Circuit Description
DTC 1257 identifies an ABS motor circuit that shorts to ground. The malfunction will cause one of the following conditions to occur:
| • | The ABS motor will not be controlled at the commanded current rate. |
| • | The driver circuit will allow current directly to the ground. |
Conditions for Setting the DTC
DTC C1257 can set anytime.
A malfunction exists if the EBCM detects an out of range voltage on either of the left front ABS motor circuits.
An out of range voltage on either circuit indicates one of the following conditions:
| • | A circuit shorts to ground. |
| • | An ABS brake motor shorts internally. |
Action Taken When the DTC Sets
| • | A malfunction DTC stores. |
| • | The ABS disables. |
| • | The amber ABS warning indicators turn on. |
Conditions for Clearing the DTC
| • | The condition responsible for setting the DTC no longer exists and the Scan Tool Clear DTCs function is used. |
| • | 100 drive cycles pass with no DTCs detected. |
Diagnostic Aids
Use the Scan Tool Manual Control function in order to exercise ABS motor movement of affected channel in both directions while applying light pressure on the brake pedal.
An intermittent malfunction may be indicated if erratic or jumpy brake pedal movement is detected while performing an apply or release function of the ABS monitor.
The following conditions may cause an intermittent malfunction:
| • | A poor connection |
| • | Rubbed-through wire insulation |
| • | A broken wire inside the insulation |
If the malfunction is not current, use the following procedure to pinpoint an intermittent malfunction in the motor circuitry or connections:
- Wiggle the wires of the affected channel.
- Inspect if the DTC resets.
Use the enhanced diagnostic function of the Scan Tool in order to measure the frequency of the malfunction. Refer to the Scan Tool manual or Scan Tool Diagnostics located in this section for the procedure.
Thoroughly inspect any circuitry that may be causing the 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 |
Clear the DTCs after completing the diagnosis. Test drive the vehicle for three drive cycles in order to verify that the DTC does not reset. Use the following procedure in order to complete one drive cycle:
- Start the vehicle.
- Drive the vehicle over 16 km/h (10 mph).
- Stop the vehicle.
- Turn the ignition to the OFF position.
Important: Zero the J 39200 test leads before making any resistance measurements.
Step | Action | Value(s) | Yes | No | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the Diagnostic System Check performed? | -- | ||||||||||||||
2 | Install a Scan Tool. Does DTC C1257 occur intermittently? | -- | Go to Diagnostic Aids | |||||||||||||
3 |
Is the resistance within the specified range? | OL (Infinite) | ||||||||||||||
4 | Use the J 39200 in order to measure the resistance between the 6-way ABS brake motor pack harness connector terminal E and ground. Is the resistance within the specified range? | OL (Infinite) | ||||||||||||||
5 | Use the J 39200 in order to measure the resistance between the 6-way ABS motor pack connector terminal F and the terminal E. Is the resistance measured equal within the specified range? | OL (Infinite) | ||||||||||||||
6 |
Is there damage which may result in a short to ground? | -- | ||||||||||||||
7 |
Did DTC C1257 set as a current DTC in the last three drive cycles? | -- | ||||||||||||||
8 | Replace the ABS motor pack. Refer to ABS Motor Pack Replacement . Is the repair complete? | -- | -- | |||||||||||||
9 | Repair the short to ground in CKT 1280. Is the repair complete? | -- | -- | |||||||||||||
10 | Repair the short to ground in CKT 1281. Is the repair complete? | -- | -- | |||||||||||||
11 | Replace all of the following components that are damaged:
Damage may cause a short to voltage. Is the repair complete? | -- | -- | |||||||||||||
12 | Replace the EBCM. Refer to Electronic Brake Control Module Replacement . Is the repair complete? | -- | -- | |||||||||||||
13 | Is the malfunction intermittent or not present at this time? | -- | Go to Diagnostic Aids | -- |
