My jeep stalled and will not start again. It just keeps cranking over.
Gauges are not functional aside from dummy lights & odometer (always been an intermittent problem that could be fixed by shutting off the jeep and starting it again)
Communication Error through OBDII port
Diagnosing the no spark issue, I found there to be no power to the connector for the Crank Position Sensor. The connector to the distributor has 2.5v with the ignition ON, and drops to 2.1v when I try cranking it over.
All under-hood fuses are good.
This leads me to believe the issue is either with the wiring between the battery and the CPS connector, or within the ECM. Judging by the other issues, I'm putting my money on ECM.
Does it seem likely that the ECM would just die all of a sudden?
The "Mall Crawler" - 1998 ZJ Grand Cherokee 5.2 V8, 5.5" LongArms, 32s, 12000lb winch & more.
the crank sensor or o2 sensor can short out and cause problems with the reference and supply circuits inside the PCM. Many times the PCM is disabled by the shorted sensor causing loss of com and no CEL for 3 seconds when the switch is in the ON position.
So if you remove these from the equation and the PCM comes back to life, there you go.
Like I said all the under hood fuses are good. Is there an ECM fuse somewhere else?
What ZeeJay was describing does not go through your fuses. The ECM has a small power supply in it that creates a 5V reference from the 12V battery voltage, and this reference powers all your sensors. If it is shorting, then it could cause the PCM to completely shut down.
But, this is not where I first probe to see if my PCM were dead. The test points I would go though are shown in the diagram below.
(1) I would be first interested to see if the PCM starts to go through some of its initiation, and in particular I would be interested to see if the PCM is activating the ASD relay when it first starts up. It should for about 2 seconds. To test, you can disconnect any of your fuel injectors and place your meter between the Dark Green / Orange wire of a fuel injector connection and a ground point. When the key is turned to the "on" position, you should see 12V present for about 2 seconds.
(5) If the PCM is staying on, then 5V should be at the TPS or the Camshaft Position Sensor (on your distributor). If not, then I would test points (2) and (3) to see if I have voltage going to my PCM.
(2) I would check the voltage on both sides of fuse 20 (powers PCM)
(3) Then, I would disconnect my PCM connector #1 to see if I have voltage on pin 22.