For 1990-2009 cars

### Circuit Description

As the front wheels spin, each wheel speed sensor produces a digital square wave signal. The electronic brake control module (EBCM) uses the frequency of the wheel speed sensor signal to determine wheel speed.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC C0040 RF Wheel Speed Sensor Circuit

### Conditions for Running the DTC

Both of the conditions listed below may be required to set the DTC.

• | The ignition is ON.

• | The vehicle achieves a speed greater than 40 km/h (25 mph).

### Conditions for Setting the DTC

Any of the following conditions may cause this DTC to set.

• | The EBCM detects an open or shorted wheel speed sensor for 200 milliseconds.

• | The EBCM detects a missing wheel speed sensor signal for one second. If more than one absent wheel speed sensor signal is detected, the condition must be present for 20 seconds to set DTCs.

• | The EBCM detects an erratic wheel speed sensor signal for 40 continuous or cumulative milliseconds.

### Action taken when the DTC sets

If equipped, the following actions occur.

• | The EBCM disables the Antilock Brake System (ABS).

• | The EBCM disables the TCS.

• | The EBCM disables dynamic rear proportion (DRP) if all wheel speed inputs have failed.

• | The ABS indicator turns ON.

• | The ABS fault message is displayed.

• | The traction fault message is displayed.

• | The brake warning indicator turns ON, if DRP is disabled.

• | The brakes message is displayed, if DRP is disabled.

• | An ECE 13 response occurs. Refer to ABS Description and Operation for a complete description of ECE 13.

### Conditions for Clearing the DTC

The Conditions for Setting the DTC are no longer present and you use the scan tool Clear DTCs function.

### Diagnostic Aids

Thoroughly inspect connections or circuitry that may cause an intermittent malfunction. Refer to Testing for Intermittent Conditions and Poor Connections , Connector Repairs , Testing for Electrical Intermittents and Wiring Repairs .

If the customer's concern is that the ABS indicator is on only during humid conditions, such as rain, snow, or vehicle wash, thoroughly inspect the wheel speed sensor circuits for signs of water intrusion. Use the following procedure in order to help isolate the problem area:

1. Spray the suspected area with a 5 percent salt water solution.
2. Drive the vehicle at a speed greater than 19 km/h (12 mph) for at least 30 seconds.

Repair or replace the suspect harness, if the DTC sets.

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. If the DTC sets when the vehicle is not moving, the EBCM is detecting an open or shorted wheel speed sensor or wheel speed sensor circuit.

2. The front wheel speed sensors produce a high resolution signal. Therefore, the slightest rotation of the wheel causes the signal to toggle from high to low.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Antilock Brake System Schematics Connector End-View Reference: Antilock Brake System Connector End Views
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 |

1. Use a scan tool in order to clear the DTCs.
2. Operate the vehicle within the Conditions for Setting the DTC, as specified in the supporting text.

Does the DTC set?

--

Go to Step 3

Go to Diagnostic Aids

3 |

1. Turn OFF the ignition for at least 5 seconds.
2. Turn ON the ignition.
3. Use the scan tool to display Current DTCs.

Is DTC C0040 set as a current DTC?

--

Go to Step 4

Go to Step 7

4 | Test the right front wheel speed sensor signal circuit for an open or a short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 5
5 | Test the right front wheel speed sensor supply voltage circuit for an open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 6
6 |

1. Reconnect the wheel speed sensor harness connector.
2. Disconnect the electronic brake control module (EBCM) harness connector and use a fused jumper wire to connect the right front wheel speed sensor supply voltage circuit to battery positive voltage.
3. Setup the DMM to measure current flow (mA/A).
4. Connect the positive lead of the DMM to the right front wheel speed sensor signal circuit at the EBCM harness connector.
5. Connect the negative lead of the DMM to ground.

Does the amperage measure near the specified value?

35 mA

Go to Step 10

Go to Step 8

7 |

1. Turn OFF the ignition.
2. Disconnect the EBCM harness connector.
3. Raise the vehicle so that the right front wheel is 2 cm (1 in) off of the floor. Refer to Lifting and Jacking the Vehicle .
4. At the EBCM harness connector, use a fused jumper wire to connect the right front wheel speed sensor supply voltage circuit to battery positive voltage.
5. Setup the DMM to measure current flow (mA/A).
6. Connect the positive lead of the DMM to the right front wheel speed sensor signal circuit at the EBCM harness connector.
7. Connect the negative lead of the DMM to ground.
8. Slowly rotate the right front wheel by hand while observing the DMM.

Does the amperage toggle from lower measurement to higher measurement within the specified ranges?

Low signal: 4-8 mA

High signal: 12-16 mA

Go to Step 10

Go to Step 8

8 | Inspect for poor connections at the harness connector of the right front wheel speed sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9
9 | Replace the right front wheel speed sensor. Refer to Wheel Hub/Speed Sensor Replacement . Did you complete the replacement? | -- | Go to Step 12 | --
10 | Inspect for poor connections at the harness connector of the EBCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11
11 | Replace the EBCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 12 | --
12 |

1. Reconnect all electrical components.
2. Operate the vehicle within the Conditions for Running the DTC, as specified in the supporting text.

Does the DTC reset?

--

Go to Step 3

System OK