What does it mean?
C1212 is a Chassis (ABS, traction control, steering) fault code. It indicates: Vehicle Speed Sensor .
Symptoms
- Speedometer dead, sticking or jumping around
- Cruise control will not engage, or drops out while driving
- Harsh, delayed or erratic gear shifts and a torque converter that will not lock up
- ABS, traction and stability warning lamps on
- Odometer stops counting distance
- Idle and drivability oddities on vehicles that use road speed in their idle and shift strategy
Likely causes
- Failed vehicle speed sensor or transmission output shaft speed sensor
- Open, shorted or chafed wiring between the speed sensor and the module, often where the harness crosses the transmission bell housing
- Corroded or oil-soaked connector at the sensor, or a loose terminal
- Damaged or worn drive gear or reluctor on the output shaft, giving no pulses or missing pulses
- Vehicle speed message no longer arriving on the data network because the sending module has dropped offline
- Poor ground or missing reference voltage at the sensor
- Metal debris from transmission wear clinging to the sensor tip
How to fix it
- Compare scan tool vehicle speed with the individual wheel speeds and an independent reference while driving
- Inspect the sensor connector for oil, corrosion or spread terminals and confirm it is fully latched
- Measure sensor resistance and, where fitted, the supply and reference voltages with the key on
- Back-probe the signal wire and watch for a clean pulse train while a wheel or the output shaft is turned
- Check continuity and insulation of the signal wire from sensor to module, and check the ground path
- Remove the sensor and inspect its tip and the drive gear or reluctor for wear, debris or broken teeth
- Verify the speed message is present on the network before condemning the receiving module, then replace the sensor if the wiring tests good