P1635 dtc

[spanks]

Hey guys. Got an issue with a 1999 Holden Commodore Gen3. Bringing up DTC P1635 5V reference circuit 1 which effects MAP,TPS and oil pressure switch. Voltage is varying between 1.9 and 3 volts at the sensors. Output from the sensors is around 0.02-0.04 at idle dependant on the sensor. Have had the PCM checked (no fault found) have also replaced PCM with a known good one just to be sure. Have checked engine earths,PCM grounds at terminal plugs. All good. Checked continuity in loom between sensors and PCM. Sort of at ends to try to work this out and need help. Not a lot of info on the code available. odes P0107 MAP signal low and P0522 Oil pressure signal low are also present. Understandably as the input is low. Thanks in advance if anyone can help. Cheers

[compsystems66]

If you unplug all of the sensors that use the 5v reference, what voltage do you have coming from the PCM?

If you have 5v with all sensors disconnected, start plugging them in one at a time until the voltage drops low. You may have a sensor that has an internal short.
If you still only have 2-3 volts with all sensors disconnected I would suspect a pinched wire, or bad connection on the harness somewhere, or bad PCM.

Where exactly are you reading the 5v voltage from? The end of a sensor connector like the MAP plug, or right off the PCM wire?

[spanks]

I have 1.9-3 volts at all sensors when they are all disconnected. Have had the PCM checked and no fault found. I have then tried another known good PCM just to make sure. Have done continuity tests on the loom and all wiring seems good. Have checked the PCM grounds looking for earth leaks. Have checked all other earths going to engine. They are all good also. Checked for voltage at the sensor plugs.