Every key start this sets P1635 5 volt reference 1 code

Fred Owner/Technician California Posted   Latest   Edited  
Resolved
Driveability
2002 Chevrolet Venture LT 3.4L (E LA1) 4-spd (4T65-E) — 1GNDX03E92D228554
P1635

Starts everytime runs a little rough for 3 to 5 seconds most of the time, like its loading up. Code will not set unless the engine is running, I can cycle the key on and off over and over the code will not set. I tested all powers and grounds at the computer the grounds were .08 volts, I cleaned them, now its .02 volts still same code comes up, I completely disconnected the Alternator same code. The coolant has .31 volts in it, can this be cause for the code, the spec I find is .05 volts.

Labscope connected to all 4 of the 5 volt references at the computer I see no drops or spikes.

What next?

Thanks 

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Todd Diagnostician
Michigan
Todd
 

I assume the scope was grounded to the engine or battery? If it was, I would ground the scope at each of the low reference points going back to the PCM and 5 volt references. Based on what you've found so far I suspect that the low reference will be open circuit in the PCM (even if only temporarily).

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Albin Diagnostician
Washington
Albin
 

The code set criteria for that DTC is: Conditions for Running the DTC is: The engine is running. Conditions for Setting the DTC - The PCM detects a voltage out of tolerance condition on the 5-volt reference A circuit. - The above condition is present for longer than 10 seconds. Knowing that, should make the testing for the problem rather easy. Since you have a scope hooked up, scope the…

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Geoff Diagnostician
Hawaii
Geoff
   

Verify the “Low Reference” circuits at the PCM are indeed at ground. Watch the 5V REF in the data list, if you can. (I think it was there in 2002). Gently flex the PCM connectors while watching the 5V value.

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Sam Mobile Technician
Michigan
Sam
 

I have seen several of these. Measure your 5 volts at the TPS while running. Do not be surprised if it is over 6 volts. The fuel tank pressure sensor, egr and ac pressure are all on the 5 volt reference line. It is all the same inside the pcm. Unplug things until your reference voltage drops to 5. or raises to 5. I have found the most likely culprit is the EGR or the connector under the body…

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Helpful
Fred Owner/Technician
California
Fred
 

Update Scope is connected to battery ground Return voltage from TPS, MAP, EGR, FUEL TANK PRESSURE SENSOR solid 5 volts is 5.03 KOEO 5.1 volts KOER max most times its 5.08 volts It must be an internal PCM problem

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Eric Owner/Technician
Wisconsin
Eric
 

Fred, Nope, doesn't have to be. Did you miss where it was suggested that you check the low reference or signal return wire, in other words, the grounds (more than one) for the 5 volt sensors in the PCM, at the PCM connector? Eric

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Fred Owner/Technician
California
Fred
   

Thanks, I did check all Powers, all 5 volt references, all Low references, and all Grounds directly at the PCM, nothing stood out, all signal returns from TPS, MAP, EGR, FTP sensor every sensor that is on a 5 volt circuit was tested even though this code is connected to the 5volt ref A circuit I did test the 5 volt ref B

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Eric Owner/Technician
Wisconsin
Eric
 

Fred, When chasing any problem with a reference voltage from a control module it is important to verify the system by connecting the scope ground cable to the module low reference (reference voltage ground circuit) at the PCM connector. Connecting the scope or dvom ground at the battery ground while testing the reference voltage from the control module will not give you reliable results…

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Disagree
Fred Owner/Technician
California
Fred
 

We replaced the PCM no more code, after testing all 5 volt references, grounds, powers, low reference voltages using ATS escope Elite 4 we see nothing that could cause this code P1635 New PCM was the fix Thanks for your help PS. I Don't see how to close this with a resolution

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Sam Mobile Technician
Michigan
Sam
 

I always edit the original message and place an update of the repair. SO if someone searches this later they don't have to go through the comments to find the fix.

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Fred Owner/Technician
California
Fred Resolution
 

Replaced the PCM problem solved

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Resolution Ð Awarded