TWILIGHT SENTINEL & THEFT DETERRENT OPER. DIFFERENCES

SUBJECT: TWILIGHT SENTINEL AND THEFT DETERRENT OPERATION DIFFERENCES

MODELS AFFECTED: 1990-1992 DE VILLES, FLEETWOODS, AND BROUGHAMS

This bulletin supersedes T-90-72 which should be discarded. It is being revised to include new part numbers and additional system operation differences.

Some 1990-1992 De Villes, Fleetwoods, and Broughams with option code T82 may exhibit one of the following conditions:

1. With the twilight switch on or off, in dark ambient conditions, key off:

A. When the park lamps only are turned on, the headlamps will turn on for the delay set by the twilight control switch then turn off. With the twilight switch off, the headlamps turn on for the minimum delay when the park lamps are turned on.

B. When the theft deterrent is activated, the headlamps will turn on. The headlamps and park lamps will not flash. The horns will sound on and off normally.

2. With the twilight sentinel enabled in dark ambient conditions, when the ignition is turned off, the headlamps will turn off when either the driver's door is opened or the brake pedal is depressed. The twilight delay is cancelled and the headlamps appear to time out early.

3. The lights cycle on and off at dusk or on overcast days when set in twilight mode.

4. The lights will turn off only at high light intensity levels. Complaint: Lights remain on too long as morning light increases after dawn.

5. The lights time out in less than 90 seconds after key off when the delay switch is set at maximum delay. Service modules marked with a black X on the lower left hand corner of the yellow label have incorporated changes to ensure a 90 second delay time. These modules must be used to repair this condition.

To repair any or all of these conditions, replace the twilight sentinel module with GM Service P/N 16518842 . Refer to Service Information Manual, Section 9C, for replacement procedure.

Parts are currently available from GMSPO.

WARRANTY INFORMATION VEHICLE SERIES -------------------- -------------- Operation Operation Description Number C D E K V --------------------- --------- --------------------------- 1990 R4220 .9 .3 1991-1992 R4220 .8 .3

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.