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code p1668 help

35K views 5 replies 3 participants last post by  smokin dually 
#1 ·
I am working on a 96 that is throwing the p1668 code it says pcm-idm communication. I have tested the pcm and the idm on different trucks and they are fine. What other components can I check?
 
#2 ·
DTC P1668 and P1670 indicates that a communication error has occurred between the PCM and the IDM.
Possible causes:
Open fuse
IDM relay
Open or shorted IDM enable circuit
Open/short in EF circuit
Open/short in FDCS circuit
IDM powering circuits
PCM
Check for other codes
 
#3 ·
no other codes. I changed around the relays and the truck srarted, but now it has a short in it. The wait to start light flashes constantly and the lights in the dash flash. It's almost like you are turning the key on and off really fast.
 
#4 ·
Just for drill disconnect the fuel heater. They like to fail and short on out the PCM circuit but I have not read of anyone having this exact set of problems. I would also be checking out those relays.

Tom
 
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