jeepxj19

So I have been having a problem were the CEL will come on and with throw the code po758? For a problem with the shift solenoid, I went on vacation, so I didnt have time to check it out myself so I left it at a tranny mechanic, he said he tested all the solenoids and they tested fine and he said he checkd some thing with the wireing harness and now is telling me I need to replace the ecu to fix the problem. Any thoughts on this? To me it doesnt sound right, I think its just the solenoid on its way out

excess650

Do you have any have any symptoms other than a CEL?

There are (2) shift solenoids S1 and S2, and a lockup solenoid S3. The trans is controlled by the TCU which is seperate from the ECU. The TCU has inputs from the TPS, VSS, and brake pedal switch.

jeepxj19

No not rlly, sometimes when the CEL comes on, it feels like my rig is taking off in 2nd, but if I manually shift it (by putting it into 1-2) then into drive it runs fine, once the CEL goes out it runs completely normal. Iv nvr had a problem with the tranny

excess650

It sounds like your S1 solenoid may be going out. My '96 started out that way, ocassionally not downshifting to 1st, and gradually got worse. At the time I simply pulled it down to 1-2 and pulled out and then upshifted to 3 and D. As time went on I noticed that it wouldn't downshift to 2nd when hard on the throttle, and later, it would never select 1st when put into D or even 3. At the same time I noticed that it didn't like to stay in OD or lockup, so I started searching the 'net and ended up here.

After researching and troubleshooting, I narrowed the problem to either the S1 solenoid or the wire from the TCU to the S1. When I dropped the pan and disconnected the connector, I was able to confirm that the solenoid was completely whacked. 12-18 ohms is ''normal" when warm, but mine was more like 18K ohms.

I replaced the S1 with an OEM sourced from Jeep. Their price was similar to Napa and Autozone, but it was OEM. Their are less expensive solenoids, but I was warned by a local trans guy that the bargain brand often fail in a month or two.

There are other folks who had similar symptoms to mine, but ended up being a TPS. Lucky for them, its $40 and easy to reach.

In that you're actually getting a CEL and code indicating a solenoid ( I didn't get either with OBD II) its more likely the S1 solenoid than a sensor.

Drain the fluid, drop the pan, and change the middle solenoid on the driver's side. There is a bolt on the passenger side front of the bellhousing that holds the dipstick tube in place. If you remove it, you can drop the tube with the pan far enough for access. Your exhaust may be in the way and prevent fully droppping the pan, but again, enough room for access. There won't be a gasket, so you'll have to remove the old RTV, clean the surfaces of the trans and pan, and use RTV again. The solenoid has (1) 10mm bolt holding it, and (1) electrical connector. Remove, replace, button up and refill with 4-1/2-5 quarts of Dexron III/Mercon. Be sure to bolt the dipstick tube back to the bellhousing.

jeepxj19

Thanks for that info, yea tomorrw im gonna replace the solenoid, and hopefully that does the trick

greengoblin

i had one do that to me. only did it when the tranny was up to temp. if the sol. was not the problem you wouldnt need a new ecu you would need. the transmission control module. but i changed all three of the sol. and i have not had the problem since and while your in there change the filter and gasket while your at it.

CoffeeCommando

Would something like this cause it to not start at all? Mine started sputtering and died on me as I slowed to pull into a gas station. I had P0740, TCC malfunction.

And where IS the TCU?

Freemansxj

Here is a write up I did over on naxja for those with solenoid problems and replacement. Hope it helps.

http://www.naxja.org/forum/showthread.php?t=987463

John