For 1990-2009 cars

### Circuit Description

As the wheel is rotated, the speed sensor produces an AC voltage that increases with wheel speed. The electronic brake control module (EBCM) uses the frequency of the AC signal to calculate the wheel speed. The speed sensor is connected to the EBCM by a twisted pair of wires. Twisting reduces noise susceptibility that may cause a DTC to set.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC C1201 Left Front Wheel Speed Circuit Range Performance

### Conditions for Running the DTC

Ignition is in the ON position.

### Conditions for Setting the DTC

All of the following must be true for DTC C0025 to set:

• | DTC C1200, C1203, C1206, C1209 not current

• | Brake switch OFF

• | The left front wheel speed is accelerating or decelerating beyond reasonable limits.

### Action Taken When the DTC Sets

• | The solenoid relay opens, removing power from the pump motor and solenoids.

• | DTC C1201 is stored.

• | ABS disabled, ABS warning lamp turns ON.

### Conditions for Clearing the DTC

• | If the conditions that set the DTC C1201 are no longer present, the DTC may be cleared by using the proper scan tool.

• | The DTC that has not occurred in 100 drive cycles will be cleared from history data.

### Diagnostic Aids

Thoroughly inspect the wiring and connectors when diagnosing intermittent DTCs. This will include the following:

• | Removal of the protective conduit and inspection of wiring for damage, shorts, and contamination

• | Inspection for improperly formed and/or damaged terminals

• | Checking terminal contact retention force by using a spare male/female terminal

• | Removal of the terminals from the connectors to check for proper terminal to wire crimp

If the driver comments reflect that the ABS warning lamp is ON only during moist environmental changes, such as rain, snow, vehicle wash, the all wheel speed sensor circuitry should be thoroughly inspected for signs of water intrusion. If the DTC is not current, simulate the effects of water intrusion. Use the following procedure. Spray the suspected area with a 5 percent salt water solution. Then test drive the vehicle over various road surfaces such as bumps, turns, etc., above 24 km/h (15 mph). If the DTC sets then replace the suspected harness and/or sensor.

A careful visual inspection of the wheel speed sensor for damage such as cracks should be performed. If the DTC sets at the same speed every drive cycle, the toothed ring is most likely damaged.

Failure to perform the previous steps carefully and fully can result in misdiagnosis, unnecessary component replacement, and reoccurrence of DTC C1201.

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 | Was the DTC C1200 set as a current or history DTC? | -- | Go to DTC C1200 | Go to Step 3
3 |

1. Turn the ignition switch OFF.
2. Inspect the left front wheel speed sensor and the jumper harness for damage.
3. Perform a complete and thorough inspection of the left front wheel speed sensor for damage, such as, cracks, missing teeth, looseness.

Is any physical damage noted?

--

Go to Step 4

Go to Step 5

4 | Repair the damage to the left front wheel speed sensor, and/or jumper harness. Did you find and correct the condition? | -- | Go to Step 19 | --
5 |

1. Put the vehicle in park or neutral and set the parking brake.
2. Connect a scan tool and select the data list.
3. Monitor the wheel speed sensors.
4. Start the vehicle, and monitor the wheel speed sensors with the engine running but the vehicle not moving.
5. Lightly depress the accelerator pedal to increase the engine idle speed.

Did the DTC C1201 reset or did the left front wheel speed read above 0 km/h (0 mph) when the vehicle was in park with the engine running?

--

Go to Step 6

Go to Step 7

6 |

1. The cause of the DTC C1201 is ignition noise coupled onto the left front speed sensor circuits.
2. Inspect the routing of the left front ABS body harness and/or jumper harness for potential ignition noise sources such as spark plug wires.
3. Reroute the wiring as needed.

Did you find and correct the condition?

--

Go to Step 19

--

7 |

1. The scan tool is still connected.
2. Monitor the wheel speed sensors.
3. Test drive the vehicle up to the maximum posted speed limit, and slowly decelerate to 0. Do this several times.

Did DTC C1201 reset or did the left front wheel speed vary more than 5 km/h (3 mph) when compared to any one of the other wheels during the drive?

--

Go to Step 8

Go to Diagnostic Aids

8 |

1. Put the vehicle in park or neutral and turn the ignition switch OFF.
2. Raise and suitably support the vehicle. Refer to Lifting and Jacking the Vehicle
3. Disconnect the left front jumper harness from the left front wheel speed sensor.
4. Connect an ohmmeter to terminals 2 and 1 of the left front wheel speed sensor.
5. Resistance will vary with temperature.

Is the resistance within the specified range?

800-1600 ohms

Go to Step 10

Go to Step 9

9 | Replace the left front wheel speed sensor. Refer to Front Wheel Speed Sensor Replacement . Did you complete the replacement? | -- | Go to Step 19 | --
10 |

1. The speed sensor is still disconnected from the jumper harness.
2. Connect a voltmeter to terminal 2 and 1 of the left front speed sensor.
3. Select the AC millivolt scale.
4. Spin the left front wheel while observing the voltage on the meter.

Is the AC voltage greater than the specified value?

100 mV

Go to Step 11

Go to Step 9

11 |

1. Disconnect the EBCM harness from the EBCM.
2. Disconnect the left front jumper harness from the ABS body harness.
3. Connect an ohmmeter to the EBCM harness from the ABS body harness.
4. Connect an ohmmeter to the EBCM harness terminal 20 and then to ABS body harness terminal 2.

Is the resistance measured less than the specified value?

2 ohms

Go to Step 13

Go to Step 12

12 | Repair the source open or high resistance between terminals 20 and 2. Did you find and correct the condition? | -- | Go to Step 19 | --
13 |

1. The EBCM harness is still disconnected from the EBCM.
2. The jumper harness is still disconnected from the body harness.
3. Connect an ohmmeter to the EBCM harness terminal 19 and then to ABS body harness terminal 1.

Is the resistance measured less than the specified value?

2 ohms

Go to Step 15

Go to Step 14

14 | Repair the open or high resistance between terminals 19 and 1. Did you find and correct the condition? | -- | Go to Step 19 | --
15 |

1. The EBCM harness is still disconnected from the EBCM.
2. The jumper harness is still disconnected from the body harness.
3. Connect an ohmmeter between EBCM harness terminals 20 and 19.

Is the resistance within the specified value?

OL (open circuit)

Go to Step 17

Go to Step 16

16 | Repair the short between the 2 wires. Did you find and correct the condition? | -- | Go to Step 19 | --
17 |

1. Replace the left front jumper harness.
2. Test drive the vehicle at various speeds and road surfaces.

Did DTC C1201 reset?

--

Go to Step 18

Go to Step 19

18 | Replace the EBCM. Refer to Brake Pressure Modulator Valve Assembly Replacement . Did you complete the replacement? | -- | Go to Step 19 | --
19 |

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

Does the DTC reset?

Go to Step 2

System OK