Electrical problems

BWPEPPERS

MEMBER
2004 CHEVROLET SUBURBAN
186 MILES

With my Z71 SUV shut down, ignition switch off, the rear window wiper comes on even with the rear window wiper switch in the off position.
While driving at night the headlights will shut off with the headlight switch in the “Auto” position. Cycling the switch off then on will turn headlights back on.
Drivers side door unlock switch works intermittently. Passenger side door lock switch works normally.
Drivers side seat heater will turn on randomly while the switch is in the off position.

1 Reply

ASEMASTER6371

MECHANIC
52,797 POSTS

Good morning,

The one thing that all these components have in common is the body control module.

It is very possible you may have a bad connection or the actual module is the issue. If you have a scan tool, you could monitor the operation of the module and see if any codes are stored in the module.

It is under the drivers dash. I attached a picture for you to view.

Roy

Description and operation

Body Control Module (BCM)
The body control module (BCM) monitors several inputs in order to arm and disarm the CTD system. The BCM controls the alarm function outputs. When the BCM detects an unauthorized entry (any door opened), the BCM applies ground to the horn, the park lamp and the headlamp relays. The BCM will send messages to the security telltale in the instrument cluster through the Class 2 serial data link. The BCM has the following 8 basic modes for operating the CTD system. The more detailed descriptions are below.
- Off state
- Idle state
- Disarmed state
- Ready-to-arm state
- Arm initiated state
- Arm delay state
- Armed state
- Alarm state

The BCM has the following 6 discrete inputs in order to monitor the CTD system:
- Ignition 1
- Driver door latch (door jamb) switch
- Passenger door latch (door jamb) switch
- Door lock relay
- Door key switch
- Passenger door unlock relay

The BCM applies ground once per second for approximately 2 minutes, or until a valid input to disarm the system is received by the BCM.

VEHICLE THEFT DETERRENT (VTD)

Body Control Module (BCM)
The Body Control Module (BCM) contains the theft deterrent system logic. The BCM reads the Passlock(TM) data from the Passlock(TM) sensor. If the Passlock(TM) data is correct, the BCM will pass theft. The BCM will then transmit the fuel continue password to the VCM/PCM.

During the tamper mode the vehicle may start. The vehicle will then stall. If the BCM receives the wrong Passlock(TM) data, the VTD will immediately go into the tamper mode. The tamper mode will lock-out the vehicle fuel injectors for 10 minutes. The SECURITY indicator will flash while the VTD is in the tamper mode.

If the Passlock(TM) sensor sends a correct password to the BCM when the ignition is in the ON position, the BCM will send a fuel enable signal to the VCM/PCM. The VCM/PCM will not disable the fuel due to any BCM message for the remainder of the ignition cycle.

Image (Click to make bigger)