Circuit Description
The electronic brake control module (EBCM) controls the operation of the brake warning lamp by means of a lamp driver module (LDM) contained within the cluster.
Battery voltage is supplied to the instrument panel (I/P) cluster terminal B14, and EBCM terminal 4 when the ignition switch is turned ON. EBCM terminals 9 and 25 are hot at all times.
The default state is for the LDM to turn ON the brake warning lamp by supplying a ground path through the LDM.
When the EBCM commands the brake warning lamp OFF, the EBCM will ground the ABS warning lamp control circuit. This causes the LDM to open the path to ground for the bulb.
When the ignition switch is turned to the ON position, the EBCM turns ON the brake warning lamp for 3 seconds for a bulb check.
Whenever a malfunction is detected within the general brake system or Mando MGH25 system, the EBCM may turn ON the brake warning lamp, notifying the driver that either brake system or MGH25 needs to be serviced.
Diagnostic Aids
Typical causes of the brake warning lamp ON with no DTCs set:
| • | Faulty emergency brake switches |
| • | Low brake fluid level or faulty brake fluid switch |
| • | DTC C0054, C0055, C0065, or C0067 fault conditions exist |
| • | De-coupled dynamic rear proportioning (DDRP) is disabled due to the following fault conditions in MGH25 ABS system: |
| - | two wheel speed sensors inoperative on the same axle |
| - | Battery 2, motor input, is short to ground |
| - | Battery 1, EBCM input, is open or short to ground |
| - | Motor ground open or short to battery |
| - | EBCM ground open or short to battery |
| - | Ignition open or short to ground |
| • | Grounded circuit between the cluster and the EBCM |
| • | Faulty cluster/LDM |
| • | Faulty EBCM |
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Diagnostic Starting Point - Vehicle? | -- | Go to Step 2 | |
2 | Observe the antilock brake system (ABS) warning lamp. Is the ABS warning lamp ON? | -- | Go to Step 4 | Go to Step 3 |
3 |
Did you find and correct the condition? | -- | System OK | -- |
4 | Connect the scan tool and retrieve the DTCs. Did the DTC exist? | -- | Go to Step 5 | |
5 |
Did the brake warning lamp turn OFF? | -- | Go to Step 6 | Go to Step 7 |
6 | Replace the EBCM. Did you complete the replacement? | -- | System OK | -- |
7 |
Does the resistance measure within the specified range? | OL (Open Circuit) | Go to Step 9 | Go to Step 8 |
8 | Find and repair the short to ground between the cluster harness and the LDM harness. Did you find and correct the condition? | -- | System OK | -- |
9 |
Does the resistance measure less than the specified value? | 2 ohms | Go to Step 11 | Go to Step 10 |
10 | Repair the open or high resistance between the LDM and the EBCM. Did you complete the repair? | -- | System OK | -- |
11 | Replace the LDM. Did you complete the replacement? | -- | System OK | Go to Step 12 |
12 | Replace the cluster assembly. Refer to Instrument Cluster Replacement . Did you complete the replacement? | -- | System OK | -- |
