Testing 5v from PCM?
#12
11-20-2020, 07:26 PM
Doing Live Scan with the Blue Driver- while cranking- showed
Did not see tach bounce this time on the gauge (I could swear I saw it bounce yesterday), and no rpm's shown on scanner
Engine coolant temp showed lower limit, -40 degrees
Intake air temp same- lower limit, -40 degrees
Fuel system- "unknown".
Recap:
Voltage present from ASD to coil (checked w/volmeter). As I understand it, the PCM would need a signal from the crank sensor to activate the ASD (also, swapped the ASD relay with A/C clutch which I knew was fine). If so, the crank sensor would be functioning (and, no code present for faulty crank sensor). No switching signal to coil, checked with test light on the switching wire while cranking. Switching signal comes (or not in this case) from PCM.
Any reason to think this is the crank sensor, and not the PCM or something else (though, no clue what "something else" could be)?
Did not see tach bounce this time on the gauge (I could swear I saw it bounce yesterday), and no rpm's shown on scanner
Engine coolant temp showed lower limit, -40 degrees
Intake air temp same- lower limit, -40 degrees
Fuel system- "unknown".
Recap:
Voltage present from ASD to coil (checked w/volmeter). As I understand it, the PCM would need a signal from the crank sensor to activate the ASD (also, swapped the ASD relay with A/C clutch which I knew was fine). If so, the crank sensor would be functioning (and, no code present for faulty crank sensor). No switching signal to coil, checked with test light on the switching wire while cranking. Switching signal comes (or not in this case) from PCM.
Any reason to think this is the crank sensor, and not the PCM or something else (though, no clue what "something else" could be)?
The temperature lower limits are because of the codes you saw related to the sensors. Either there is some voltage bleeding onto the sensor wires or more likely (I asked about it above) the circuit is not closed (circuit high in OBD speak). The PCM sees very high resistance outside of the programmed values and sets the temps to the lower limit.
Sorry for asking obvious questions but I used to make my living testing and troubleshooting complex electronic equipment: The PCM side of the coil has power/test light on and never flickers during cranking ?
If you want to test the 5V sensor power (the original question) the easiest way is at the TPS or MAP, both have a violet/white wire that comes from the same PCM pin via a splice. That splice also connects to the crank position sensor and the cam position sensor so you might want to check power at those too in case the splice is no good anymore.
The only other thing I can think of is the cam position sensor itself being bad. Here's a good writeup how to test it: https://troubleshootmyvehicle.com/ch...e-cmp-sensor-1
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Lynn Wells (11-21-2020)