I just changed the transmission fluid and filter in a 2002 Jeep Grand Cherokee (yes I used the correct fluid). It now will not shift into ANY gear. The fluid level seems to be at the right place. The check engine light is now on. It was running fine before I changed the filter and fluid. What is wrong?

Check it with a code reader. This is known to happen with many cars if the fluid is not regularly changed. I do not know the exact reasons but many shops actually did not want to change my tranny fluid because of this.

Your first step is to scan the computer for codes. That check engine light is on for a reason. Get the codes and post them here and we can go from there.


That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here.

The code says: P0841 Trans Fluid Press Sensor/Switch A CKT Range/Perf

The code says: P0841 Trans Fluid Press Sensor/Switch A CKT Range/Perf

The code says: P0841 Trans Fluid Press Sensor/Switch A CKT Range/Perf

One thing to do is just go check all of the electrical connectors attached to the transmission. Visually inspect the plugs & harnesses to see if something got knocked loose or if a wire got damaged. If everything looks ok I’d be tempted to just pull all of the connectors, blow them out with some electronics cleaner, let it all completely dry out, plug it up and see what happens.

Are you sure that the new filter got installed correctly? And that you put back in about as much fluid as you got out? (at least to start with).

I second a double check of the new filter installation. I noticed in the filter install directions that the filter seal is to be installed in the pump inlet bore before the filter pipe is inserted i.e. the seal cannot be left on the pipe and the filter pulled up.

Hope that is the problem.

And was the old seal ring left in the port when the filter was installed? In any case, if the engine is run with the inlet drawing air the transmission pump will eventually fail.