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Mike S.
Mike S., Chevy Mechanic
Category: Chevy
Satisfied Customers: 7368
Experience:  ASE Certified Master Technician
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I have a 2001 Chevy Suburban K1500 5.3L. I have recently

Customer Question

I have a 2001 Chevy Suburban K1500 5.3L. I have recently replaced the Intake Manifold, MAP Sensor, MAF Sensor, TPS Sensor, Both Bank 1 O2 Sensors, Water Pump (weeping), Fan Clutch and now the computer. The vehicle was running rough and generating random codes, which was why all the sensors were changed. The vehicle, after changing the intake was pouring fuel out the exhaust and showing heavy white smoke. This improved by changing the O2 Sensors and also, replacing one fuel injector which failed the unplug test. I also changed spark plugs, fuel and air filters. I eventually tracked the issue down to the computer. The blue connector had 11 pins that were corroded and shorted. I cleaned the connector with electrical contact cleaner, as well as cleaned the computer side. I filled the connector with dielectric grease and reassembled it. Upon restarting, all rich symptoms and other issues seemed to disappear. I idled the vehicle for about 45 minutes, then went for a test drive. After driving about 8 miles, the engine shut off and would not restart. After clearing the codes, the engine would restart. I idled for a couple of minutes and pulled back on the road. The vehicle immediately died again and would not restart until clearing the codes. I found that this cycle would repeat and every 15 seconds. I got to where I could clear the codes going down the road to keep the vehicle running. I ordered a used computer that was flashed for my mileage and vin. It arrived tonight and I installed it. After performing the passlock reset, I started the vehicle, let it idle for several minutes, with the parking brake on, and everything seemed fine. I took it out for a test drive and within a minute it started the whole dying cycle again. There are only two codes that are currently showing up, and they have been persistent throughout the whole ordeal, they are P0452 Fuel Tank Pressure Sensor Circuit Low Input and P1635 5-Volt Reference 1 Circuit Malfunction. I'm about to pull my hair out with this vehicle.
Submitted: 1 year ago.
Category: Chevy
Expert:  Mike S. replied 1 year ago.

P1635

The powertrain control module (PCM) uses a common reference 1 circuit as a sensor feed. This circuit supplies 5 volts to the following sensors:

  • The manifold absolute pressure (MAP) sensor

  • The exhaust gas recirculation (EGR) valve

The PCM monitors the voltage on the 5-volt reference 1 circuit. This DTC sets if the voltage is out of range.

This diagnostic trouble code (DTC) sets if the 5–volt reference circuit is shorted to ground.

Check that circuit for a short to ground. Here is the troubleshooting procedure,

Expert:  Mike S. replied 1 year ago.

That signal also goes to the fuel tank pressure (FTP) sensor, so it may be related and the same short to ground.

Expert:  Mike S. replied 1 year ago.

Here is that troubleshooting procedure, but it could turn out that if you fix the P1635 from finding that sensor feed circuit short to ground, you may have also fixed this P0452 codes as well, but the first circuit I would check is to the fuel tank pressure (FTP) sensor.

Customer: replied 1 year ago.
Would these be causing the engine shut downs?
Expert:  Mike S. replied 1 year ago.

Of course, you could be loosing the voltage to the map sensor and/or the throttle position (TP) sensor.

Customer: replied 1 year ago.
Live data shows the MAP and TPS to be reading correctly.
Expert:  Mike S. replied 1 year ago.

Ok, what about the rest of them? Are you going to at least read that procedure?

Customer: replied 1 year ago.
I did read it. I think I will have to just check the wiring by hand. My code reader only monitors 26 sensors and the fuel tank pressure sensor is not one I can monitor. I will get under it tomorrow and see what I can find out.
Expert:  Mike S. replied 1 year ago.

Didn't you say the problem was intermittent? Can you watch the map and tps while you are driving or running the engine when it stalls and see what the can tool tells you, if it's quick enough.

Customer: replied 1 year ago.
I wouldn't call it intermittent, the codes are immediate upon key on and return every time I clear them. The engine shut off seems to be consistant at every 15 seconds, unless the parking brake is set or you have your foot on the brake. The brake seems to postpone it. It occurs at idle or in gear.
Expert:  Mike S. replied 1 year ago.

Odd about it continuing to run with the brake on, I will look to see if there are any tsbs covering this but I am not promising anything. In the meantime, can you watch the map and tps readings while the engine stalls and let me know if you notice anything.

Expert:  Mike S. replied 1 year ago.

The only thing I could find on engine stalling is, engine starts then stalls and the Security lamp is flashing.

Is the security light on or flashing?

Customer: replied 1 year ago.
No, Security lamp is not illuminated. Security relearn procedure was successful. I had trouble with corrosion and shorting on the blue connector to the ECM, this is why I replaced the ECM. After I cleaned the connector is when it started the engine shutdown. Before that, it would just give erratic sensor readings and run very rich. Cleaning the connector fixed the erratic issues and the rich running, but seemed to give me another problem, that's why I assumed the ECM was fried. I'm going to go back and look at the red connector again and try to clean it again. I found that the Fuel Tank Pressure Sensor is pin 64 on the red side. The blue side had obvious problems, I didn't notice anything with the red side, but can't remember if I actually pulled the red cover off of the pins...
Expert:  Mike S. replied 1 year ago.

When the engine stalls, after coming to a stop, if you turn the key back to just run, will the fuel pump run again for 2 seconds?

Customer: replied 1 year ago.
I keep coming back to the ECM connector, even though I've cleaned it. I finally found a good pin out (didn't realize last night I only had half). The pins I had trouble with are the ones I'm still having trouble with. If I'm not getting a good contact on the reference pins, could it read low (short to ground)? I'm uploading a picture from before I cleaned it. This will be the blue connector with 1 & 41 to the left.
Customer: replied 1 year ago.
I have just noticed, using a custom view, on live data, that the MAP sensor stays at 3.5 inHG whether KOEOff or engine running. This leads me back to pin 43 ( I think it was) as it is a new sensor.
Expert:  Mike S. replied 1 year ago.

Replace that plug or the harness or whatever it is connected to. I can see it's shorting out.

Customer: replied 1 year ago.
The picture was prior to cleaning it. I just cleaned it again, but it may not be getting a good connection. Pin 2, 12 volt reference is pretty ate up.I also just unplugged the map sensor, the reading dropped to 3.0 and not 0.0, so I think there may be an issue in the wiring there.
Expert:  Mike S. replied 1 year ago.

I believe sensors are supposed to be receiving 5 volts. Let me double-check that.

Expert:  Mike S. replied 1 year ago.

Yeah, "The MAP sensor has a 5 volt reference circuit, a low reference circuit, and a signal circuit. The powertrain control module (PCM) supplies 5 volts to the MAP sensor on the 5 volt reference circuit. The PCM, also, provides a ground on the low reference circuit."

Expert:  Mike S. replied 1 year ago.

That code P1635 refers to Key on, and the PCM detected the 5v VREF 1 circuit was out of tolerance for 2 seconds. The EGR Pintle, Fuel Level, Fuel Tank Pressure, MAP and TP sensors all connect to this circuit.

So, if your map sensor is only receiving 3 volts, it is most likely on that circuit or pin, also.

Expert:  Mike S. replied 1 year ago.

I see at the pcm, the map signal wire is light green, pin 32/ connector 2.

The 5 volt is at pin 47/ connector 1, a gray wire.

Customer: replied 1 year ago.
I changed out the blue ECM connector today that had shorted. There is no change. I can't hear the fuel pump hum at anytime, but I did check fuel pressure last week when it was running so rich and it was running 45-50 lbs. no fuel in the vacuum line of the regulator. I put a dmm across all 3 contacts on the MAP sensor plug. I had 0 volts DC at the plug. I will be out of town most of the weekend, but I'm going to try and drop the tank soon and check the fuel tank pressure sensor.
Expert:  Mike S. replied 1 year ago.

Is the blue connector the #1 or 2 connector? They should be marked.

Do you have 5 volts at pin 47/ connector 1, a gray wire at the pcm?

The fuel pressure should be 55-62 psi, so you are a bit low.

Customer: replied 1 year ago.
I changed out the fuel pump and pressure sensor tonight. No more code for the sensor. Fuel pressure is no 55 key on and 50 running. It bumps to 55 when you goose the throttle, so the regulator is working. Tomorrow afternoon I'll try to track down the 5 volt problem. Now that I've eliminate one code, hopefully it will be easier to find the problem.Connector #1 is the blue, #2 is red. Is it the ECM side or the connector side to check with the dmm for voltage?
Expert:  Mike S. replied 1 year ago.

Leave it connected at first and back probe it.

Customer: replied 1 year ago.
Ok, finally got voltages... Connector #1: pin 45 FTP 5v, pin 46 TPS 5v, pin 47 MAP 2.27v, pin 48 EGR 2.29vI also have the same issues with two ECMs.
Expert:  Mike S. replied 1 year ago.

Each of those should have 5 volts.

See them pins here.

Expert:  Mike S. replied 1 year ago.

Do you have the same voltages on those 4 pins with the other ecm?

Customer: replied 1 year ago.
Pulled pin 47 out and replaced it with a dummy wire, back to 5 volts. Now to start back tracing the wire.
Expert:  Mike S. replied 1 year ago.

Sounds good.

Customer: replied 1 year ago.
I replaced the wire from the ECM to within 3 inches of the MAP sensor, retested the voltage and it's back to 2.2.
Expert:  Mike S. replied 1 year ago.

Replace the entire wire. Secondly, I thought the 5 volts was coming from the ECM to the MAP, is that where you said you got the 2.27 v, at the pcm pin or at the Map?

Customer: replied 1 year ago.
Voltage is at the pcm.
Expert:  Mike S. replied 1 year ago.

What was that voltage with the other ecm installed?

Customer: replied 1 year ago.
Same. 2.2v
Customer: replied 1 year ago.
Can you tell from your diagram which pin is the sensor ground for the MAP? I didn't replace the last 3 inches of the wire because I don't have a new plug for the MAP sensor end. I may be able to get by the junk yard tomorrow and get one. This is really messing with me, I can't see both ECMs being bad.