Hello all,

I have a 2002 TJ Magna 3.5L Auto.

Got it serviced about 6 weeks or so ago, was fine until Saturday night, when it went into limp home mode. Got it to a different mechanic yesterday without driving it. He said the wrong Trans Fluid was used and said we could possible save the transmission by flushing it as the oil didn't seem to have burnt.

Calls me the next day says it's good, he flushed it repeatedly and now it drives. I go pick it up and drive it home where it sits for about 4 hours. Go to drive again and it is back in limp mode. Leave it for another 2 or so hours as I need to go to dinner and check it again when I get home and it's still in limp mode.

I don't know if it matters (I've seen people mention rain before) but on the way home from the mechanic it absolutely started pissing down, insane rain.

Any suggestions or ideas as to why it would drive perfectly fine and then go back into limp mode?

I apologise in advance if I haven't followed the correct format.

Still have the plastic splash guards under the front of the car? If not, check the two speed sensors on top of the gearbox for wetness.
They have electrical wiring connected to them, so they are easy to spot.
Any moisture in the connectors tends to upset the gearbox.

When you said wetness, made think water leaking on tcu, made me think leaky capacitor.
That can cause (faulty TCU, which can be intermittent) limp mode. Can that be determined in stored fult codes? Visual inspection?

put dielectric grease on the connector's it will stop water and moisture getting in

Wrong fluid will not cause limp mode, only an idiot of a mechanic would even suggest that

Issue is electrical OR it is internal where the output and input shaft sensors are either not working or are out of range to each other.

Most issues stem from leaking heater core and the TCU part of the ECU get wet and signals get crossed then you will have an issue with limp mode. Also trans relay, (a single relay usually attached to ECU bracket) can get wet and stop working as well

Wrong fluid will not cause limp mode, only an idiot of a mechanic would even suggest that

Issue is electrical OR it is internal where the output and input shaft sensors are either not working or are out of range to each other.

Most issues stem from leaking heater core and the TCU part of the ECU get wet and signals get crossed then you will have an issue with limp mode. Also trans relay, (a single relay usually attached to ECU bracket) can get wet and stop working as well

I don't know what much of this means but I'll pass the message on. I did find out today that the heater is also busted, which I guess is the heater core (I'm a computer guy, have bare minimum knowledge when it comes to cars) so you're probably right.

When I say it's busted, apparently needs to be re-gassed or something (requiring the dash and radio to come off) as it leaked, which is the ECU you're referring to?

Also as per the trans fluid, he thought it may have burnt out the trans. Don't know how he got it to drive after flushing it 3 times.

The heater is leaking, the ECU sits below it, is most likely wet and thus is giving issues

Thank you folks, it was what you said, moisture in the ECU.

How much did it cost to get fixed?

I got heater core pipes, seals and air conditioner service done in SA for $550.

Other places wanted $1000.

Where was that? That's a good price for an entire day's labour.