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Matt, Engineer
Category: BMW
Satisfied Customers: 20396
Experience:  Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
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My 1991 BMW 850i will not take the trottle, when I

Customer Question

My 1991 BMW 850i will not take the trottle, when I accelerate the power drops and the computer says "Trans Fail-Safe prog". I can drive it then at a slow speed. If I turn off the car and then start it again the error will be gone bt when I accelerate it happens again.
JA: How old is the transmission? Have you checked the fuel filters?
Customer: The transmission is the original 1991 but there is only 40 K miles on the car. I have not checked the fuel filters. Could they be responsible for that fault?
JA: Are you fixing your 850i yourself? What have you tried so far?
Customer: I have brought it to a garage where it was diagnosed with an error on the cam sensors however both of these were replaced with no improvement.
JA: Anything else you want the mechanic to know before I connect you?
Customer: Lately the batteries go down when the car is not used and need recharging.
Submitted: 2 months ago.
Category: BMW
Expert:  Matt replied 2 months ago.


I'd take a look at the colour of the transmission oil it should be a dark red colour if its black then its needs changing together with its oil filter. Also check its level with the gearbox warm and just after you've moved the selector through all the positions leaving it for a few seconds in each one and then back to park.

You can top up the box through the dipstick tube if required and make sure you use the correct oil for your car as the fluids are not all the same. Some manufacturers recommended a change of the type of fluid - Speak to the local dealer and parts dept - they will advise you on the updated fluid to use..

If that’s all OK then check all the electrical connections of the gearbox, remove each connector in turn and spray with contact cleaner. Check that the wiring to the gearbox is in good condition with no chafing or frayed wire

If this is OK then check the selector lever linkage / cable under the car for any broken parts and or missing bolts as if this is coming adrift then it can rub on the car body or just bind up

Then - you should top up if low and re try it - or, if its level is ok - and condition is ok - then the next step is to drain it off - open it up and clean the filters inside -- refill and retry it..

Expert:  Matt replied 2 months ago.


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