I have been troubleshooting Camshaft Position Sensor no-start issue in this thread for my 2007 Chevrolet Aveo. Long story short - in one of the answers it was suspected that camshaft position sensor is not getting stable 12V, so as a test it was suggested to connect Battery+ directly to the sensor's camshaft position sensor's Orange pin and car started successfully. Now, it surprisingly also starts without connecting the Orange pin directly to the Battery+ anymore.
However, I want to root cause this issue properly so that it does not happen again while I am driving.
Today I did a test where I measured voltage on Sensor Harness'es Orange wire with and without "main relay" plugged in when key was in "ON", position:
As can be seen the voltage without relay is 2.4V, which I think is wrong. It should have been 0V. My questions are:
- Based on this test, can I conclude that "main relay" most likely is actually OK?
- Since I see 2.4V without main relay, then does it mean that there are two power wires with different voltages shorted together after the main relay?
- If so, then can that information of knowing 2.4V can be used to pinpoint the other wire that is shorted with the Orange wire?
- The obvious way to me seems to open all the splices in the fusebox after "main relay" power wire and see from which wire the 2.4V are coming and then just keep going forward until wire with 2.4V is isolated. Of course I would need to restore splices to the original condition after that. Any other better tips on how should I approach this problem?
P.S. May or may not be related - I have red Airbag light on for more than a year. Chevrolet dealership did not know how to root cause, because there "were no SRS codes". Could it be that AirBag is using 2.4V and has shorted somewhere with Camshaft position sensor power wire hence both issues? Though the timing does not match when both issues started to manifest themselves.
Update#1: I added load (resistor and yellow LED light) between sensor harness'es orange wire and Battery -. Voltage dropped from 2.4V to 1.98V, and the LED did light up (the alligator wire from battery- to the breadboard changes color to white and is not captured in the picture):
Update#2: Voltage measurements when key was in "ON" position ("Voltage between Battery Minus and" column should be correct. However, in "Voltage between Orange and" I may need to redo some measurement, because I think somewhere there I should see 0.4V and 10.1V):
If my interpretation is correct, then here is how last test with both fuses and relay removed looked like. Since there was continuity only between EMS1(R) and EMS2(L) then I assumed that those pins must be the ones facing Main relay.
I guess what this test suggests is that EMS1(L) and EMS2(R) and something else with voltage >2.4V is shorted together? Also, there was 109KOhm resistance between EMS1(L) and EMS2(R).
With the battery disconnected the 107KOhm resistance between EMS1 and EMS2 changed to infinity once I unplugged the upper cable to PCM as well:
Also, with key in ON position and Main relay, EMS1 fuse and EMS2 fuse unplugged I got following voltage measurement between Battery Minus and CMP Orange wire:
- Upper cable and lower cable to PCM plugged in - 2.4V
- Upper cable to PCM plugged and lower unplugged - 11.81V
- Upper cable and lower cable to PCM unplugged - 0V.
So my latest 2 questions are:
Does this mean that PCM is malfunctioning and it is the reason why I see those 2.4V on CMP Orange wire even with EMS2 fuse removed? Or there is still possibility of something else causing that 2.4V on Orange sensor wire (e.g. after unplugging PCM the hypothetical 3rd circuit was not getting power hence it could not cause voltage leak on EMS2 circuit)?
Why with lower cable to PCM unplugged, but upper one plugged, I suddenly start to see 11.81V instead of 2.4V or 0V?
Update#4: With the key in "OFF" position and both PCM cables unplugged I connected Battery Plus directly to EMS1 terminal (that is facing harness, not main relay) and then measured voltage between Battery Minus and EMS2 fuse terminal that is also facing harness. As can be seen the voltage is 0V which I believe proves that there is no direct leak between EMS1 circuit and EMS2 circuit.
- In the past I incorrectly called CMP's "Orange" wire as "Pink" wire. It is actually Orange for my notchback model and presumably Pink for hetchback model.