"Differential" Diagnosis (Pun Intended) - JeepForum.com
 
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post #1 of 5 Old 12-13-2015, 11:53 AM Thread Starter
OkieSully
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"Differential" Diagnosis (Pun Intended)

Hello! We've got a 2007 Commander with QDII and a recent "Service 4wd System" message. The message popped up after the car was detailed (carpets got really wet) and we experienced a bunch of electrical problems (no radio sound, no seat heaters, jumpy gauges, and the much dreaded "Service 4wd System" message). We've got everything sorted out except the seat heaters and the 4wd. I've tried the Fuse No. 25 trick, but it didn't work.

We took the car into the dealership to have a recall performed on Friday (hoping that it would resolve the message). No dice. They didn't scan it, but offered to pull the codes for about $150. Before I shell out the bones to get the scan, I was hoping someone could offer a differential diagnosis on whether the problem is with the front/rear differentials, or with the transfer case actuator.

I checked voltages and resistances at the transfer case and FDCM plugs and it looked okay (at least I've got 5V to the transfer case actuator). I checked continuity at the FDCM for the front and rear differentials and didn't find open circuits. Any way to tell if it's the transfer case motor or a solenoid in one of the diffs?

Thanks!

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post #2 of 5 Old 12-13-2015, 01:24 PM
Hemicuda61
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The first thing I would do is replace the battery if it is old. These vehicles go nuts with electrical issues if the battery voltage drops.

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post #3 of 5 Old 12-13-2015, 03:05 PM Thread Starter
OkieSully
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Thanks for the response - I thought that might be the issue and had the battery checked (it's only a couple months old and still good according to the parts shop). I threw it on the charger last night and it didn't seem to fix the problem. Here's a little additional information in case it helps. The "Service 4wd System" message comes on as soon as the ignition is turned to "on." When I try to engage 4-Lo, the message will reappear and I don't hear the transfer case motor/actuator doing anything. So, I guess I'm looking for any thoughts on whether the transfer case motor would still activate if the problem was a broken/frozen solenoid in one of the differentials. If so, I think I can narrow this down to the transfer case actuator. If a broken differential solenoid would also shut down the the transfer case motor, I guess I'm still looking at multiple potential issues. Thanks!
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post #4 of 5 Old 12-13-2015, 05:26 PM
Medic80
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"Differential Diagnosis" - good one

Medic80|05 Larado|Black Crystal Pearl|4.7L|1.5" RC's|Saharas|255/60/18 KL61 AWT|Black WK Member 79
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post #5 of 5 Old 12-13-2015, 09:10 PM
Hemicuda61
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Take it to a dealer and ask for P73 Flash update. That should take care of the "Service 4WD" message.

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service 4wd system , solenoid assembly , transfer case

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