Possible Causes
(A103) FUSED B+ CIRCUIT
(Z429) BRAKE LAMP SWITCH GROUND CIRCUIT OPEN
BRAKE LAMP SWITCH
(B29) BRAKE SWITCH NO.1 SIGNAL CIRCUIT OPEN
(B29) BRAKE SWITCH NO.1 SIGNAL CIRCUIT SHORT TO GROUND
PCM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE -
DIAGNOSIS AND TESTING)
Diagnostic Test
1.SCAN TOOL DOES NOT SHOW BRAKE SW PRESSED OR RELEASED
Ignition on, engine not running.
With the scan tool in Inputs/Outputs, read the Brake Switch state.
While observing the scan tool display, press and release the brake pedal several times.
Does the scan tool display Brake Switch PRESSED and RELEASED?
Ye s>>
The Brake Lamp Switch is operating properly at this time.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)
No>>
Go To 2
2.(A103) FUSED B+ CIRCUIT OPEN
Turn the ignition off.
Disconnect the Brake Lamp Switch harness connector.
Using a 12-volt test light connected to ground, probe the (A103) Fused
B+ circuit at the Brake Lamp Switch harness connector.
Does the test light illuminate brightly?
Ye s>>
Go To 3
No>>
Repair the open or short to ground in the (A103) Fused B+
circuit. Check and replace fuses as necessary.
Perform the POWERTRAIN VERIFICATION TEST. (Refer to
9 - ENGINE - STANDARD PROCEDURE)
