My car goes into third gear while driving. I can be on 5th and all of a sudden it downshifts to 3rd. the car jerks and the problem only goes away after switching off the car and letting it sit for a while. this happens about once a week. I was told that this is a 'safe' mode so that the transmission doesnt get wrecked? what causes this and how do i remedy it?
Re: 1991 bmw 520i transmission goes into 'safe' mode
Quoted from BMWE34.network "
Transmission locks in "limp" mode - 3rd gear so you can "limp" home or to your nearest dealer."
"Things to check before even contemplating a transmission overhaul: Check electrics - Alternator and battery. Replace DME Relay and Fuel Pump Relay - not expensive. Remove disassemble, clean and reassemble gear selector switch - If it looks beyond saving, replace ($200) Service the transmission ($130 from a specialist) and check/replace transmission speed sensor ($90)"
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BMW has been using electronically controlled automatic transmissions in most models since the late 80s. These transmission systems employ a transmission control unit which controls electrical solenoids to manipulate the various control and shift valves and functions in the transmission valve body. When the transmission control unit detects a problem that it thinks could be damaging to the transmission or engine, it goes into a fail-safe or limp mode. In this mode, the transmission will function in reverse normally, but in forward it will operate in only one gear (whether you have the shifter in D, or any of the lower gears). This will typically be 3rd or 4th gear, depending on the model. It will start in this gear and stay in this gear with no shifting. You would experience this as sluggish acceleration and higher than normal engine speed at about 40 mph and above.
If you must drive the vehicle when the transmission is in the fail safe mode, accelerate gently and keep the road speed lower than full highway speed.
Earlier models do not employ fault codes and must be diagnosed manually. Late models do employ fault codes and a diagnostic/scan machine can be used to check and read the faults to assist in diagnostics. Note that this is not your common OBDII engine management fault code tool. This is what A BMW dealer or a properly equipped independent shop would have for full vehicle system diagnostics and coding operations.
I may have a similar issue, it's hard to tell from your description. My transmission is in 'limp' mode with a fault light on the dashboard. It basically causes the transmission to lock into third gear. Acceleration is poor because you are starting out in third gear. I'll let you know if I sort it out. It could be the switch on the brake pedal. Others have had luck switching that out
any manual transmission you shouldnt just go from 6th to 4th bc it is bad for
the transmission, if i am in 5th gear and i want to go into 3rd i always go
from 5th to 4th to 3rd as a preventative maintenance. If you have a defected
transmission you should be able to get it warranted by the bmw dealership you
bought if from though.