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Voltage meter - Transmission slip NEED HELP

Tomynoks

NAXJA Forum User
Location
Mesa, AZ
'99 XJ- first symptom was that the voltage meter maxes out after running a few minutes... then the transmission slips.. won't move in D--- will move in lower gears. PCM threw code of P0715 Speed sensor-- replaced that.. same symptoms.. I assume it threw that code becasue the tranny is slipping....put in another PCM..(voltage reg is on PCM) no change. The transmission only slips when the voltage maxes out. It seems fine when it's at 14v. Also tested volage at battery w/ engine running.. it is at 19-20v.

Need some help badly...

Thanks,

Tom
 
First thing I'd check is the grounds to the engine block and alternator. I also wonder if there's a bad diode in the alternator causing odd voltage spikes. Also make very sure that your battery connections are good and that your battery itself is good.
 
I'm thinking bad engine-battery ground as well. High resistance there would drop the voltage going to the tranny solenoids and it'll act like the tranny computer is bad (ie gives you 4th gear with shift in D).

If you have a voltmeter, you could check the voltage between the block and the battery neg terminal with the engine running. Anything more than a tenth of a volt and you should be looking at the ground cable.
 
Nope. That's not it. I wish it was. Volt meter reads ZERO between neg term and block. Took off ground cable and brushed contacts to be sure.

ANything else you can thing is greatly appreciated!

Thanks,

Tom
 
Ok..... It was the ground strap off the rear of the block to the firewall. I decided to clean anything that was grounded inside the engine compartment, one at a time and check to see if there is any change. The last one I checked was the rear ground strap and that was it. Simple huh? Didn't cost a dime. I also know that at least as of right now, my alternator, PCM and speed sensor are all working fine. Thanks for the help, I hope this will help someone down the road.

Tom Smith
 
Good. Sorry I forgot to mention that one. I should have, because it's a known failure spot, and I've had one fail myself. Here in rust country, it can look good until you touch it, and then you realize that it's turned to powder.
 
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