Circuit Description
The electronic brake control module (EBCM) monitors vehicle speed deceleration, system activation, and stoplamp switch active times in order to calculate an estimate of the brake rotor temperatures. If the EBCM calculates that the brake rotor temperatures have exceeded the thermal cutoff point, the EBCM will temporarily suspend the traction control system (TCS) function until the brake rotors cool. This feature is used to maintain braking effectiveness if normal base braking is required. An overly heated brake system could result in brake fade.
The EBCM continues calculating the brake rotor temperatures after the ignition is turned OFF. The EBCM remains awake until the EBCM calculates that the brake rotors cooled sufficiently. The cooling period may take up to 30 minutes.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC C1238 Brake Thermal Model Exceeded
Conditions for Running the DTC
The antilock brake system (ABS) conditions and the braking conditions are normal.
Conditions for Setting the DTC
This DTC sets when the estimated brake rotor temperature of either of the drive wheels exceeds 375°C (700°F). When the estimated brake rotor temperature of either of the drive wheels exceeds 375°C (700°F) during normal braking or normal ABS operations, the DTC does not set until the next TCS activation. The brake rotor temperature can exceed 375°C (700°F) without setting the DTC if a TCS activation has not occurred. When the estimated brake rotor temperature of either of the drive wheels exceeds 375°C (700°F) during a TCS activation, the DTC sets immediately, but the EBCM does not disable TCS until the end of the TCS event.
Action Taken When the DTC Sets
| • | The EBCM disables the TCS until the DTC becomes a history DTC. |
| • | The Traction Off indicator turns ON. |
| • | The ABS remains functional. |
Conditions for Clearing the DTC
| • | The current DTC becomes history when the estimated brake rotor temperatures of both drive wheels decreases below 275°C (530°F). The EBCM also enables TCS. |
| • | The condition for the DTC is no longer present and you used the scan tool Clear DTC function. |
| • | The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles. |
Diagnostic Aids
| • | With TCS temporarily disabled, the EBCM continues calculating the brake rotor temperatures after the ignition is turned OFF. Turning ON the ignition again while TCS is temporarily disabled will not re-enable TCS. |
| • | The temperature is an estimate calculated by the EBCM. |
| • | Possible causes of this DTC are the following conditions: |
| - | The brake usage is excessive. |
| - | The TCS usage is excessive. |
| - | The stop lamp switch is misaligned or damaged. |
Test Description
The number below refers to the step number on the diagnostic table.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Antilock Brake System Schematics | |||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
2 |
Does the scan tool display that this DTC is set current? | Go to Step 4 | Go to Step 3 |
3 | Since most occurrences of this DTC are caused by excessive braking, review with the customer to verify the conditions under which the DTC set. Did vehicle operation cause this DTC to set? | Go to Diagnostic Aids | Go to Step 4 |
Does the scan tool display Normal? | Go to Step 6 | Go to Step 5 | |
5 | Inspect the alignment of the stop lamp switch. Refer to Stop Lamp Switch Replacement in Lighting Systems. Did you find and correct the condition? | Go to Step 8 | Go to Step 6 |
6 |
Does the DTC reset as a current DTC? | Go to Step 7 | System OK |
7 | Replace the EBCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | Go to Step 8 | -- |
8 |
Does the DTC reset? | Go to Step 2 | System OK |
