My Mum's '90 Vanden Plas Majestic is having an electrical gremlin and the trans keeps getting locked into limp home mode.

I downloaded an ebook from another forum with a number of things to try and have tried the following.

1. All fuses are good
2. Relay behind Glove box checks good
3. Check resistance on the TPS and it's good
4. Trans fluid level good with no leaks
5. No Check Engine Light

What is happening. About a month ago it started to act up and go into limp home mode while driving. Pull over and turn off engine then back on and problem would clear.
After two weeks of this the condition would no longer clear and it was stuck in limp home. I ran through the above list and it was working okay again. We swapped out for a new battery and the condition returned and would not clear.

Today I ran through the above list again and the problem cleared. I took her out for a test drive and about 8 or so miles into the drive (had made two stops as well) I was pulling out of a parking lot and thump! Back into limp home. Turned the engine off and restarted and the problem cleared. 3 miles later same thing again!

Any ideas what component is going? The car is pristine with no corrosion visible on any electrical connector and has 64K on the clock.

I see there are two more items to check behind the dash but I've run out of time for today on it....
Any help appreciated.

 

You will find the rotary switch on the driver's side of the transmission. It has 3 slotted holes (just like the enlongated holes in a TPS sensor) for adjustment. Loosen the 3 bolts enough to move the sensor and adjust until the light turns off. I can't remember if you turn left or right. Bear in mind a small move makes a big difference. I would not expect it to need more than an 1/8" of adjustment. When the light turns off, retighten botls without moving the switch.

Remember to use jack stands!!!!!!

Bad news is, it's probably on the way out. This may be only a temporary fix.

 

Ken, thanks for the time on the phone today.

Just wanted to add what I did today prior to calling you.

tried loosening the rotary switch and moving it a little (at first), then farther with no positive results. Although when I first started the car to back it out the transmission light was NOT on, but then after a restart it was.

Also pulled the cover and inspected the switch itself. Clean as a whistle but showered it with contact cleaner anyway and exercised the J gate to make sure everything got clean.

What bothers me most is there is a constant voltage drain and the lamp replace light comes on (but all lamps are functioning). Battery is brand new and if the car isn't run about every 36 hours the battery is too far down to start the engine.

I have a feeling the two issues may be related.....


Look forward to hearing from you.