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2007 Jeep Liberty strange PCM issue
http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=45&t=82588		 Page 1 of 1
Author:  jasonc [ Sun Jul 12, 2015 12:34 am ]
Post subject:  2007 Jeep Liberty strange PCM issue
I've been doing work on my sisters Jeep Liberty and have hit a major bump with repairs. I was going to take some readings with a scanner when it displayed that it could not establish communication, however,this was working the day before. I also noticed that with the ignition in the accessories position all the lights on the instrument cluster illuminate but the SKIM indicator light remained lit. I decided to put these issues to the side for later and focus on some other repairs. Here's where it get's weird, at least for me. I left the key in the acc position and while under the hood trouble shooting the fuel pump relay I jumped position 30 of the relay to position 86. As soon as I did that the car energized all the items it normally energizes when in the acc position such as the fuel pump, asd relay, etc. I also noticed on the instrument panel the SKIM indicator light turned off and I could communicate with the PCM again through the OBD port. However as soon as I remove that temporary jump in the cavities of the fuel pump relay it goes back to the way it was before with no communication. As far as readings go with the OBD the only code I have at the moment is for the MAP sensor. This makes sense, since I had it removed to replace it. I've looked through the wiring diagrams but I'm not having much luck with them. The only info I have so far about the relay is 30 supplies constant voltage and 86 is the fused ignition switch-output run-start. Can anyone else offer some guidance ? Thanks !
Author:  WWDiesel [ Sun Jul 12, 2015 10:11 am ]
Post subject:  Re: 2007 Jeep Liberty strange PCM issue
Simple, you are backfeeding 12v + from terminal 30 to 86. 30 is the battery 12v+ and 86 is the ignition circuit. :wink:
see diagram:
Image
Author:  jasonc [ Sun Jul 12, 2015 12:32 pm ]
Post subject:  Re: 2007 Jeep Liberty strange PCM issue
Well that makes perfect sense then, thanks. So where would be a good point to start troubleshooting ? I removed the ignition switch harness to inspect the actuator pin and all seems good. While I had the harness off I tried turning it with a screw driver but still the same result. I've tested the B+ points on the harness as well and the voltage is good. Im guessing it's a wiring issue from the harness to the PCM. Looks like I'll be tracing this out.
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