How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Chad Farhat Your Own Question
Chad Farhat
Chad Farhat, ASE Certified Technician A6 - Electrical / Electronic systems A7 Heating / Air conditioning systems
Category: Chevy
Satisfied Customers: 1573
Experience:  Owner at Carolina Auto Service & Sales , 20 years Experience in Foreign & Domestic vehicles A6 - Electrical / Electronic systems A7 Heating / Air Conditioning systems
45790705
Type Your Chevy Question Here...
Chad Farhat is online now
A new question is answered every 9 seconds

Chevy Cobalt VIN 1G1AK58F487127625 I am receiving a P0340.

Customer Question

Chevy CobaltVIN 1G1AK58F487127625I am receiving a P0340. When I do the live plot test it shows the cam reading dropping out then coming back. So I replaced the cam sensor. I also had a P0334 so I replaced the crank sensor as well. Only the P0340 comes back.
Submitted: 2 months ago.
Category: Chevy
Expert:  Chad Farhat replied 2 months ago.

Hi, I'm Chad. Welcome to JustAnswer. I'm reviewing your question and I will be posting your reply ASAP.

Expert:  Chad Farhat replied 2 months ago.

Hey how are you

Please read the following trouble shoot

if the sensor were replaced , wiring & ECM needs checking

this is the circuit diagram for the cmp & ckp , please check

https://www.dropbox.com/s/t9yyrgza1fwmpq1/3.gif?dl=0

DTC P0340 Diagnostic Instructions * Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. See: Vehicle > Initial Inspection and Diagnostic Overview * Review Strategy Based Diagnosis for an overview of the diagnostic approach. * Diagnostic Procedure Instructions provide an overview of each diagnostic category. DTC Descriptor DTC P0340 - Intake CMP Sensor Circuit Diagnostic Fault Information

Circuit/System Description The 4X camshaft position (CMP) sensor circuits consist of an engine control module (ECM) supplied 5-volt reference circuit, low reference circuit, and an output signal circuit. The CMP sensor is an internally magnetic biased digital output integrated circuit sensing device. The sensor detects magnetic flux changes of the teeth and slots of a 4-tooth reluctor wheel attached to the camshaft. As each reluctor wheel tooth rotates past the CMP sensor, the resulting change in the magnetic field is used by the sensor electronics to produce a digital output pulse. The sensor returns a digital ON/OFF DC voltage pulse of varying frequency, with 4 varying width output pulses per camshaft revolution that represent an image of the camshaft reluctor wheel. The frequency of the CMP sensor output depends on the velocity of the camshaft. The ECM decodes the narrow and wide tooth pattern to identify camshaft position. This information is then used to determine the optimum ignition and injection points of the engine. The ECM also uses CMP sensor output information to determine the camshaft relative position to the crankshaft, to control camshaft phasing, and for limp-home operation. Conditions for Running the DTC P0340 * The engine is running. * DTC P0340 runs continuously when the above condition is met. Conditions for Setting the DTC P0340 The ECM does not receive 4 camshaft pulses within 3 seconds. Action Taken When the DTC Sets DTC P0340 is a Type B DTC. Conditions for Clearing the MIL/DTC DTC P0340 is a Type B DTC. Circuit/System Verification 1. With the ignition OFF, inspect the engine wiring harnesses carrying the CMP sensor circuits for the following conditions: * Close routing of aftermarket electrical equipment * Close to solenoids, motors, and relays Correct any wire harness routing or component placement conditions, if it is determined to be a possible source of electrical interference. 2. With the ignition ON, engine OFF, use the live plot function on the scan tool. Select the engine speed parameter and the CMP sensor parameter. Change the minimum spec to 400 RPM for both parameters. Change the maximum spec to 4,000 RPM for both parameters. 3. Start the engine and observe the scan tool. 4. Quickly accelerate and release the accelerator pedal several times. Do not accelerate past 4,000 RPM. The 2 graphed lines on the live plot display should track together across the screen. 5. Operate the vehicle with the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data. Circuit/System Testing P0340 1. Ignition OFF, disconnect the appropriate CMP sensor wire harness connector. 2. Test for less than 1 ohm between the low reference circuit terminal B and ground. ^ If greater than the specified value, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM. 3. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal A and ground. ^ If less than the specified range, test the 5-volt reference circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the ECM. ^ If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM. 4. Ignition ON, test for 4.8-5.2 volts between the signal circuit terminal C and ground. ^ If less than the specified range, test the signal circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the ECM. ^ If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the ECM. 5. Ignition OFF, connect a fused jumper wire to the CMP signal circuit terminal C. 6. Ignition ON, momentarily touch the other end of the fused jumper wire to the battery negative post. The CMP active counter parameter on the scan tool should increment. ^ If the CMP active counter increments, replace the CMP sensor. ^ If the CMP active counter does not increment, replace the ECM. Component Testing Important: You must perform the Circuit/System Testing before proceeding with Component Testing. 1. Inspect the CMP sensor for correct installation. Remove the CMP sensor from the engine and inspect the sensor and the O-ring for damage. ^ If the sensor is loose, incorrectly installed, or damaged, repair or replace the CMP sensor. 2. Connect the CMP sensor connector to the CMP sensor. Turn ON the ignition, with the engine OFF. 3. Ignition ON, and engine OFF. Observe the CMP Active Counter parameter on the scan tool. Pass a steel object by the tip of the sensor repeatedly. The CMP Active Counter parameter should increment. ^ If the parameter does not increment, replace the CMP sensor. Repair Instructions Perform the Diagnostic Repair Verification after completing the diagnostic procedure. See: A L L Diagnostic Trouble Codes ( DTC ) > Verification Tests

© 2016 ALLDATA, LLC. All Rights Reserved. Terms of Use (Version 2.0.13801)

Please let me know if you need anything else on it, just reply back and we will continue

If you are good, Please Kindly Rate Me.

A 5 Star Rating is much Appreciated

If you feel I have not been helpful Please DO NOT RATE ME BAD OR POOR (1 or 2 stars) ,You can always ask me again or I can opt out of your question & open it for another expert ,that will provide you with more or better assistance on this issue

Please keep in mind that when you rate me , it does not end our conversation.

you can always come back to this conversation and ask me any follow up question you may have on this issue

(you can copy this link page & paste it in your browser when ready and it will open up our conversation again)

Thank You
Chad Farhat
ASE Certified Technician

Customer: replied 2 months ago.
What should be considered high resistance for this circuit?Test for less than 1 ohm between the low reference circuit terminal B and ground. ^ If greater than the specified value, test the low reference circuit for an open/high resistance.
Expert:  Chad Farhat replied 2 months ago.

anything greater than 1 ohms will be high, i think that is what you asking, ask me again if it is not

Customer: replied 2 months ago.
With the circuit unplugged from the ECM is anything over 1 ohm considered high resistance?
Expert:  Chad Farhat replied 2 months ago.

yes sir

Expert:  Chad Farhat replied 2 months ago.

wait 5 minutes after unplugging the ecm then take reading

Customer: replied 2 months ago.
Ok
Expert:  Chad Farhat replied 2 months ago.

sounds good

just let me know if you need anything else on it

Thanks

Chad

Customer: replied 2 months ago.
When I did the first resistance test, my resistance was 3.2 ohms. Once I disconnected the ECM (and waited 5minutes) my resistance was .9 ohms. Reconnected the ECM to recheck. Now my resistance is down to .9 ohms. Suggestions?
Expert:  Chad Farhat replied 2 months ago.

try to start it or cycle the switch & retest with ecm plugged in what is you resistance stayed 0.9 or went back up ?

Expert:  Chad Farhat replied 2 months ago.

have you done a wiggle test on the sensors harnesses or wires and watched if the signals comes on goes ?

Customer: replied 1 month ago.
This morning I went and drove it and rechecked the resistance after the test drive. It read 17.9 ohms. I unplugged the ECM connector and rechecked the wire. Wire had .9 ohms. Reconnected the connector and now the reading is 1.4 ohms. I'm suspecting the ECM.
Expert:  Chad Farhat replied 1 month ago.

yes , i agree get another ecm and try it

Look into rebuilding it instead of used, then you dont need scanner to program it after you get it

Please let me know

Thank You

Chad Farhat

ASE Certified Technician

Customer: replied 1 month ago.
I know how and have the equipment to program GM vehicles.
Expert:  Chad Farhat replied 1 month ago.

ok cool you have GM Tech II

Expert:  Chad Farhat replied 1 month ago.

Please keep in mind that when you rate me , it does not end our conversation.

you can always come back to this conversation and ask me any follow up question you may have on this issue

(you can copy this link page & paste it in your browser when ready and it will open up our conversation again)

Thank You
Chad Farhat
ASE Certfied Technician

Customer: replied 1 month ago.
I also have the MDI
Expert:  Chad Farhat replied 1 month ago.

I like tools been collecting for years

Related Chevy Questions