JEEP Grand Cherokee Check Engine light and PCM issues
I have 3 Grand Cherokees(1994, 2004 and 2008 diesel) which we dearly love but the 2004 with the 4.0L engine (110,000 miles on it) has the Check Engine light problem. We now believe it has been fixed. It would throw codes for O2 sensors which we repeatedly changed and the code would come back after a cojuple of hundred miles, transmission codes, TPS codes, A/C quit working, engine would stumble sometimes but never stall. finally the dealership said it was the PCM. So we changed that and the O2 sensor and Trans Sensor codes returned within 4 miles of travel.
Finally after 3 days in the shop they found that the PCM wiring plug that goes through the firewall had badly corroded terminals and the voltage was flucuating. We changed the wiring plug and it is now behaving perfectly ..... at least for now. Fuel economy is back where it should be too. I haven't tried the A/C yet to see if it is working
I negotiated a settlement with the dealership as I told them they should have checked the wiring harness before changing the computer and they agreed. This vehicle spent its first 4 years in Toronto, Ontario which is a heavily salted road system. I expect this connector is likely corroded on many Eastern and Northern vehicles where road salt is frequently used.