Code
C1235
HUMMER
C — Chassis
Right Rear Wheel Speed Circuit Open or Shorted
Views:
UK: 11
EN: 27
RU: 30
AI status
Completed
Completed
100%
Causes
- Open or shorted wheel speed sensor wiring (broken conductor, chafing, or pinched cable)
- Corroded, loose, or disconnected sensor connector
- Failed right rear wheel speed sensor (active or passive type)
- Damaged or missing tone ring / reluctor wheel on the wheel hub or axle
- Faulty ABS control module or poor ground
- Intermittent connection due to suspension movement or heat/corrosion
Symptoms
- ABS warning lamp illuminated
- Traction control / ESC light illuminated; features may be disabled
- Possible ABS activation irregularities during braking
- Vehicle stability control or cruise control may not function correctly
- Occasional or constant fault code; may be intermittent with suspension movement
What to check
- Read ABS codes and freeze frame data with a proper scan tool; note any related codes
- Visually inspect the right rear wheel sensor, connector, and wiring harness for damage, corrosion, or disconnection
- Backprobe the connector and check for proper reference voltage and ground (for active sensors) or measure resistance (for passive sensors)
- With vehicle safely raised and supported, spin the right rear wheel and observe live wheel speed sensor data on the scan tool
- Wiggle wiring and connectors while monitoring live data to reproduce intermittent faults
- Inspect the reluctor/tone ring for missing teeth, heavy rust, dents, or contamination
Signal parameters
- Active (Hall/linear) sensors: typically use a reference (often 5V) and ground; signal is a pulsed or variable DC waveform referenced 0–5V. Verify exact reference and signal levels in the factory manual.
- Passive (variable reluctance) sensors: produce an AC voltage whose amplitude and frequency increase with wheel speed (may be a few hundred millivolts at low speed up to several volts at higher speed).
- Typical checks: resistance across sensor terminals (factory spec required), presence of reference voltage with ignition ON (for active sensors), and signal waveform while rotating the wheel using an oscilloscope or scan tool.
- Exact voltage/amplitude/resistance specs vary by model—consult the HUMMER factory service information.
Diagnostic algorithm
- Connect a scan tool and confirm C1235; record freeze frame and any related codes (ABS, wheel speed codes on other corners).
- Visually inspect the right rear sensor, tone ring, connector, and wiring for damage, contamination, or disconnection. Repair obvious damage.
- Backprobe the sensor connector: for active sensors, verify reference voltage and ground with key ON; for passive sensors, measure sensor resistance with connector disconnected. Compare to factory specs.
- With vehicle safely lifted, spin the right rear wheel and monitor wheel speed value on the scan tool. Look for a steady, proportional signal. If no signal, proceed to wiring checks.
- Perform a wiggle test on the harness and connectors while monitoring live data to find intermittent opens/shorts. Repair/replace damaged wiring or connectors and secure harness routing away from pinch points.
- If wiring and connector are good but no/erratic signal persists, remove the sensor and inspect the reluctor ring for damage, debris, or missing teeth. Clean or replace as needed.
- If sensor resistance or output is out of specified range (or waveform is distorted), replace the sensor.
- If sensor, wiring, and tone ring check OK, verify ABS module grounds and power supplies. If doubt remains about the module, consult factory procedures for module bench testing or replacement.
- After repairs, clear codes, perform a test drive and re-scan to confirm C1235 does not return.
- Safety note: Use jack stands and wheel chocks when raising the vehicle. Avoid spinning a wheel at high speed with improperly supported vehicle.
Likely causes
- Connector corrosion or broken wire at the right rear wheel (most common)
- Failed right rear wheel speed sensor
- Damaged reluctor/tone ring or debris between sensor and ring
- Wiring chafe at control arm or near wheel spindle
Fault status
Status
C1235 — Right Rear Wheel Speed Circuit Open/Shorted. ABS/traction control may be disabled; investigate sensor, wiring, and reluctor ring for open, short, or intermittent fault.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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