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.
Conditions for Setting the DTC
All of the following must be true for C0021 to set:
| • | DTC C1200, C1203, C1206, or C1209 not current |
| • | ABS not active |
| • | Brake switch OFF |
The left front wheel speed equals 0, and all of the remaining wheel speed sensors are greater than 8 km (5 mi) for at least 2.5 seconds.
Action Taken When the DTC Sets
| • | The solenoid relay opens, removing power from the pump motor and solenoids. |
| • | DTC C1202 is stored. |
| • | ABS disabled, ABS warning lamp turns ON. |
Conditions for Clearing the DTC
| • | If the conditions that set the DTC C1202 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.
When measuring wheel speed sensor resistance, ensure that the vehicle is room temperature, since resistance will increase with temperature.
Failure to perform the previous steps carefully and fully can result in misdiagnosis, unnecessary component replacement and reoccurrence of DTC C1202.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check - ABS? | -- | Go to Step 2 | |
2 |
Is any physical damage noted? | -- | Go to Step 3 | Go to Step 4 |
3 | Repair the damage to the left front wheel speed sensor, jumper harness, and/or toothed ring. Did you find and correct the condition? | -- | System OK | -- |
4 | Was DTC C1200 set as a current or history code? | -- | Go to DTC C1200 | Go to Step 5 |
5 |
Did DTC C1202 reset or did the left front wheel speed suddenly drop to 0 prior to the vehicle coming to a complete stop? | -- | Go to Step 7 | Go to Step 6 |
6 | DTC C1202 is intermittent. Refer to Diagnostic System Check - ABS . Did you find and correct the condition? | -- | System OK | -- |
7 |
Is the AC voltage greater than the specified value? | 100 mV | Go to Step 8 | Go to Step 9 |
8 | Replace the EBCM. Refer to Brake Pressure Modulator Valve Assembly Replacement . Did you complete the replacement? | -- | System OK | -- |
9 |
Is the resistance within the specified range? | 800-1600 ohms | Go to Step 11 | Go to Step 10 |
10 | Replace the left front wheel speed sensor. Did you complete the replacement? | -- | System OK | -- |
11 |
Is the AC voltage greater than the specified value? | 100 mV | Go to Step 12 | Go to Step 10 |
12 |
Is the resistance within the specified value? | OL (open circuit) | Go to Step 14 | Go to Step 13 |
13 | Find and repair the short between the 2 circuits. Did you find and correct the condition? | -- | System OK | -- |
14 |
Is the resistance measured less than the specified value? | 2 ohms | Go to Step 16 | Go to Step 15 |
15 | Repair the open or high resistance between terminals 20 and 2. Did you find and correct the condition? | -- | System OK | -- |
16 |
Is the resistance measured less than the specified value? | 2 ohms | Go to Step 18 | Go to Step 17 |
17 | Repair the open or high resistance between terminal 19 and 1. Did you find and correct the condition? | -- | System OK | -- |
18 |
Did the DTC C1202 reset? | -- | Go to Step 8 | System OK |
