Circuit Description
As the wheel is rotated, the speed sensor produces an alternating current (AC) voltage that increases with wheel speed. The electronic brake control module (EBCM) uses the frequency of the AC signal to calculate 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 DTC C0021 to set:
| • | DTC C0032, C0033, C0034, or C0035 not current |
| • | Antilock brake system (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/h (5 mph) 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 C0021 is stored. |
| • | The ABS is disabled, ABS warning lamp turns ON. |
Conditions for Clearing the DTC
| • | If the conditions that set DTC C0021 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 |
| • | Inspecting terminal contact, retention force, by using a spare male/female terminal |
| • | Removal of the terminals from the connectors to inspect for proper terminal to wire crimp. |
If the drivers comments reflect that the ABS warning lamp is ON only during moist environmental changes such as rain, snow, vehicle wash, 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, replace the suspected harness and/or sensor.
When measuring wheel speed sensor resistance ensure the vehicle is at 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 C0021.
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 C0032 set as a current or history code? | -- | Go to DTC C0032 | Go to Step 5 |
5 |
Did DTC C0021 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 C0021 is intermittent. Refer to Diagnostic Aids. Did you find and correct the condition? | -- | System OK | -- |
7 |
Is the AC voltage within the specified range? | At least 100 mV | Go to Step 8 | Go to Step 9 |
8 | Replace the EBCM. Did you complete the replacement? | -- | System OK | -- |
9 |
Important: Resistance will vary with temperature. Does the resistance measure within the specified value? | 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 within the specified range? | At least 100 mV | Go to Step 12 | Go to Step 10 |
12 |
Does the resistance measure 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 |
Does the resistance measure less than the specified value? | 2 ohms | Go to Step 16 | Go to Step 15 |
15 | Repair the open or high resistance between terminals A9 and 2. Did you find and correct the condition? | -- | System OK | -- |
16 |
Does the resistance measure less than the specified value? | 2 ohms | Go to Step 18 | Go to Step 17 |
17 | Repair the open or high resistance between terminal A10 and 1. Did you find and correct the condition? | -- | System OK | -- |
18 |
Did DTC C0032 reset? | -- | Go to Step 8 | System OK |
