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 the malfunction is caused by the IPC.

2. This test checks for an open in the EBCM serial data circuit.

3. This test checks for an open in the BCM serial data circuit.

4. This test determines if the malfunction is caused by the brake fluid level sensor.

5. This test checks for an open or high resistance in the brake fluid level sensor ground circuit.

6. This test checks for an open or high resistance in the brake fluid level sensor input circuit.

7. This test determines if the malfunction is caused by the park brake switch.

8. This test checks for an open or high resistance in the park brake switch input 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 |

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 Body menu then IPC on the Scan Tool .
5. Select Special Functions then Lamp Test on the Scan Tool .
6. Use the Scan Tool in order to turn the warning indicators ON.

Did the BRAKE warning indicator turn ON?

--

Go to Step 3

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

3 |

1. Select the ABS portion of the Chassis application on the Scan Tool .
2. Select Data Display on the Scan Tool .

Is data being received from the EBCM?

--

Go to Step 4

Go to No Communication with Electronic Brake Control Module in Antilock Brakes

4 |

1. Select the BCM portion of the Body application on the Scan Tool .
2. Select Data Display on the Scan Tool .

Is data being received from the BCM?

--

Go to Step 5

Go to Diagnostic System Check - Data Link Communications in Data Link Communications

5 | Apply the parking brake. Does the BRAKE warning indicator turn ON? | -- | Go to Step 6 | Go to Step 10
6 |

1. Disconnect the brake fluid level sensor connector.
2. Connect a fused jumper wire between the brake fluid level sensor connector terminals A and B.

Does the BRAKE warning indicator turn ON?

--

Go to Step 13

Go to Step 7

7 | Use the J 39200 in order to measure the resistance between the brake fluid level sensor connector terminal A and ground. Is the resistance within the specified range? | 0-2 ohms | Go to Step 8 | Go to Step 14
8 |

1. Disconnect the EBCM connector.
2. Use the J 39200 in order to measure the resistance between the EBCM connector terminal 20 and the brake fluid level sensor connector terminal B.

Is the resistance within the specified range?

0-2 ohms

Go to Step 9

Go to Step 15

9 |

1. Inspect the following components:

• | The EBCM connector

• | The brake fluid level sensor connector

2. Inspect the components for the following conditions:

• | Poor terminal contact

• | Terminal corrosion

• | Damaged terminals

Are there signs of poor terminal contact, terminal corrosion or damaged terminals?

--

Go to Step 16

Go to Step 17

10 |

1. Disconnect the park brake switch connector
2. Connect a jumper wire between the park brake switch connector terminal A and ground.

Does the BRAKE warning indicator turn ON?

--

Go to Step 18

Go to Step 11

11 |

1. Disconnect the BCM connector C2.
2. Use the J 39200 in order to measure the resistance between the BCM connector C2 terminal A9 and the park brake switch connector terminal A.

Is the resistance within the specified range?

0-2 ohms

Go to Step 12

Go to Step 19

12 |

1. Inspect the following components:

• | The BCM connector C2

• | The BCM connector C3

• | The park brake switch connector

2. Inspect the components for the following conditions:

• | Poor terminal contact

• | Terminal corrosion

• | Damaged terminals

Are there signs of poor terminal contact, terminal corrosion or damaged terminals?

--

Go to Step 16

Go to Step 20

13 | Replace the brake fluid level sensor. Refer to Brake Fluid Level Indicator Switch Replacement . Did you complete the repair? | -- | Go to Brake Warning System Check | --
14 | Repair the open or high resistance in CKT 450. Did you complete the repair? | -- | Go to Brake Warning System Check | --
15 | Repair the open or high resistance in CKT 849. Did you complete the repair? | -- | Go to Brake Warning System Check | --
16 | Replace the terminals or the connectors that exhibit the following conditions:

• | Poor terminal contact

• | Terminal corrosion

• | Damaged terminals

Did you complete the repair?

--

Go to Brake Warning System Check

--

17 | Replace the EBCM. Refer to Electronic Brake Control Module Replacement in Antilock Brakes. Did you complete the repair? | -- | Go to Brake Warning System Check | --
18 | Replace the park brake switch. Refer to Park Brake Switch Replacement in Park Brake. Did you complete the repair? | -- | Go to Brake Warning System Check | --
19 | Repair open or high resistance in CKT 1134. Did you complete the repair? | -- | Go to Brake Warning System Check | --
20 | Replace the BCM. Refer to Body Control Module Replacement in Body Control System. Did you complete the repair? | -- | Go to Brake Warning System Check | --