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Pinpoint Test P: Unintended ABS Activation, ABS Too Sensitive, ABS Activates On a Normal Stop




Anti-Lock Control

Pinpoint Test P: Unintended ABS Activation, ABS Too Sensitive, ABS Activates on a Normal Stop

Refer to Wiring Diagram Set 42, Vehicle Dynamic Systems for schematic and connector information Electrical Diagrams.

Normal Operation

The wheel speed sensor and sensor tone ring generate a signal to the ABS module that is proportional to wheel speed. The ABS module compares the wheel speed inputs from all wheel speed sensors to determine an impending wheel lockup.





This pinpoint test is intended to diagnose the following:

- Front/rear suspension concern

- Parking brake shoes out of adjustment (dragging)

- Wheel speed sensor ring

- Wheel speed sensor

- ABS module

- Wiring, terminals or connectors

PINPOINT TEST P : UNINTENDED ABS ACTIVATION, ABS TOO SENSITIVE, ABS ACTIVATES ON A NORMAL STOP

NOTICE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.

NOTE: Anytime a wheel speed sensor is removed, thoroughly clean the mounting surfaces and apply a thin coating of grease.

P1 CHECK THE SUSPENSION

- Inspect the front and rear suspension for signs of wear or damage.

Are any suspension concerns found?

Yes
REFER to Front Suspension &/or Steering Knuckle or Rear Suspension to repair the concern. TEST the system for normal operation after the repair.

No
GO to P2.

P2 CHECK THE PARKING BRAKE ADJUSTMENT

- Disengage the parking brake.

- Inspect the parking brake shoes for correct adjustment.

Are any parking brake concerns found?

Yes
REFER to Parking Brake System to repair the concern. TEST the system for normal operation after the repair.

No
GO to P3.

P3 CHECK THE ABS MODULE DTCs

- Review the ABS module DTCs retrieved and recorded during Inspection and Verification.

Is DTC C1145, C1155, C1165 or C1175 also present?

Yes
GO to Pinpoint Test D. Pinpoint Test D: DTCs C1145, C1155, C1165 and C1175

No
GO to P4.

P4 MONITOR THE WHEEL SPEED SENSOR PIDs

- Connect the scan tool.

- Ignition ON.

- Enter the following diagnostic mode on the scan tool: DataLogger- ABS Module.

- While driving the vehicle at the speed at which the concern occurred, monitor the following PIDs:
- Left Front Wheel Speed Sensor (LF_WSPD)

- Right Front Wheel Speed Sensor (RF_WSPD)

- Left Rear Wheel Speed Sensor (LR_WSPD)

- Right Rear Wheel Speed Sensor (RR_WSPD)


Are the wheel speed PIDs consistent with the vehicle speed and each other?

Yes
CLEAR the DTCs. DRIVE the vehicle. REPEAT the self-test. RETRIEVE and RECORD any ABS module DTCs.

If DTC C1233, C1234, C1235 or C1236 returns, GO to P10.

For all other ABS module DTCs, REFER to the ABS Module DTC Chart. Antilock Brakes / Traction Control Systems

If no DTCs return, INSPECT the ABS module and wheel speed sensor connectors for corrosion, pushed-out pins, or spread terminals and REPAIR as necessary. The concern may have been caused by a loose or corroded connector.

No
If the Rotunda Active Wheel Speed Sensor Tester is available, GO to P5.

If the Rotunda Active Wheel Speed Sensor Tester is not available, GO to P7.

P5 CHECK THE ABS MODULE OUTPUT USING THE ROTUNDA ACTIVE WHEEL SPEED SENSOR TESTER

- Ignition OFF.

- Disconnect: Suspect Wheel Speed Sensor.

- Connect the Active Wheel Speed Sensor Tester to the wheel speed sensor connectors.

- Select the correct system polarity on the Active Wheel Speed Sensor Tester and turn the power switch to the ON position.

- Ignition ON.

Is the module output LED illuminated?

Yes
GO to P6.

No
GO to P8.

P6 CHECK THE WHEEL SPEED SENSOR OUTPUT WITH THE ROTUNDA ACTIVE WHEEL SPEED SENSOR TESTER

- Raise the suspect wheel until it can spin freely.

- While monitoring the Active Wheel Speed Sensor Tester, slowly spin the suspect wheel.

Do the sensor output LEDs illuminate and flash and is the current overload LED not illuminated?

Yes
INSPECT the wheel speed sensor tone ring for damage and looseness. INSTALL new components as necessary. If the tone ring is OK, the concern may have been caused by a loose or corroded connector. CLEAR the DTCs. REPEAT the self-test.

No
If the current level LED is not illuminated and the sensor output LEDs do not illuminate or if the current level LED is illuminated red, INSTALL a new wheel speed sensor. REFER to Wheel Speed Sensor - Front or Wheel Speed Sensor - Rear . CLEAR the DTCs. REPEAT the self-test.

If the current level LED is not illuminated and the sensor output LEDs illuminate green but do not flash, INSPECT the wheel speed sensor tone ring and INSTALL new if necessary. If the tone ring is OK, INSTALL a new wheel speed sensor. REFER to Wheel Speed Sensor - Front or Wheel Speed Sensor - Rear . CLEAR the DTCs. REPEAT the self-test.

P7 CHECK THE ABS MODULE OUTPUT

NOTE: If the 2 wheel speed sensor circuits are shorted together, the ABS module shuts down those circuits and no voltage is present at the connectors. If this happens, cycle the ignition key and take the measurement again, being careful not to short the 2 wheel speed sensor circuits together.

- Disconnect: Suspect Wheel Speed Sensor.

- Ignition ON.

- For DTC C1234, measure the voltage between RF wheel speed sensor C160-1, circuit VCA05 (GY/VT), harness side and RF wheel speed sensor C160-2, circuit RCA19 (VT), harness side.

- For DTC C1233, measure the voltage between LF wheel speed sensor C150-1, circuit VCA03 (VT/WH), harness side and LF wheel speed sensor C150-2, circuit RCA17 (YE), harness side.

- For DTC C1235, measure the voltage between RR wheel speed sensor C426-1, circuit VCA06 (WH/OG), harness side and RR wheel speed sensor C426-2, circuit RCA20 (BN), harness side.

- For DTC C1236, measure the voltage between LR wheel speed sensor C440-1, circuit VCA04 (BU/OG), harness side and LR wheel speed sensor C440-2, circuit RCA18 (BN/GN), harness side.





Is the voltage greater than 10 volts?

Yes
GO to P9.

No
GO to P8.

P8 CHECK THE WHEEL SPEED SENSOR CIRCUITS FOR AN OPEN

NOTE: Both circuits must be checked for each DTC.

- Ignition OFF.

- Disconnect: ABS Module C135.

- Disconnect: Suspect Wheel Speed Sensor.

- Measure the resistance between the ABS module connector, harness side and the suspect wheel speed sensor connector, harness side as follows:

DTC ABS Module Circuit Wheel Speed Sensor C1145 C135-33 RCA19 (VT) C160-2 C135-34 VCA05 (GY/VT) C160-1 C1155 C135-46 RCA17 (YE) C150-2 C135-45 VCA03 (VT/WH) C150-1 C1165 C135-42 RCA20 (BN) C426-2 C135-43 VCA06 (WH/OG) C426-1 C1175 C135-37 RCA18 (BN/GN) C440-2 C135-36 VCA04 (BU/OG) C440-1






Are the resistances less than 5 ohms?

Yes
GO to P12.

No
REPAIR the affected circuit(s). CLEAR the DTCs. REPEAT the self-test.

P9 CHECK THE WHEEL SPEED SENSOR AND MOUNTING

- With the gear selector in NEUTRAL, position the vehicle on a hoist.

- Inspect the wheel speed sensor for looseness.

Is the wheel speed sensor and mounting OK?

Yes
GO to P11.

No
TIGHTEN the wheel speed sensor to specification, REFER to Specifications. CLEAR the DTCs. GO to P10.

P10 RECHECK THE WHEEL SPEED SENSOR PIDs

- While driving the vehicle at a constant speed, monitor the following PIDs:
- Left Front Wheel Speed Sensor (LF_WSPD)

- Right Front Wheel Speed Sensor (RF_WSPD)

- Left Rear Wheel Speed Sensor (LR_WSPD)

- Right Rear Wheel Speed Sensor (RR_WSPD)


Are all the wheel speed sensor PIDs consistent with the vehicle speed and each other?

Yes
The system is operating correctly at this time. The concern may have been caused by a loose wheel speed sensor.

No
GO to P11.

P11 CHECK THE WHEEL SPEED SENSOR(S) FOR DAMAGE

- Ignition OFF.

- With the gear selector in NEUTRAL, position the vehicle on a hoist.

- Remove the wheel speed sensor. Refer to Wheel Speed Sensor- Front or Wheel Speed Sensor- Rear .

- NOTE: Examine the wheel speed sensor wire carefully, using a good light source. Failure to verify damage in the wheel speed sensor wire can lead to unnecessary installation of a new component.

Inspect the wheel speed sensor and attached wire harness for general damage.


Is the wheel speed sensor and harness OK?

Yes
INSTALL a new wheel hub and bearing (wheel speed sensor tone rings are part of the wheel hub and bearing assembly). CLEAR the DTCs. REPEAT the self-test.

No
INSTALL a new wheel speed sensor. REFER to Wheel Speed Sensor - Front or Wheel Speed Sensor - Rear . CLEAR the DTC. REPEAT the self-test.

P12 CHECK FOR CORRECT ABS MODULE OPERATION

- Ignition OFF.

- Disconnect: ABS Module C135.

- Check ABS module C135 for:
- corrosion

- pushed-out pins

- spread terminals


- Connect: ABS Module C135.

- Connect: Suspect Wheel Speed Sensor.

- Make sure the connector seats correctly, then operate the system and verify the concern is still present.

Is the concern still present?

Yes
INSPECT the wheel speed sensor tone ring for damage. INSTALL new components as necessary. If the tone ring is OK, INSTALL a new ABS module. REFER to Anti-Lock Brake System (ABS) Module . TEST the system for normal operation.

No
The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. CLEAR the DTCs. REPEAT the self-test.

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