K 1500 Suburban 4WD V8-6.5L DSL Turbo VIN F (1999)
Body Control Module: Reading and Clearing Diagnostic Trouble Codes
Entry Into Diagnostics
In the diagnostic mode, the BCM displays any Diagnostic Trouble Codes (DTCs) that are stored in memory. The DTCs are displayed as flash codes
through the security LED indicator lamp on the console. During normal operation, if the BCM detects a fault in a monitored system, there is no flash
code to indicate to the customer that a fault has occurred. However, the driver may detect a system malfunction. System faults are stored by the BCM as
CURRENT or HISTORY DTCs. A current DTC means that a fault was present when the diagnostic mode was entered. A history DTC indicates that the
following conditions occurred:
^
A fault occurred sometime after the BCM was installed in the vehicle.
^
A fault occurred since the last time the DTCs were cleared.
^
The fault may not be currently present.
If a current DTC is stored, the associated history DTC will always be stored.
When working on systems that are controlled by the BCM, the technician should always refer to this section and check for DTCs.
Enter diagnostics by performing the following steps:
^
Turn the ignition switch to the RUN position in order to disarm the universal theft deterrent system, if equipped.
^
Turn the ignition switch to the OFF position.
^
Remove the RADIO fuse 17 from the instrument panel fuse block.
^
Turn the ignition switch to the ACC position. This action will enter the program mode. Two audible warning tones will occur for mode
verification.
^
Within 5 seconds, turn the ignition switch to the OFF position. Immediately (within one second) turn the ignition switch back to the ACC
position. This action will enter the diagnostic mode. Three audible warning tones will occur for mode verification.
The BCM will begin to flash DTCs 4 seconds after entering the diagnostic mode. Each flash of the security LED indicator lamp on the console
represents a number. For example, one flash followed by two quick flashes represents a code 12. Each code is displayed 3 times before the next code is
displayed. Stored DTCs are displayed in numerical order. Once the last code is displayed, the list begins over again with the first code. The display
continues until the diagnostic mode is exited.
While in the diagnostic mode, a transition of certain BCM inputs from active to inactive, or vice versa, will cause the BCM to actively respond. For
example, if a door lock switch is depressed the BCM will perform the following actions:
1. Flash the FASTEN SEATBELT indicator.
2. Sound a single audible warning tone.
The BCM will also respond in the same way if the rear compartment lid or a door is opened or closed. This is due to the transition at the door jamb
switch or the rear compartment lid ajar indication switch input. In all cases, the BCM will also attempt to perform the operation normally performed by
the switch transition.
The BCM will also respond to a change at either the shock sensor tamper input or the shock sensor shock input. The tamper input is activated by minor
blows to the vehicle. The shock input is activated by heavy blows to the vehicle, or by tapping on the exposed shock sensor. In the diagnostic mode, if
either the tamper input or the shock input becomes active the following actions will occur:
^
The BCM will activate the horn relay.
^
The horn relay will cause the horns to chirp.
^
The BCM will sound an audible warning tone.
Any transition at the interior lamps command input while in the diagnostic mode will cause the BCM to perform the following actions:
^
Flash the FASTEN SEATBELT indicator lamp.
^
Sound an audible warning tone.
^
Flash the courtesy lamps.
The above actions can be caused by such transitions as switching the interior lamps switch to the ON or OFF position.
DTC Display Order
In the diagnostic mode, diagnostic trouble codes (DTCs) are displayed in numerical order. The first DTC displayed is always DTC 12, followed by any
current DTCs (21 to 24) or any history DTCs (31 to 34). Remote control door lock transmitter diagnostic DTCs (41 to 45) will then be displayed if
activated while in the diagnostic mode.
The last DTC displayed is the begin configuration display (55). The first number following DTC 55 is the hardware configuration. The second number is
the software configuration. DTC 55 and the 2 configuration numbers are always displayed. After the configuration numbers are displayed, the entire list
is repeated beginning with DTC 12. System faults are stored as current or history DTCs. When working on systems controlled by the body control
module, always refer here and test for DTCs.
Clearing Diagnostic Trouble Codes
