to rush you.
What do i check now for vacuum
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

Most of the time this issue is caused by an air or a vacuum leak. Smoke testing the intake system is the best way to pinpoint a vacuum leak.

Also, is this a new PCV valve? If not, replace it with a new one.

If the code continues to set, clean the carbon from both the Exhaust Gas Recirculation (EGR) intake and exhaust ports. Any carbon in the EGR passageways can cause a reduced flow of EGR gases.

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Customer reply replied 9 months ago
Whst should my vacuum be at idle? It sounds like its sucking air but ive sprayed brake cleaner everywhere and nothing
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

It should be 19 inches of solid steady engine vacuum at idle.

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Customer reply replied 9 months ago
Never done a smoke test. How do i perform that? Ive already cleaned the carbon on both ports and all the tubing
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

This is done using a smoke tester.

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Customer reply replied 9 months ago
Ok i will be in touch
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

Sounds good!

I am glad I can help!

Please don't forget to honor your good faith deposit by rating my answer as "5 STARS or SMILEY FACES" for assisting you today.

Keep in mind, we can still continue this conversation at no further cost to you even after you rate my answer. Just reply back to me using this page and I will get it and get back to you ASAP!

I just ask that you allow time in between replies as I may be helping other customers or off line spending time with the family.

Also, if you are a member or if you have a subscription to the site, you still need to rate my answer in order for me to get credit for assisting you with your question.

You should see the rating system towards the top of the page.

Please let me know if you have any further questions.

Thanks and have a great day!!

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Customer reply replied 9 months ago
What should my vacuum measure?
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

It should be 19 inches of solid steady engine vacuum at idle.

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Customer reply replied 9 months ago
Ok thank you. I will rate you and stay in touch.
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

Sounds good thank you!

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Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

You should see the rating system towards the top of the page.

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Customer reply replied 9 months ago
Good afternoon Amadee,
I'm sorry I work full time and just now got a chance to continue working on this car.
I found the vacuum leak and addressed the issue, I had a poor connection where the brake booster hose connects to the plenum. I now read 22 inches of mercury on my vacuum gauge.
I took the car for a test drive and as usual within 5 miles it threw the po401 code again.
What now?
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago
Send me a picture or video of the engine vacuum reading on the gauge with the engine at idle. Thank you.
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Customer reply replied 9 months ago
Please send me instructions on how to send you a picture.
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

There is a paperclip icon on the toolbar on top of your reply box you can use to upload a pic.

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Customer reply replied 9 months ago
What next
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

Thank you.

Please show me this with it hooked up to the engine showing this reading.

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Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

No sir. Not at all. Customers lie to me all of the time so we can "move onto the next step" yet they did not complete the first step correctly and they wonder why they do not get the desired results.

Thank you for sending the pic. Not that this has been addressed and we know engine vacuum is good, the next step is to check the EGR valve signal. "Desired" vs "actual" to see if there is a difference. This is done reading live data on your scanner.

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Customer reply replied 9 months ago
Ok
Customer reply replied 9 months ago
I dont believe my scanner has egr valve signal
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

Sure it does.

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Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

Thats how the computer knows or "thinks" there is an EGR problem.

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Customer reply replied 9 months ago
Im looking at the live data screen. I dont see anything that says egr
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

Keep looking

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Customer reply replied 9 months ago
We'll have to continue this tomorrow afternoon. I need to be up at 4 a.m. for work. My time is valuable, i hope you wont waste my time tomorrow with fools errands.
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

One thing is for sure, we need to do the tests accurately. :)

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Customer reply replied 9 months ago
I did. You wasted my entire afternoon.
Just so you know I am a heavy equipment mechanic. i repair cranes and excavators all day 6 days a week.
I hired you to help me fix this. I know all about thorough testing.
Goodnight
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

I think you better get some sleep sir.

Talk in the morning.

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Customer reply replied 9 months ago
Thank you for checking in.
I will not have time to work on this car tonight. Hopefully I will be able to get back to it tomorrow. If not then this weekend.
Mel
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

Sounds good Mel,

Thanks for the update!

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Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

Hello there!

I am just checking in to see how things are going and to see if you need any further assistance?

If so, please let me know as I will be happy to help.

Best Regards,

Customer/p>

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Customer reply replied 9 months ago
Customer
I have been working very long hours and have not had time to work on the Impala.
Right now I have about two hours time to trouble shoot as much as I can before I need to leave for work in the morning.
Last we discussed you were asking me what my scanner EGR info was and I was telling you I did not believe my scanner showed EGR position.
Right now I am looking at the information on the live data option of my scanner and the informstion readreads as follows:
LIVE DATA
Fuel Sys 1. OL
Calc LOAD (%) 0
Ect (°C) 24
STFT B1 (%) 0
LTFT B1 (%) -0.7
MAP (kPa) 100
Eng RPM. 0
Veh Speed. (km/h) 0
Spark Adv (°) 0
IAT (°C) 27
MAF. (g/s) 1.34
TPS. (%) 0
Air Status. OFF
O2S. B1. (V) 0.230
STFT. B1. S1 (%) 0
02S B1 S2 (V) 0.065
STFT. B1 S2. (%) NA
OBDSup. OBD2
MIL Dis (km) 0
The vehicle is currently off with the key in the accessory position.My question to you now is which of these displays on my live data if any is my EGR position?
Do I need to locate a different scanner in order to view EGR position and info
so that we can continue to trouble shoot this vehicle?
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

Thank you.

Let me ask, are you plugged in connected to the vehicle through Global OBD2 or did you enter the vehicle VIN to get this information?

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Customer reply replied 9 months ago
I am plugged into the vehicle. But the vehicle is off with the key in the accessory position.
Last we spoke you said the next step was to use my scanner to verify EGR position. Are we still doing that?
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

Ok, then yes, you may need to get your hands on a different scanner that can read live data with the EGR position.

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Customer reply replied 9 months ago
Ok. I will track one down and we can go from there.
Thank you
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

You are most welcome sir

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Customer reply replied 9 months ago
Will you kindly give me instructions on what or how to check the desired vs actual egr signal so that when I have another break in my schedule I can get directly to diagnosing the vehicle?
I will most likely be using my friends snap on solus scanner.
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

YES.

With the engine running, you would look for the EGR "desired" signal and the EGR "actual" signal" and reply back with the readings.

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Customer reply replied 9 months ago
Great. I will keep you posted.
Thank you
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 9 months ago

Your welcome

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Customer reply replied 8 months ago
With the engine running I am not getting any reading for EGR actual. I tried it while at idle, at 1000, 2500, and 3000 rpm's.
I then entered desiref egr position of 20% then 30%. But still there was no value for egr actual value.
What do you think?
I have replaced the valve twice. I have tested all my wires and they appear to have the correct voltages at the egr valve
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 8 months ago

I think maybe the PCM could be faulty.

You could remove the EGR valve, turn the key on and run a self test on the EGR valve using your scanner to see if the pintail moves. If not, we know we are headed in the right direction.

P0401 Insufficient EGR Flow Detected

  • MAP sensor is dirty, damaged or it is "skewed"
  • EGR passages or intake passages clogged or restricted
  • EGR vacuum hoses damaged, loose or routed incorrectly
  • EGR solenoid valve is clogged, damaged or has failed
  • EGR pipe is clogged, dirty or otherwise restricted
  • Base engine problem (restricted exhaust), or any other problem that causes the engine to run poorly

DTC P0401

Circuit Description

The powertrain control module (PCM) tests the EGR system during deceleration by momentarily commanding the EGR valve to open while monitoring the manifold absolute pressure (MAP) sensor signal. When the EGR valve is opened, the PCM should see a proportional increase in MAP. If the expected increase in MAP is not seen, the PCM notes the amount of error that was detected and adjusts an internal fail counter towards a fail threshold level. When the fail counter exceeds the fail threshold level, the PCM will set this DTC. The number of test samples required to accomplish this may vary according to the amount of detected flow error.

Normally, the PCM will only allow one EGR flow test sample to be taken during an ignition cycle. To aid in verifying a repair, the PCM allows 12 test samples during the first ignition cycle following a scan tool Clear Info or a battery disconnect. Between nine and twelve samples should be sufficient for the PCM to determine adequate EGR flow and pass the EGR test.

Conditions for Running the DTC

The System Voltage is between 11–18 volts.

The AC status does not change.

The transaxle range does not change.

The TP angle is less than 1 percent, deceleration.

The intake air temperature is less than 80°C (176°F).

The engine coolant temperature is greater than 75°C (167°F).

The engine speed is between 1100–1400 RPM.

The IAC position is steady.

The vehicle speed is greater than 45 km/h (28 mph) during deceleration.

The BARO sensor greater than 70 kPa (10.1 psi).

The vehicle will need to be driven above 80 km/h (50 mph), and then allowed to decelerate. When the vehicle is decelerating while meeting all of the criteria listed above, the PCM will enable the test to run. As the test is running, you will see the desired EGR parameter and the EGR position sensor on the scan tool change from 0 to a calibrated value above 0.

Conditions for Setting the DTC

MAP changes monitored during EGR flow test indicate insufficient EGR flow.

Action Taken When the DTC Sets

The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.

The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

The PCM disables the EGR valve for the ignition cycle.

Conditions for Clearing the MIL/DTC

The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

Clear the MIL and the DTC with a scan tool.

Diagnostic Aids

IMPORTANT: Inspect for the following conditions:

An EGR valve that shows signs of excessive heat—Check the exhaust system for blockage, or for a plugged catalytic converter. Refer to Restricted Exhaust in Engine Exhaust.

Vacuum restriction to the MAP sensor.

A restriction to the MAP sensor can cause the EGR flow test to fail due to insufficient MAP changes being monitored during the test.

An engine that is running poorly may cause this DTC to set.

Poor connections or a damaged harness.

Inspect the wiring harness for damage.

If the harness appears to be OK, observe the EGR Position Sensor display on the scan tool while moving connectors and wiring harnesses related to the EGR valve. A change in the display indicates the location of the malfunction.

To verify a repair, clear info with the scan tool and run the EGR flow test keeping the following items in mind:

The PCM will only run the EGR flow test during a gradual deceleration.

The PCM will only run the EGR test during a closed throttle condition.

The PCM will only run the EGR test at vehicle speeds above 45 km/h (28 mph).

Several deceleration cycles, typically 9–12, will be necessary to run a sufficient number of EGR flow test samples.

The EGR Test Counter displayed on the scan tool can be useful in determining that the EGR flow test is running and to keep track of the number of test samples taken. The counter will increment each time a test sample is taken.

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Customer reply replied 8 months ago
Ok. Im not sure how to run a self test but I will figure it out.
What will it mean if the pintle moves during the self test? What if it doesn't?
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 8 months ago

Good morning.

If the pintial does not move during the self-test, that means the new EGR is faulty or it is not getting a signal from the computer. The wiring to the EGR valve could be an issue or the computer itself may be faulty. I know you said you checked the wiring, but let's be sure not to overlook anything.

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Customer reply replied 8 months ago
Ok.
Does your manual show you which pin in the computer provides the EGR signal. I think its a good idea to test it at the computer with the harness disconnected. Also is the computer in question the ECM or the PCM? Is it the one located behind the air cleaner?
Thank you
Customer reply replied 8 months ago
I removed the egr and with the scanner commanded it to open first 10 then 20, all the way up to 80 percent. The pintle opened up to accordingly. Since it is not my scanner and i am unfamiliar with it i was not able to run a self test. I could not find the command to run a self test.
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 8 months ago

Hello!

So your saying that the EGR functioned properly when doing this test?

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Customer reply replied 8 months ago
When i removed the egr valve i used the scanner to open it in 10% increments ip to 80%. Yes, the pintle appearrd to be functioning properly.
So what does that mean?
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 8 months ago

That means it is working. :)

So if you're still getting this code, I would check the MAP sensor, oxygen sensor and possibly go after the main engine computer.

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Customer reply replied 8 months ago
I understand how the map sensor and computer are related and plan on trouble shooting them next. Please Explain why i would get this code if my O2 sensor is bad. Wouldn't I get a bad O2 Sensor code if that were the case? Are you suggesting I replace the upstream sensor or the down stream sensor, or both?
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 8 months ago

I am not an engineer. I did not design this vehicle. But the computer must be able to verify that the EGR valve opened up when commanded. I don't know what sensor the computer uses to verify that the EGR valve actually opened up when commanded. However, I would think it would be one off these sensors. So I would recommend to check all of them to ensure a thorough job or diagnoses.

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Customer reply replied 8 months ago
Ok, i will be in touch.
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 8 months ago

Sounds good

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Customer reply replied 8 months ago
Please advise:
Day before yesterday we verified the egr valve was not giving a signal, neither actual or desired. Then yesterday we verified the egr works fine based on removing it and commanding it to open in 10% increments.
Today I retested the 5 wires going into the egr valve and wire A which is valve control coming from the computer is 0.03 volts with the car off and key in the on position I know the voltage fluctuates based on the operating conditions of the engine. However based on our discovery on Monday, that the actual and desired position of the egr valve were 0, is it reasonable to assume the computer is not sending the signal to the egr valve to open.
I tested continuity between the valve and the computer and it checks out.
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 8 months ago

Based on the information or test results, the EGR valve is working but the computer is not seeing it open like it should. So, provided the wires from the EGR valve are good, the only thing left would be a faulty computer, my friend.

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Customer reply replied 8 months ago
What about the 02 sensors you were speaking of?
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 8 months ago
What about it? You can certainly check it. :)
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Customer reply replied 8 months ago
I ordered the computer it should arrive in about a week. If the code clears up once I install it I will rate you appropriately so that you can get paid.
Thank you, ***** ***** be in touch.
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 8 months ago

Sounds good your welcome sir!

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Customer reply replied 8 months ago
HiCustomer
I installed the new computer today and now the car will not start. I reinstalled the old computer and the car starts just fine. With the new computer the starter does not even engage as if the battery were completely dead. Have you encountered this issue before? How do I resolve this? The computer was flashed when I purchased it.
Mel
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 8 months ago

Hi Mel!

Based on my experience, the security relearn needs to be done before the engine can start.

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Customer reply replied 8 months ago
Can you explain the process to me?
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 8 months ago

Turn ON the ignition, with the engine OFF.

Attempt to start the engine, then release the key to ON, the vehicle will not start. Observe the SECURITY light. After approximately 10 minutes, the security light will turn OFF. The vehicle is now ready to relearn the Pass lock Sensor Data Code and/or password ***** the next ignition switch transition from OFF to CRANK. Turn OFF the ignition, and wait 5 seconds. Start the engine, the vehicle has now learned the voltage reading coming back from the ignition switch.

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Customer reply replied 8 months ago
I installed the new computer. Took all day yesterday to get the car to 'relearn' what it needed. Took the car for a test drive just now and got code po401 about 5 miles down the road.
What now?
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 8 months ago

Go back and retrace your steps as you must have overlooked something.

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Customer reply replied 8 months ago
Could the purge solenoid valve be related.
When i put power to it as in turn the key should i feel it click or open?
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 8 months ago

I have not seen a purge valve cause this problem.. although I suppose it could be possible..

YES it should click as it opens and closes

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Customer reply replied 8 months ago
It was not clicking so I replaced the purge solenoid valve.
I loosened the exhaust pipe behind the catalytic converter but before the two mufflers and took it for a test drive. This time it still set the code po401 however it took much longer to set, I drove at least 10 miles further ranging from 20 to 55 mph most the trip. I still believe I have a plugged muffler.
Any ideas on how to test it?
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 8 months ago
sir. Check exhaust back pressure using a back pressure gauge.
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Customer reply replied 8 months ago
Purchased gauge. Will take a week to arrive.
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 8 months ago

OK

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Customer reply replied 7 months ago
I purchased a back pressure gauge and tested at the upstream 02 sensor port. I dont recall the exact numbers but according the the local smog tech my numbers are within tolerance and my muffler and catalytic converter are not plugged.
He scanned it with his equipment and says I have a 'flow' problem. He removed the egr valve and commanded it to open up to 80% while I had the vaccuum side of the EGR port plugged. He adjusted the rpms to be comparable to normal At 80% open then told me to unplug the intake/vaccuum sideof the EGR port. He expected the engine to suck in very hard and die. It did not die although it was sucking in through the intake port.
Any ideas?
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 7 months ago

Hello!

I am a bit confused.

So which port did not allow air to come through? The intake side?

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Customer reply replied 7 months ago
Both sides allowed air through fine. But he said that at 2500 rpms when unplugged the intake side it should die however it kept running.
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 7 months ago

The engine would only die if it were at idle when the intake side was unplugged. This is because engine vacuum is at its highest point at idle. So if there is a vacuum leak, it will only affect the engine at idle or with the throttle closed.

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Customer reply replied 7 months ago
Ok. I will keep trouble shooting
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 7 months ago

Sounds good

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Customer reply replied 7 months ago
Customer
Today I removed the exhaust manifold between the engine and the firewall in order to visually inspect for blockage or damage.
I found a very small exhaust leak where the crossover pipe bolts to the exhaust manifold at the front of the engine.
Could this exhaust leak be causing this trouble code?
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 7 months ago

YES sir it could.

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Customer reply replied 7 months ago
Ok, thank you.
I will puck up some gaskets and hopefully will have the engine reassembled soon. As soon as I take it gor a test drive I will uodate you?
Thanks again
Chevy Mechanic: AMEDEE, CHEVY TECHNICIAN replied 7 months ago

Yes sir, sounds good!

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