Circuit Description
The microprocessor contains a data storage area, keep alive memory, which can save pertinent data when the ignition is turned OFF. The keep alive memory (KAM) data is lost if battery power or module ground is removed from the module. The KAM area is an integral part of the microprocessor and cannot be serviced separately.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC C1254 Abnormal Shutdown Detected
Conditions for Running the DTC
The ABS conditions and the braking conditions are normal.
Conditions for Setting the DTC
The microprocessor calculates a checksum on those areas of memory that hold critical operation data. This is done at a regular interval and is called the periodic checksum. The microprocessor also calculates a checksum on these memory locations when ever new data is written to them. This is called the running checksum.
To check the keep alive memory (KAM), the microprocessor compares the periodic checksum to the running checksum. If they do not match, the microprocessor sets the DTC.
Action Taken When the DTC Sets
If equipped, the following actions occur:
| • | The electronic brake control module (EBCM) disables the DRP/ABS for the duration of the ignition cycle. |
| • | The ABS indicator turns ON. |
| • | The red Brake warning indicator turns ON. |
| • | The EBCM will not send serial data messages. |
Conditions for Clearing the DTC
| • | The condition for the DTC is no longer present and the DTC is cleared with a scan tool. |
| • | The electronic brake control module (EBCM) automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles. |
Diagnostic Aids
Possible causes of this DTC are the following conditions:
| • | A loss of battery ground |
| • | A disconnected battery |
| • | A running reset |
| A running reset is detected when the keep alive memory check sum is not updated properly. |
| • | A sudden drop in the system voltage to less than 5 volts |
| • | Long extended engine cranks that cause the battery voltage to drop |
| • | Poor power or ground connections |
| • | An internal EBCM malfunction |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step tests for an open in the ground circuits of the body control module.
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This step verifies the proper operation of the charging system.
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This step determines whether the DTC resets.
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 |
Did you find and correct the condition? | Go to Step 8 | Go to Step 3 | |
3 | Has the battery been disconnected recently? | Go to Step 8 | Go to Step 4 |
Test the charging system. Refer to Diagnostic System Check - Vehicle in Vehicle DTC Information. Did you find and correct the condition? | Go to Step 8 | Go to Step 5 | |
5 | Inspect for poor connections at the harness connector of the EBCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 8 | Go to Step 6 |
Does the DTC reset? | Go to Step 7 | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | |
7 | Replace the EBCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the repair? | Go to Step 8 | -- |
8 |
Does the DTC reset? | Go to Step 2 | System OK |
