42RLE Transmission – Part 1

OK, so the late model Jeep TJ/LJ’s that had automatic transmissions came with the 42RLE which some consider marginal, while most consider plain trash.  I’m somewhere in the middle, it seems to be OK, but I too have had issues.  When I first got it, it had a bad case of the ‘cold start thunk’ that a lot of Wrangler owners (especially 2005 / 2006 models) have complained about.  Sadly, I didn’t get it into the dealer in time to cover it under warranty as it presumably is just a new TCM computer module.  I’ve learned to live with it and just make my first shift nice and slow after it’s had plenty (100yds) of time to spin up in 1st gear.

But lately, I’ve also been throwing a P0846 “Pressure Sensor B; 2/4 low pressure” error which actually puts the transmission into limp home mode limiting me to 1st, 2nd, and reverse.  Had it checked out, and sure enough, there’s only 50 PSI on the 2/4 circuit so the sensor is correct but there’s low pressure – and actually, all of them are low, but the 2/4 circuit is the lowest and below the error threshold.

So first thing’s first.  Fluid and filter swap. Easier said than done.

With the UCF ultra-high skid plate, the transmission pan is not accessible anymore as it’s halfway covered by the skid plate which also holds up the entire drivetrain.  So I got to remove the skid plates and hold the transfer case in place with a jack stand – not my idea of the best way of doing things!!!

Anyway, I tried to remove the cooler lines at the cooler to not make a mess when emptying the pan, but alas, I couldn’t get the things out and simply went to plan b: make a mess and just drop the pan.  I got most of the fluid into the bucket, but alas, this is a dirty job this way and a LOT of fluid ended up being soaked up by paper towels.  I did manage to siphon some fluid out of the pan once I had it cracked a bit.

The fluid was GROSS.  Didn’t smell too awful (I’ve smelled bad transmission fluid) but it was a nice shade of dark maroon red rather than a nice bright red that new fluid is.



There was also quite a bit of gunk in the bottom of the pan around the magnet.  I’m actually a bit worried about this, but was told not to worry too much right now and that I should be good to go for a long time… we’ll see.  On the plus side, it seemed to be more sludge than metal, but there was definitely a bit of metallic stuff on the magnet.IMG_4228A

The pan itself has also seen better days, with a fair bit of dents and dings and a solid quantity of rust.


Set up an electrolysis tank and knocked off all the rust and flaking paint, then repainted it with MonstaLiner Chassis Saver Paint – the same stuff I’m using on the chassis and axles.  I really love everything about this stuff except the cost; at $40 per quart, it’s pricey!  But a little bit of work, and it’s better than new!


Because of the time I had the whole thing out, most of the fluid had drained out of the transmission, so when I put the filter back in and sealed it up, I ended up putting about 5 quarts of fluid back in.  But what a difference the new fluid makes. MUCH smoother shifting, not nearly as hard of a kick for the first gear thump, but sadly, I’m still getting the P0846 error.  Looks like I’ll be looking for more opinions on how to fix that aspect.

Also, while I had everything apart, I decided that an external filter and drain port would be really nice.  I’ll put that write up on it’s own in another post though.

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