For 1990-2009 cars
Hydraulic Brakes Components
Brake Warning System Schematics

### Circuit Description

The BRAKE warning indicator has the following two functions:

• | The BRAKE warning indicator will light whenever the park brake is set. The body control module (BCM) will command the indicator on via serial data with the instrument cluster.

• | A switch built into the brake master cylinder reservoir will signal the electronic brake control module (EBCM) if the brake fluid level drops below a safe level. The EBCM will command the indicator on via serial data with the instrument cluster. In addition, the indicator is commanded on when the EBCM is initially powered up (the ignition switch is turned to the ON position).

### Diagnostic Aids

The following conditions will activate the brake warning indicator:

• | An applied parking brake while the ignition switch is in the ON position

• | A low fluid level in the master cylinder

Thoroughly inspect any circuitry that may cause an 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

1. This test determines if an ABS malfunction has turned the BRAKE warning indicator on.

2. This test determines if the brake level switch circuit is commanding the brake warning indicator on.

3. This test determines if the park brake circuit is commanding the BRAKE warning indicator on.

4. This test checks for a park brake switch stuck in the closed position.

5. This test checks for a short to ground in the park brake switch circuit.

6. This test checks for a brake fluid level sensor stuck in the closed position.

7. This test checks for a short to ground in the brake fluid level sensor circuit.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
Important: Zero the J 39200 test leads before making any resistance measurements. Refer to the J 39200 user's manual.
1 | Did you perform the Brake Warning System Check? | -- | Go to Step 2 | Go to Brake Warning System Check
2 | Is the amber ABS warning indicator also ON? | -- | Go to Diagnostic System Check - ABS | Go to Step 3
3 |

1. Turn the ignition switch to the OFF position.
2. Connect a Scan Tool .
3. Turn the ignition switch to the ON position.
4. Select the Chassis menu on the Scan Tool .
5. Select Data Display then ABS Data on the Scan Tool .
6. Observe the Brake Warning Lamp Cmd status.

Does the scan tool indicate that the Brake Warning Lamp Cmd is ON?

--

Go to Step 8

Go to Step 4

4 |

1. Select BCM on the Scan Tool .
2. Select Data Display then Inputs on the Scan Tool .
3. Monitor the Park Brake Switch input.

Does the Scan Tool indicate that the Park Brake Switch is ON?

--

Go to Step 5

Go to Diagnostic System Check - Instrument Cluster in Instrument Panel, Gauges and Console

5 | Is the park brake fully released? | -- | Go to Step 6 | Go to Step 10
6 |

1. Turn the ignition switch to the OFF position.
2. Disconnect the Scan Tool from the vehicle.
3. Disconnect the park brake switch connector.
4. Turn the ignition switch to the ON position.

Did the BRAKE warning indicator turn off?

--

Go to Step 11

Go to Step 7

7 |

1. Turn the ignition switch to the OFF position.
2. Disconnect the BCM connector C2.
3. Use the J 39200 in order to measure the resistance between the park brake switch connector terminal A and ground.

Is the resistance within the specified range?

OL (Infinite)

Go to Body Control Module System Check in Body Control Systems

Go to Step 12

8 |

1. Turn the ignition switch to the OFF position.
2. Disconnect the Scan Tool from the vehicle.
3. Disconnect the brake fluid level sensor connector.
4. Turn the ignition switch to the ON position.

Did the BRAKE warning indicator turn off?

--

Go to Step 13

Go to Step 9

9 |

1. Turn the ignition switch to the OFF position.
2. Disconnect the EBCM connector.
3. Use the J 39200 in order to measure the resistance between the brake fluid level sensor connector terminal B and ground.

Is the resistance within the specified range?

OL (Infinite)

Go to Step 14

Go to Step 15

10 | Release the park brake. Is the action complete? | -- | Go to Brake Warning System Check | --
11 | Replace the park brake switch. Refer to Park Brake Warning Switch Replacement in Park Brake. Did you complete the repair? | -- | Go to Brake Warning System Check | --
12 | Repair the short to ground in CKT 1134. Did you complete the repair? | -- | Go to Brake Warning System Check | --
13 | Replace the master cylinder fluid level sensor. Refer to Brake Fluid Level Indicator Switch Replacement . Did you complete the repair? | -- | Go to Brake Warning System Check | --
14 | Replace the EBCM. Refer to Electronic Brake Control Module Replacement in Antilock Brake System. Did you complete the repair? | -- | Go to Brake Warning System Check | --
15 | Repair the short to ground in CKT 849. Did you complete the repair? | -- | Go to Brake Warning System Check | --