How do you check your PCM to see if it has gone partially bad?

electriczipper · 07-05-2011, 06:21 PM

Hi, I was wondering how to check out the pcm? I've a problem that has us stumped, and before replacing the whole fuel pump module it would be nice to check out the pcm to make sure it isn't the whole problem. I posted the question below earlier, and her it is to give you some idea as to where we are at. The jeep starts and runs now after sitting 3 mnths but the Snap-on Modis code PO463 keeps coming up but there hasn't been any problem with the fuel gauge. I'm guessing that the snap-on code is the equivalent of the hex code 96.

Hi all,
I've a 96 cherokee classic 4.0 L that was occasionally spitting, and sputtering on the way to work one day, and it wouldn't start after work. There was no power to the coil. Found a fuse in the PDC that was blown, #6 slot, 30 amp big fuse. Replaced it, and it spit, and sputtered a little on the way home. Made it home, shut it down, and it wouldn't start, it had blown the fuse again, and again. Diagnostic Trouble code #42 came up after cycling the key switch 4 times. Here is what is listed for MIL code #42.

Hex code 65/ Fuel Pump Relay Control Circuit/ An open or shorted condition detected in the fuel pump relay control circuit. or

Hex code 0A/ Auto Shutdown Relay Control Circuit/ An open or shorted condition detected in the auto shutdown relay circuit. or

Hex code 2C/ No ASD Relay Output Voltage at PCM/ An open condition detected in the ASD relay output circuit. or

Hex code 95/ Fuel Level Sending Unit Volts Too Low/ Circuit shorted to ground between PCM and fuel gauge sending unit. or

Hex code 96/ Fuel Level Sending Unit Volts Too High/ Open circuit between PCM and fuel gauge sending unit. or

Hex code 97/ Fuel Level Unit No Change Over Miles/ Sending unit reads too long.

The #6 slot 30 amp big fuse in the PDC is for the Power train control module, Transmission control module, & the Fuel pump relay.

The Cherokee has 246 thousand miles on it same with the fuel pump, and I was thinking maybe something in the fuel pump module.

wheelin · 07-05-2011, 06:40 PM

how long does it take for the fuse to pop? If it blows as soon the the key is turned on then start to unplug componets one at a time, until fuse doesnt pop.

electriczipper · 07-05-2011, 06:56 PM

It doesn't blow now. It was doing it right at the attempt to start it back in February though.

Thanks

**CJ7-Tim** · 07-05-2011, 07:50 PM

P0463 (M) Fuel Level Sending Unit Volts Too High. Circuit shorted to voltage between PCM and fuel gauge sending unit.

You have a blown fuse, and a CEL codes for a short circuit. Seems to me, you have a wiring fault between PCM and fuel gauge sending unit.

What leads you to believe that the PCM is faulty ? OBD-II four digit trouble codes are much more specific about the faults than two digit OBD-I generic fault codes. Your Jeep is trying to tell you what is wrong.

electriczipper · 07-06-2011, 07:26 AM

Took it to 2 shops to have the codes read. No luck there as OBD II couldn't read it, it had trouble communicating with the pcm, it pulled up nothing, and the chrysler code reader couldn't communicate with the PCM, but a Snap-on Modis was able to come up with the P0463 code. Fuel gauge still works so it has me stumped as to what is definitely wrong but will start with the fuel pump assembly, and see if it does more than just lighten the wallet.

electriczipper · 07-23-2011, 09:45 AM

Got a n.o.s. pump assembly from the jeep hut, they weren't kidding about their statement "some oxidation may have occurred during shelf life" but it functions just fine, and the trouble code hasn't reappeared after installation, and erasure of the trouble code. I hope this was the end to that fuse blowin.

ez