Dragon5126
New member
Before you submit to replacing the PCM (Powertrain Control Module) as the computer is properly called by Jeep/Chrysler, here is a quick tutorial on how to correct MOST problems that present as a defective unit. it requires a 30 watt (average) soldering pencil, some thin 60/40 ROSIN CORE solder (NEVER USE ACID CORE! it will destroy the unit!) and some Deoxit from Radio Shack. Deoxit is liquid magic! I have used it for decades in the electronics arena to stop erratic issues that were otherwise like chasing ghosts. It is fantastic for electrical/electronic connections in severe environments such as in an engine compartment. (No I dont own stock in the company, but wish I did!!!)
When you have your supplies together,remove the two screws in the cover and gently pry the tabs holding the covers on the PCM up. The small cover will come right off, the larger one will have to be gently pried off as it is actually the 5 volt regulator board of the PCM. This is the focus of our attention. turn it over and carefully clean any of the jelly potting compound from the solder pads of the connector strip that plugged into the other part of the unit. Now using as little solder as you can, carefully flow fresh solder onto each pad and the connector that is on the pad. It will take a bit of time to get it to flow due to the type of board material the unit is made out of so dont get impatient. when you ge a good solder joint move to the next pad inline, dont jump pads, the warming of the pard itself will speed things up. Be careful not to damage any of the components on the board or the copper traces that connect them.
When you have resoldered every pad, let the board cool, and treat the connector socket with the Deoxit... make sure yiu get it into the holes in the connector, and carefully treat the pins in the other half of the PCM where this connecter plugs into. Reassemble the unit, carefully bend the tabs back down into place. and replace the screws. WARNING! Some units have come frome the factory with screws that were too long, and eventually due to vibration shorted the unit out. I replace them with shorter sheet metal screws as standard operating procedure to avoid this issue, since I never ran into this personally.
Treat the external pins on the PCM with the Deoxit before reinstalling it in the Jeep. It is estimated that the repair I just outlined (except for the deoxit) will correct between 70-95% of all PCM problems. This is the same rebuild procedure that is done by the companies that sell the rebuilt units. As an experienced Electronics Engineer, I have gone the extra step and added the use of a deoxidizer on the connectors, which will protect the connections as well as increase their electrical integrity. I have personally used this cure myself on several Jeeps having been a longtime Jeeper with myfirst being a 76 Cherokee S. I currently have a 95 GC Limited, a 98 GC Laredo, and an 06 Wangler. You cant have just one!
As a side note on the deoxit...and this repair, my 98 GC was throwing O2 sensor errors with new sensors and irratic charging issues. I repaired the PCM as outlined and the O2 issues went away. I pulled the Alternator and took it to autozone (4 blocks from the house) and had it tested... it was fine... so I cleaned the contacts for the wiring harness and treated it with deoxit, and reinstalled... started Romero up (yes I name my Jeeps... Willie, Romero and TJ) the dash gauge indicated just under 14 volts and my DMM indicated a steady 13.81 volts and not a problem since... Like I said Deoxit is liquid magic. it should be in every tool kit if you deal with automotive electrical/electronics. It isnt cheap but it's worth it.
When you have your supplies together,remove the two screws in the cover and gently pry the tabs holding the covers on the PCM up. The small cover will come right off, the larger one will have to be gently pried off as it is actually the 5 volt regulator board of the PCM. This is the focus of our attention. turn it over and carefully clean any of the jelly potting compound from the solder pads of the connector strip that plugged into the other part of the unit. Now using as little solder as you can, carefully flow fresh solder onto each pad and the connector that is on the pad. It will take a bit of time to get it to flow due to the type of board material the unit is made out of so dont get impatient. when you ge a good solder joint move to the next pad inline, dont jump pads, the warming of the pard itself will speed things up. Be careful not to damage any of the components on the board or the copper traces that connect them.
When you have resoldered every pad, let the board cool, and treat the connector socket with the Deoxit... make sure yiu get it into the holes in the connector, and carefully treat the pins in the other half of the PCM where this connecter plugs into. Reassemble the unit, carefully bend the tabs back down into place. and replace the screws. WARNING! Some units have come frome the factory with screws that were too long, and eventually due to vibration shorted the unit out. I replace them with shorter sheet metal screws as standard operating procedure to avoid this issue, since I never ran into this personally.
Treat the external pins on the PCM with the Deoxit before reinstalling it in the Jeep. It is estimated that the repair I just outlined (except for the deoxit) will correct between 70-95% of all PCM problems. This is the same rebuild procedure that is done by the companies that sell the rebuilt units. As an experienced Electronics Engineer, I have gone the extra step and added the use of a deoxidizer on the connectors, which will protect the connections as well as increase their electrical integrity. I have personally used this cure myself on several Jeeps having been a longtime Jeeper with myfirst being a 76 Cherokee S. I currently have a 95 GC Limited, a 98 GC Laredo, and an 06 Wangler. You cant have just one!
As a side note on the deoxit...and this repair, my 98 GC was throwing O2 sensor errors with new sensors and irratic charging issues. I repaired the PCM as outlined and the O2 issues went away. I pulled the Alternator and took it to autozone (4 blocks from the house) and had it tested... it was fine... so I cleaned the contacts for the wiring harness and treated it with deoxit, and reinstalled... started Romero up (yes I name my Jeeps... Willie, Romero and TJ) the dash gauge indicated just under 14 volts and my DMM indicated a steady 13.81 volts and not a problem since... Like I said Deoxit is liquid magic. it should be in every tool kit if you deal with automotive electrical/electronics. It isnt cheap but it's worth it.
