BMW E39 automatic transmission in limp mode
Why does the E39 automatic transmission go into limp mode?
Limp mode is indicated by a yellow gear symbol light or the message transmission fail safe mode. The cause can be a weak battery, a failed transmission control module or an internal transmission fault, for example a broken drum. Start by reading the fault codes.
What should I check first when the automatic transmission limp mode light is on?
Check the battery and alternator: a weak battery has triggered the limp mode light, and replacing the battery fixed it. If the ABS and DSC lights are also on in the cluster and the speedometer does not work, check the ignition switch base, because it can cause strange problems.
How can I tell the fault is inside the transmission?
Metal flakes or powder in the transmission oil point to damage to the torque converter (turbine) or another internal part. In that case the transmission should be repaired before it fails completely. A rattle only when warm can be caused by foaming oil. Leave internal faults to be diagnosed by a shop experienced with automatic transmissions.