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Old 07-12-2010, 03:13 PM
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Weird Transmission Downshifting

I posted in the Troubleshooting forum as well but no repsonses so apologies in advance for double-posting here:

I have a 2005 WK Grand Cherokee, 4.7L

The tranny is doing an odd thing fairly regularly. I'll be driving along at 60mph or so and it will shift out of overdrive. Sometimes it feels like it's even kicking down into 3rd. Then just as suddenly, it'll go back to normal.

I've replaced the TPS and both input/output speed sensors on the transmission. The only DTC being thrown showed the right rear wheel speed sensor was indicating "implausible distance" so that's been replaced too.

I replaced the TPS and the I/O sensors myself but I saw a note in the service manual that indicates an ETC Relearn is needed after TPS replacement which sounds like a trip to the dealer.

Just to add to the fun, I've recently gotten two intermittent "SERVICE ELEC BRAKE SYSTEM" messages. Not sure if this is related or not.

Thoughts or suggestions?
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Old 07-12-2010, 04:30 PM
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Re: Weird Transmission Downshifting

service elec brake is USUALLY a sensor.

trans sounds like ESM but not popular for the 4.7's. but thats where I would look.
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Old 07-12-2010, 08:19 PM
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Re: Weird Transmission Downshifting

If the tranny temp is to hot it will downshift out of overdrive but you shold get a Transmission over temp" Display though
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Old 07-13-2010, 07:37 AM
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Re: Weird Transmission Downshifting

Thanks guys. I'm not getting any overtemp DTCs. Also, the PRND display looks normal ("D" still displays the whole time). Would an ESM issue show up on the gear display?

On the brake system, is there a way to see trouble codes in that module with anything other than a Chrysler DRB scanner?
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Old 07-20-2010, 03:14 PM
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Re: Weird Transmission Downshifting

I finally threw in the towel and took it to the dealer... twice. The first time they couldn't replicate the issue but saw a DTC for a rear wheel speed sensor which they replaced. Unfortunately, that didn't solve the problem.

The second time to the dealer they were able to replicate the problem. The tech thinks it's the PCM and, amazingly, they say this is covered under the emissions warranty. It's going to take a few days to get the new PCM so we'll see how that goes.
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Old 07-20-2010, 03:17 PM
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Re: Weird Transmission Downshifting

good luck, report back please. thx
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Old 07-25-2010, 09:39 AM
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Re: Weird Transmission Downshifting

Well it's fixed I think. The PCM swap didn't solve the problem. The dealer ended up changing the TPS and that appears to have taken care of it. That's a bit weird since I had already replaced the TPS but I suppose it could have developed an issue.
Either way, things have been running much better for the last few days. Now on to some Bilstein struts and shocks!
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