Re: Low Voltage Brake Switch Grand Prix

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Document ID# 574942

2000 Pontiac Grand Prix

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DTC C0161 ABS/TCS Brake Switch Circuit Malfunction Circuit Description The Stoplamp Switch is a normally open switch, when the brake pedal is depressed, the EBTCM senses battery voltage. This allows the EBTCM to determine the state of the brake lamps.

Conditions for Setting the DTC

EBTCM detects battery voltage at all times. EBTCM never detects battery voltage from CKT 17. Both brake lamps are faulty.

Action Taken When the DTC Sets DTC C0161 is set. ABS and TCS remains active.

Conditions for Clearing the DTC The condition responsible for setting the DTC no longer exists and the scan tool Clear DTCs function is used.

100 ignition cycles pass with no DTC(s) detected.

Diagnostic Aids It is very important that a thorough inspection of the wiring and connectors be performed. Failure to carefully and fully inspect wiring and connectors may result in misdiagnosis, causing part replacement with reappearance of the malfunction. Thoroughly inspect any circuitry that may be causing the complaint for the following conditions: Backed out terminals Improper mating Broken locks Improperly formed or damaged terminals Poor terminal-to-wiring connections Physical damage to the wiring harness The following conditions may cause an intermittent malfunction: A poor connection Rubbed-through wire insulation A broken wire inside the insulation If an intermittent malfunction exists refer to General Electrical Diagnosis Procedures in Wiring Systems for further diagnosis. Test Description The numbers below refer to the step numbers on the diagnostic table.

This step checks for voltage at the EBTCM.

This step checks the Stoplamp switch.

Step Action Value(s) Yes No

SCHEMATIC REFERENCE: ABS Schematics Instrument Cluster Indicators, MSVA and Stop Lamp Switch

1 Was the Diagnostic System Check performed? -- Go to Step 2 Go to Diagnostic System Check - ABS

2 Observe the rear brake lamps.

Are the brake lamps off? -- Go to Step 4 Go to Step 3

3 Disconnect the Stoplamp Switch connector C1.

Are the brake lamps on? -- Go to Step 18 Go to Step 12

4 Press the brake pedal.

Do the brake lights come on? -- Go to Step 5 Go to Step 8

5 Turn the ignition switch to the OFF position. Disconnect the EBTCM connector C1. Install the J 39700 Universal Pinout Box using the J 39700-530 cable adapter to the EBTCM harness connector only. Using the J 39200 DMM, measure the voltage at the J 39700 terminal 6 while an assistant presses the brake pedal. Is the voltage within specifications? Battery voltage Go to Step 6 Go to Step 7

6 Replace the EBTCM. Refer to EBTCM Replacement .

Is the replacement complete? -- Go to Diagnostic System Check - ABS --

7 Repair the open or high resistance in CKT 17. Refer to Wiring Repairs in Wiring Systems.

If no open or high resistance is found, inspect both brake lamp bulbs for an open, high resistance or corrosion.

Is the circuit repair complete? -- Go to Diagnostic System Check - ABS --

8 Check the STOPLAMP fuse in the I/P Fuse Block.

Is the fuse OK? -- Go to Step 9 Go to Step 13

9 Disconnect the Stoplamp Switch connector C1. Using the J 39200 DMM, measure the voltage at the Stoplamp Switch harness connector terminal A. Is the voltage within specifications? Battery voltage Go to Step 11 Go to Step 10

10 Repair the open in CKT 140. Refer to Wiring Repairs in Wiring Systems.

Is the circuit repair complete? -- Go to Diagnostic System Check - ABS --

11 Connect a fused jumper wire between the Stoplamp Switch harness connector terminals A and B.

Do the brake lamps come on? -- Go to Step 12 Go to Step 7

12 Adjust or replace the Stoplamp Switch as necessary.

Refer to Stop Lamp Switch Adjustment or Stop Lamp Switch Replacement in Hydraulic Brakes.

Is the repair complete? -- Go to Diagnostic System Check - ABS --

13 Replace the STOPLAMP fuse. (Do not press the brake pedal.) Check the STOPLAMP fuse. Is the fuse OK? -- Go to Step 15 Go to Step 14

14 Repair the short to ground in CKT 140. Refer to Wiring Repairs in Wiring Systems.

Is the circuit repair complete? -- Go to Diagnostic System Check - ABS --

15 Press the brake pedal. Check the STOPLAMP fuse. Is the fuse OK? -- Go to Diagnostic System Check - ABS Go to Step 16

16 Turn the ignition switch to the OFF position. Disconnect the EBTCM. Replace the fuse. Depress the brake pedal. Check the STOPLAMP fuse. Is the fuse OK? -- Go to Step 6 Go to Step 17

17 Repair the short to ground in CKT 17. Refer to Wiring Repairs in Wiring Systems.

Is the circuit repair complete? -- Go to Diagnostic System Check - ABS --

18 Repair CKT 17 for a short to voltage. Refer to Wiring Repairs in Wiring Systems.

Is the repair complete? -- Go to Diagnostic System Check - ABS --

-------------------------------------------------------------------------------- Document ID# 574942

2000 Pontiac Grand Prix
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