Toyota/Lexus C1237: Rear Wheel Speed Signal Loss
Diagnostic trouble code C1237 indicates that the ABS or Vehicle Stability Control (VSC) module is not receiving a speed signal from one or both rear wheels. This code is specific to Toyota and Lexus vehicles and is triggered when the ABS module detects an open or short circuit in the rear wheel speed sensor circuit, a faulty sensor, or a damaged tone ring. The system relies on sine wave or Hall effect signals to determine wheel rotation speed; without this input, ABS, VSC, and sometimes traction control (TRAC) are disabled.
1. Commonly Affected Makes
2. Most Common Causes
- Faulty or worn rear wheel speed sensor
- Open, shorted, or high-resistance wiring in the rear sensor circuit
- Damaged, dirty, or misaligned tone ring (reluctor ring)
- Corroded, loose, or bent pins in the sensor connector
- Faulty ABS/VSC module unable to process the rear sensor signal
- Tire pressure mismatch or different tire sizes on the rear axle
3. Symptoms You Will Notice
- ABS warning light illuminated
- VSC/TRAC warning lights on
- ABS, VSC, or traction control inoperative
- Possible loss of stability control during braking or cornering
4. Step-by-Step Diagnosis
Scan for codes and confirm C1237 is present; check for related codes.
Inspect rear wheel speed sensor connectors for corrosion, damage, or loose fit.
Measure sensor resistance and AC voltage output while spinning the wheel; compare to specs.
Check wiring between sensor and ABS module for opens, shorts, or high resistance.
Inspect tone ring for cracks, missing teeth, or debris; ensure proper air gap.
If all else passes, test or replace the ABS/VSC module.
5. Frequently Asked Questions
Is it safe to drive?▼
Driving is possible but not recommended because ABS, VSC, and traction control will be disabled, increasing the risk of skidding or loss of control in slippery conditions. Have the issue diagnosed promptly.
How much does it cost to fix?▼
Repair costs typically range from $150 to $600, depending on the cause. A sensor replacement is usually $100–$300, while wiring repairs or module replacement can be higher.