AW4 troubleshooting

[Cn1626]

Hi all, I’m new to the forum but not so new to the XJ community. I have a 01’ Cherokee limited that I picked up recently and it runs like a dream. I’ve never had any reason to be concerned with it until recently when the CEL came on. I ran the code and it was P0751. This is telling me it’s the number one solenoid malfunctioning or sticking. When I got this code I also lost OD. I’m getting ready to pull the pan and replace the solenoids but I figured after reading up on similar situations I’d ask if anyone has ever run into this same problem and how they were able to fix it. The part that is so confusing to me is that even with the loss of OD the trans shifts super smooth through the gears. That to me says I may have something else causing this issue other than the number one solenoid. Any help would be greatly appreciated.

 

[75SV1]

You can check the solenoids from the engine bay. One of the plugs up by the trans dipstick tube. I forget if it is the Black or the gray plug. There is info around on that plug and pins. 3 of the 4 on top are to the solenoids. Ohms should be 11 to 16 ohms. One probe to the pin, the other to a ground on the chassis or engine block. If they check OK, I'd change trans fluid a couple of times.
Also, there are two speed sensors on the 98-01 trans. I did have one go bad. It did affect gear shifting. Still, check the Ohms and if OK, I'd change fluids.

 

[lawsoncl]

I forget if it is the Black or the gray plug. There is info around on that plug and pins. 3 of the 4 on top are to the solenoids. Ohms should be 11 to 16 ohms. One probe to the pin, the other to a ground on the chassis or engine block.

 

[Cn1626]

Thanks for the info, I’ll test the solenoids tomorrow night and give an update. The fluids were all changed recently I had the thought that it may just be all buggered up so I did the new pan, screen and gasket at the same time. It did run a bit better but didn’t resolve the CEL. The one thing I did not think of is the speed sensors I’ll have to look into those as well.

 

[lawsoncl]

Thanks for the info, I’ll test the solenoids tomorrow night and give an update. The fluids were all changed recently I had the thought that it may just be all buggered up so I did the new pan, screen and gasket at the same time. It did run a bit better but didn’t resolve the CEL. The one thing I did not think of is the speed sensors I’ll have to look into those as well.

The speed sensors almost never go bad, and on a 2001 they should throw a code. The front will just throw a code if bad, whereas the rear output will cause it to not upshift. The two sensors are identical, btw.

 

[Cn1626]

Finally got to testing the solenoids, solenoid one tested at only 7.25 and 2&3 were up about 10.25. Looks like I’m going to pull the pan replace the solenoids and see what happens from there. I noticed this week that she’s running a little hot like 220ish I’m wondering if my trans issue may have something to do with that as well.

 

[lawsoncl]

Finally got to testing the solenoids, solenoid one tested at only 7.25 and 2&3 were up about 10.25. Looks like I’m going to pull the pan replace the solenoids and see what happens from there. I noticed this week that she’s running a little hot like 220ish I’m wondering if my trans issue may have something to do with that as well.

Possibly, if the t/c solenoid isn't locking up.

 

[Cn1626]

So finally after a long week I’ve gotten in the trans and replaced the solenoids. I have all 4 gears now and all of the solenoids tested at 11.42ohms before I put it all back together. So that one solenoid that tested at 7.— is gone. I’m almost certain the TC isn’t locking up after the new solenoids are in and my CEL has stayed on with the P0751 code. Thoughts ?

 

[lawsoncl]

You cleared the codes and it came back? The test for the t/c lockup is drive along on the highway at a steady speed and lightly tap the brake with your left foot. You should see the rpm jump up a few hundred rpms.

 

[Cn1626]

Yes, cleared and came back, same code. It was an emergency day today, had to take the gas tank down and replaced the fuel pump. Once I get out again tomorrow I’ll try the TC test and report back.

 

[Cn1626]

Well I got out and drove around this morning, cleared the code again before I left. Back on within 15 minutes. Tested the TC lockup and it is doing just fine. So now after replacing the solenoids and testing them I’ve also confirmed that the TC is locking up but I’m still getting the P0751 code that says solenoid A Performance/ stuck off. I’m starting to think I may need to replace the TCU and try again. Possible electrical problem or perhaps the valve body? Any and all help at this point is greatly appreciated.

 

[Cn1626]

To add to the last post, I have checked the solenoids again at the harness in the engine bay. Where they were reading 11.42 on Saturday they now read between 10.42 and 10.56. I’m not quite sure why this would change over a couple of days.

 

[Rob Mayercik]

Could there be a damaged wire between the engine bay and the TCU? Not sure if the TCU "senses" the solenoids based on what it commands, or if there's separate "readback" lines...

 

[lawsoncl]

Resistance can vary a bit with temperature. The bad solenoid codes can come from sensing the electrical side, or on the 98+ by comparing the input and output shaft speeds.

 

[Cn1626]

I’m going to have to inspect all the wires from the harness back to the TCU. I’m also wondering if there may be a damaged wire internally in the trans. Although that gets a little more involved. I’m going to try a new TCU this weekend I have a buddy that has an 01’ like mine and we are going to swap out the TCU and see if that makes any difference as well. I’ll look into the “ read back lines” and see what I can find out, it may just be worth it to replace the whole harness from the TCU to the trans with new and know that’s all out of the equation.

lawsoncl I’m not quite sure what you mean by “ sensing the electrical side.” I’m far from an electrical kind of guy but I’m learning my lessons on this one. Mechanical no problem, electrical and I go cross eyed. Thanks for the help!

 

[75SV1]

A few things. First battery volts. Second the trans is controlled or receives info from at least 5 sensors. ECM, TCU, TBS, NSS ( Range Selector for 98+), Brake switch.
The NNS is easy to clean or recondition. The main issue is getting off the trans.