C1221

DTC C1221: Wheel Speed Sensor Input Signal = 0






Circuit Description
As wheel is rotated, wheel speed sensor produces an AC voltage whose frequency increases with wheel speed. EBCM uses frequency of the AC signal to calculate wheel speed. Speed sensor is connected to EBCM by a "twisted pair" of wires. Twisting reduces noise susceptibility, which may cause a DTC to set.

DTC Detecting Condition
All of the following must be true for DTC to set.
- DTC C1232, C1233, C1234 or C1235 not stored as current DTC.
- ABS not active.
- Brake switch off.
- Applicable 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
- ABS relay opens, removing power from the pump motor and solenoids.
- Applicable DTC is stored.
- ABS disabled, ABS warning light turns on.

Diagnostic Aids
Thoroughly inspect wiring and connectors when diagnosing intermittent DTC(s). This will include the following.
- Removal of 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 drivers comments reflect that amber ABS warning light is on only during moist environmental changes (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 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 is set then replace suspected harness and/or sensor.
When measuring wheel speed sensor resistance, ensure 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 the DTC.

DTC Troubleshooting





Steps 1 - 8





Step 9

NOTE: "ABS Check: Type 1" must be performed first before using this flow.





Table 1 for Step 7





Table 2 for Step 8