Crank-Start-Die After PCM Replacement


g1smith
08-23-2005, 10:26 AM
I just installed a used PCM for my '99 JGC Ltd.. The PCM is off from a '99 JGC Laredo. Both PCM's have the exact same part number and service update.

I am replacing it in at attempt to save my marriage, the wife is feed up with the intermittant stalls and the 5 - 30 minute wait for it to cool down.

After installing the replacement PCM, I'm now getting a crank-start-die condition, it starts and only runs for about two seconds then shuts off.
And of course, no error codes, no check engine lite. The door-open indicator lites up after it dies. The security system blinks fast for 10 or so seconds then starts blinking slow, so I believe that it is working.

I've read from other posts that after replacing the PCM with a used one, the only thing that would have to reprogramed would be the VIN, but that won't keep it from running.

Also, the only thing to watch out for with a used PCM is if your Jeep does not have the factory security system, then you can't use one from a car that has it. It learns to look for it and if you don't have it you can't disarm it. Both my 99 JGC Ltd and the 99 JGC Laredo have security devices!

Service Bullitins

081499 - VEHICLE START AND STALL OR VEHICLE NO-START Date: 05/21/99

Model year(s): 1999-2000

Description: Conditions with vehicle start and stall or vehicle no-start may exist from the interaction between a SKIS key and a Mobil Speedpass®. This condition occurs during cranking, when the Mobil Speedpass cylinder is held immediately adjacent to the key being used to start the vehicle.


181399 - EXHIBITING AN ENGINE NO-START CONDITION Date: 06/18/99

Model year(s): 1999

Details: THIS INFORMATION APPLIES TO VEHICLES BUILT BEFORE APRIL 27, 1999 AND NOT EQUIPPED WITH THE SENTRY KEY

IMMOBILIZER (SKIM) SYSTEM. An engine no-start or an engine crank-start-die condition may exist with vehicles not equipped with SKIM. Diagnostic Trouble Codes P1685 "SKIM Invalid Key" and/or P1686 "No SKIM BUS Messages Received" may be present in the PCM.

This condition may be due to erroneously learning of SKIM by the PCM. In most cases, the vehicle will start once the vehicle battery has been disconnected to reset the PCM.

SteveB05
08-23-2005, 07:45 PM
Are you able to keep it running with some throttle? The PCM needs to learn where idle is and may take some time to do so.

g1smith
08-24-2005, 01:28 PM
Nope, can't keep it running with lots and lots of throttle.

My Generic OBDII Scanner reads nothing, but, I did the "key dance", on-off-on-off-on) to retrieve the trouble codes and the odometer displays P1685!

P1685 SKIM - Smart Key Immobilizer Module
The engine controller has received an invalid key from the SKIM.

One OBDII Diagnostic site indicated that P1685- SKIM Invalid Key refers to - Driver 5 Line 5 . . . so if one wanted to by-pass the SKIM and compromise your vehicles security by jumping some wires, or removing the SKIM . . . naaa! I like the Jeep if it would just keep running!

Other posts indicate that the key loop may not be reading my key correctly because my keys SKIM code doesn't match what is programed into the PCM computer.

Can you say Dealer? I might as well get my VIN programed into the computer along with the SKIM key and remote codes.

One poster on http://www.automotiveforums.com/t412556.html
states that after they replaced the ECU on their 2001 ATX SOHC, it won't start. But when they disconect the SKIM module, the P1685 code dissapears.

dksob81
08-24-2005, 01:46 PM
you need to take it to the dealership so they can reprogram the key, Sentry key system.

g1smith
08-30-2005, 02:06 PM
I'm ready to declare success. The past 6 weeks of intermittant stalls followed by 5 - 30 minute waits on the side of the road for the PCM to cool down seems to have been cured by a used PCM replacement. Result, marriage saved. I think that is a good thing? Are the PCM's a common failure item in the 99 JGC Ltd 4.7 V-8 or was I just one of the unlucky few?

Add your comment to this topic!