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[andy3264]

My gearbox keeps jumping/snatching when changing up. This causes my engine management light to come on. When it does eventually change up it does so with a voilent jerk. This only happens in drive mode. My vehicle is 02 year and have hear that it could be a speed sensor, is this true.

[Auto Addict]

Welcome to the forum

What car? Engine? Year?

[Markjay]

The best thing to do with an autobox is to drop the two sumps, change the ATF (Dexron-III) and clean or replace the filter - and then see what happens. If this does not help you can continue with the diagnostic process - but many autoboxes that have been condemned were successfully revived by this simple measure...

[Kevin Wood]

If the engine management light has been on it's also worth checking both the engine and gearbox controllers for stored fault codes as that may provide a pointer.

Given that the engine light has been on, it might point to a crank / cam sensor playing up and thus giving a dodgy RPM signal to the gearbox controller. How does the engine run? Any misfires? Easy to start?

Kevin

[tunnie]

The best thing to do with an autobox is to drop the two sumps, change the ATF (Dexron-III) and clean or replace the filter - and then see what happens. If this does not help you can continue with the diagnostic process - but many autoboxes that have been condemned were successfully revived by this simple measure...

My advice would be to replace the filter, not clean it. For the sake of £40 odd cash, including sump gaskets, its worth it.

[andy3264]

Thanks for that \kevin, the engine runs ok, no misfires and no problem starting

If the engine management light has been on it's also worth checking both the engine and gearbox controllers for stored fault codes as that may provide a pointer.

Given that the engine light has been on, it might point to a crank / cam sensor playing up and thus giving a dodgy RPM signal to the gearbox controller. How does the engine run? Any misfires? Easy to start?

Kevin

[Markjay]

The best thing to do with an autobox is to drop the two sumps, change the ATF (Dexron-III) and clean or replace the filter - and then see what happens. If this does not help you can continue with the diagnostic process - but many autoboxes that have been condemned were successfully revived by this simple measure...

My advice would be to replace the filter, not clean it. For the sake of £40 odd cash, including sump gaskets, its worth it.

Not on TC, was around £60 Trade from my local Vx, the gaskets are a further £13... I seem to remember someone saying you could get pattern ones for cheap through?

[JamesV6CDX]

My gearbox keeps jumping/snatching when changing up. This causes my engine management light to come on. When it does eventually change up it does so with a voilent jerk. This only happens in drive mode. My vehicle is 02 year and have hear that it could be a speed sensor, is this true.

Project Elite had a similar problem (only with no EML...) - it had a jerky change into top gear, when booting it. Definately engine related, rather than box, because it wouldn't rev high enough to tell the box to change in sport mode.

It turned out to be that all the cam sprockets were too far advanced by a tooth (done by the previous owner, not me, I must add!) - correcting the timing fixed the problem (for about 15 minutes, until the gearbox decided to throw it's toys Thrust washers out of the pram!!)

[bigall]

ref : For  filter and gaskets  and any other parts try
Jpat automatic transmission replacement parts    
website www.jpat.co.uk                             they are based in Bristol
 for info general motors AR25/35  is  Jpats code no is 4L30E

[bigall]

Jpat's new address and phone numbers are on their website