GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 Safari - 4WD 🢒 Brakes 🢒 Antilock Brake System 🢒 DTC C0281 or C081 Brake Switch Circuit

Object Number: 191400 Size: MF
ABS Components
Antilock Brake System Schematics

Circuit Description

The Stop Lamp Switch is normally closed. With the ignition in the RUN position and the brake pedal not depressed, the EBCM will have ignition voltage present at terminal C of the 10-way connector. When the brakes are applied, the ignition voltage present at the EBCM will be zero.

Conditions for Setting the DTC
    • After power-up, the microprocessor never sees the brake switch released and the vehicle reaches a speed above 24 km/h (15 mph), or
    • The vehicle is in an ABS stop for more than 2 seconds and the brake switch is not depressed

Action Taken When the DTC Sets
    • The ABS indicator lamp will not be illuminated
    • The ABS will not be disabled

DTC C0281 is advisory code only. The DTC is stored in memory, but the ABS indicator lamp will not light, and ABS will not be disabled.

Conditions for Clearing the DTC
    • Repair the conditions responsible for setting the DTC
    • Use the Scan Tool

Diagnostic Aids

DTC C0281 can be set by a faulty Stop Lamp Switch, misadjusted Stop Lamp Switch or damage in CKT 420 or CKT 441.

Thoroughly check any circuitry that is suspected of causing the intermittent 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

Test Description

The numbers below refer to the steps in the diagnostic table:

  1. This step checks the functionality of the Stop Lamp Switch circuit using the Scan Tool.

    2.

  2. This step checks for a short to voltage in the Stop Lamp Switch circuit between the Stoplamp Switch and the EBCM.

    3.

  3. This step checks the functionality of the Stop Lamp Switch circuit using the Scan Tool.

    4.

  4. This step checks for an open in the Stop Lamp Switch circuit between the Stoplamp Switch and the EBCM.

Step

Action

Value(s)

Yes

No

1

Was the Diagnostic System Check performed?

--

Go to Step 2

Go to Diagnostic System Check

2

  1. Install the Scan Tool .
  2. Turn the ignition to RUN.
  3. Using the Data List function of the scan tool, check the operation of the Stop Lamp Switch while applying and releasing the brake pedal.

Does the scan tool indicate that the Stop Lamp Switch is closed (when pedal is not applied)?

--

Go to Step 3

Go to Step 4

3

  1. Turn the ignition to OFF.
  2. Disconnect the Stoplamp Switch harness connector from the Stoplamp Switch.
  3. Turn the ignition to RUN
  4. Using the Data List function of the scan tool, check the operation of the Stop Lamp Switch.

Does the scan tool indicate that the Stop Lamp Switch is closed?

--

Go to Step 10

Go to Step 8

4

Does the scan tool indicate that the Stop Lamp Switch is open constantly (pedal applied)?

--

Go to Step 5

Go to Step 7

5

  1. Turn the ignition to OFF.
  2. Disconnect the 10-way EBCM connector from the EBCM.
  3. Turn the ignition to RUN.
  4. Using a J 39200 , measure the voltage between terminal C of the 10-way EBCM harness connector and ground.

Is the voltage within the specified range?

10-15V

Go to Step 6

Go to Step 11

6
  1. Turn the ignition to OFF.
  2. Reconnect all connectors.
  3. Turn the ignition to RUN.
  4. Install the Scan Tool ,
  5. Using the Data List function of the scan tool, check the operation of the Stop Lamp Switch .

Does the scan tool indicate that the Stop Lamp Switch is open constantly while applying and releasing the brake pedal?

--

Go to Step 9

Go to Step 7

7

Malfunction is intermittent.

  1. Refer to diagnostic aids.
  2. Repair all damage found.

Is repair compete?

--

Go to Diagnostic System Check

--

8
  1. Check for misadjusted Stop Lamp Switch.
  2. If the Stoplamp Switch is adjusted properly, replace the Stoplamp Switch.

Is repair complete?

--

Go to Diagnostic System Check

--

9

Replace the EBCM.

Refer to Electronic Brake Control Module Replacement .

Is the repair complete?

--

Go to Diagnostic System Check

--

10

Repair the short to voltage in CKT 420.

Is the repair complete?

--

Go to Diagnostic System Check

--

11

Check for the following:

    • Misadjusted Stop Lamp Switch
    • Faulty Stoplamp switch
    • Open circuit between Stoplamp switch and EBCM

Is repair complete?

--

Go to Diagnostic System Check

--