V8 AUTO in LIMP HOME

[Arryn Milne]

Have you checked the throttle position switch?


At 10:11 AM 11/21/00 -0800, The Quattro King wrote:
>I posted this once before:
>
>
>
>I have a friend that is working on a V8 auto that has a weird problem that
>   is stumping us.
>
>   Symptoms:
>
>   Tranny stays in limp home mode:  Only 3rd and Reverse work.
>
>   Codes:
>
>   Lost power to the TCM.  TCM seems to work though.
>   Mulitfunction switch failed.  This was replaced and the computer spit this
>   code:  Cruise Control Brake switch sorted, open or going +.  The switch
>was
>   tested and for resistance and for current and was fine.
>
>   Other symptoms:
>
>   Witht the TCM Disconnected and the key on the Cruise switch on the brake
>   pedal had no volts.  With the TCM connected it had 3.5 volts.  Is this
>   normal?
>
>   Also, should the brake light switch be sending 12V to the cruise switch
>when
>   the brake light switch is closed? My thought would be yes only to preserve
>   the memory of the cruise so that the resume function works.
>
>
>   Any ideas how to get this car out of limp home mode????
>
>
>
>
>Got one reply and tried it to no avail:
>
>
>Check to see if the brake lights are all burned out or if there is a broken
>wire to the brakes.  Audi usually uses the brake light circuit as a _ground_
>to give one extra fail safe mechanism.  Normally when you push the brake the
>CC's ground will go to something like +12v, which will disable it ... but if
>there is a problem with the connection to the lights the CC never gets a
>ground.
>
>Be advised that the instrument cluster on the V8 is set up so that if it
>thinks the tranny is in limp home mode the CC is disabled ...
>
>
>Also discovered:
>
>If the battery is disconnected, the limp home mode is reset back to normal,
>however, it comes back on as soon as the car is started.
>
>
>
>
>Someone must have more ideas.......
>
>
>
>Shayne P.
>
>
>
>1972 MB 280 SEL
>1984 4ksq
>1987 4ks
>1991 v8q5
>1991 200q Sedan
>1992 S4
>
>Parting:  1972 Mercedes Benz 280 SE 4.5