I also found this posted online... can anyone confirm what he says??
"Hi maybe I can help.Im a chrysler/jeep technician. Ive seen these problems many times. Although I cant pinpoint your fault without seeing it ,here are some things that I have run into..
First know this. Any sensor cam/crank/tps etcc..) that has a reference voltage from the pcm can cause this issue.
these sensors,(ESPECIALLY THE CRANK SENSORS) CAN SHORT OUT INTERNALLY. THIS WILL CAUSE A NO START CONDITION AND A "NO COMMUNICATION" ISSUE WITH THE PCM. This condition has caused numerous unneeded pcm replacements. It gets difficult to diag when its an intermittent problem. sometimes a tech will install the pcm and let the jeep leave. Then when temp is right, the sensor shorts and it all happens again. Often by the time the jeep shows up on the hook the engine has cooled and the short is gone. In this case the tech has nothing to go on. YOU MOST LIKELY WONT HAVE A CODE HERE.
THIS IS HOW I DIAGNOSE THE ISSUE. WHEN THE CONDITION IS PRESENT(NO COMMUNICATION") wITH THE KEY ON, START DISCONNECTING EACH SENSOR THAT HAS A REFERENCE VOLTAGE. START WITH THE CRANK SENSOR. IF YOU SEE THE SCANNER GET COMMUNICATION, THEN YOU FOUND THE SHORTED SENSOR.tHIS CAN BE A PAIN IN THE ASS IF THE CONDITION IS INTERMITTENT.
PLEASE NOTE: IT IS EXTREMELY RARE THAT THE PCM ITSELF HAS CAUSED THIS CONDITION. 99% OF THE TIME ITS A SENSOR SHORTING OUT, WIPING OUT ALL COMMUNICATION.
ALSO NOTE: i HAVE NEVER SEEN THIS CONDITION ACTUALLY DAMAGE THE PCM. ONCE THE SHORTED SENSOR IS REPLACED, THE PCM IS FINE. THERE IS A RESISTOR IN THE PCM THAT PROTECTS IT FROM THIS.
sOMEONE IN THE FORUM WROTE THAT THE DEALER SAID THAT THE SENSOR SHORTED AND DAMAGED THE PCM. THEY SAID THE GOT A NEW CKP,CMP AND PCM. THATS THE STORY THAT IS USED WHEN THEY REPLACED THE PCM FIRST FOR NOTHING, WHEN IT WAS A SHORTED SENSOR THAT WAS THE PROBLEM ALL ALONG.
IVE SEEN THAT HAPPEN TOO.
I NORMALLY WOULDNT GIVE OUT MY OWN PROCEDURES BUT YOU ALL SEEM FRUSTRATED.
I DONT KNOW WHAT CLIMATE YOU LIVE IN BUT IT MAKES A DIFFERENCE. I LIVE IN TORONTO. WE HAVE HOT SUMMERS AND COLD WINTERS, MAYBE THATS WHY IVE SEEN THIS SO MANY TIMES.
GOOD LUCK, LET ME KNOW IF I HELPED YOU OR MADE THINGS MORE CONFUSING.
THANKS j. "