406 Auto gearbox problem

[hei7380]

Hi guys

How do I know which gearbox (AL4 or 4HP20)is fitted on my 406 (1999 406ST, before facelifted version)?

It always jerk (after 100,000km) when changing from 1st to 2nd or 3rd to 2nd gear, does it help if changing the gearbox oil and update the gearbox firmware (it’s now 150,000km on the clock and haven’t changed the gearbox oil since new.)?

Thanks!!

[mjb]

The standard answer to any auto box problem on here is "change the oil, and make sure the level's PERFECT"

[Welly]

Yes, with any slush-matic box it is important (in my view) to change the fluid every 40,000 miles for perfect service, or every 2 to 3 years perhaps.

I wouldn't expect a fluid change to make good 100% any existing wear or damage inside the box but it can't hurt to try this first.