X DTC C1254, C1256

anti-lock anti-lockNOTE: Refer to the PINPOINT TEST section of the Flow of Diagnosis before beginning this pinpoint test. Flow of Diagnosis

NORMAL OPERATION:
The anti-lock brake control module conducts a valve function test every time the vehicle is keyed "ON", and the wheels exceed 6.4 km/h (4 mph) for the first time. If valve function is verified, the anti-lock control system is enabled. During normal driving, B+ is applied to all of the valve solenoid coils by the anti-lock relay whenever valve activity may be required. A passive check for open or shorted valve solenoids is conducted at this time.

FAULT DESCRIPTION:
Diagnostic trouble code (DTC) C1254 (open RR isolation [ISO] valve solenoid) is generated when the anti-lock brake control module detects low ISO valve solenoid feedback voltage when it is expected to be high (B+). DTC C1256 (shorted RR ISO valve solenoid) is generated when the anti-lock brake control module detects high (B+) ISO valve solenoid feedback voltage when the solenoid is supposed to be energized.

POSSIBLE CONTRIBUTING CONDITIONS:
- Open/shorted RR ISO valve solenoid.
- Open/shorted RR ISO valve solenoid circuit 922 (P/W) between the hydraulic anti-lock actuator and the anti-lock brake control module.
- Defective circuit within the anti-lock brake control module.
- Circuit 922 (P/W) shorted to power.

X1- Check Fault Repeatability
- Turn ignition switch to "OFF".
- Connect scan tool to Data Link Connector (DLC).
- Turn ignition switch to "RUN".
- Clear all DTC's using the scan tool.
- Perform the Drive Cycle Test. Refer To Inspection and Verification.
- Retrieve DTC's from ABS memory using the scan tool.
- Is DTC C1254 or C1256 retrieved?
YES - DTC 1254 go to X2.
- DTC 1256 go to X5.
- If a different DTC is retrieved, return to DTC Index.
NO - If System Pass is obtained, go to X7.

X2- Check RR ISO Valve Solenoid Resistance
- Disconnect connector C386 from anti-lock control module and connect breakout box and adapter.
- Measure the resistance between breakout box pin 25 and pin 30.
- Is the resistance between 3 and 6 ohms?
YES - Go to X5.
NO - Go to X3.

X3- Isolate Resistance Fault
- Disconnect 12-pin connector from Hydraulic anti-lock actuator.

ABS HCU Circuit Test. RR ISO Valve:

- Measure the resistance between each of the following terminals on the hydraulic anti-lock actuator and pin 7.
- 3, 4, 5
- 12
- Were all resistances between 3 and 6 ohms?
YES - Go to X4.
NO - Replace the hydraulic anti-lock actuator and go to X7.

X4- Check Circuit Between ABS Control Module and Hydraulic Actuator

ABS HCU Circuit Test. Circuit 922:

- Measure the resistance between breakout box pin 30 and hydraulic anti-lock actuator 12-pin connector pin 7, circuit 922 (P/W).
- Measure the resistance between breakout box pin 30 and pin 1.
- Is the resistance less than 5 ohms between breakout box pin 30 and the HCU pin 7 and greater that 10,000 ohms between breakout box pin 30 and pin 1?
YES - Replace the anti-lock brake control module and go to X7.
NO - Repair circuit 922 (P/W) and go to X7.

X5- Check for RR ISO Valve Solenoid Short to Ground
- Disconnect anti-lock C386 from anti-lock control module and connect breakout box and adapter.
- Measure the resistance between breakout box pin 30 and pin 1.
- Is continuity indicated?
YES - Repair circuit 922 (P/W) and go to X6.
NO - Replace the anti-lock brake control module and go to X7.

X6- Check Circuit Between ABS Control Module and Hydraulic Actuator
- Turn ignition switch to "RUN".
- Measure the voltage between breakout box pin 30 and pin 1.
- Turn ignition switch to "OFF".
- Was the voltage greater than 0 volts?
YES - Repair circuit 922 (P/W) and go to X7.
NO - Replace the anti-lock brake control module and go to X7.

X7- Verify repair
- Restore vehicle. Reconnect all components.
- Clear all DTC's using the scan tool.
- Repeat the Drive Cycle Test.
- Retrieve DTC's using the scan tool.
- Is System Pass obtained?
YES - Stop. Repair is complete.
NO - If original code is retrieved, repeat this Pinpoint Test.
- If a different DTC is retrieved, return to DTC Index.