Code
C1291
HYUNDAI
C — Chassis
Torque Sensor Sub Signal-Open/Short | Torque Sensor Sub Signal Fail
Views:
UK: 15
EN: 22
RU: 39
AI status
Completed
Completed
100%
Causes
- Open or short in torque sensor sub-signal wiring (broken conductor, chafing, pinched harness)
- Poor or corroded connector at torque sensor or EPS module
- Torque sensor internal failure (secondary/output element)
- Poor ground or missing reference voltage to the sensor
- Water intrusion or contamination at connectors/steering column
- Faulty EPS control module or intermittent module internal fault
Symptoms
- EPS warning lamp or steering warning on dash
- Reduced, inconsistent or jerky power assist; heavier manual steering
- Stored trouble code(s) and possible limp/limited steering assist
- Steering torque feel differs left vs right or around center
- Other related codes (steering angle, communication) may be present
What to check
- Read and record all stored codes and freeze frame data with a scan tool
- Verify vehicle conditions that set code (key ON, engine ON, steering movement)
- Visually inspect torque sensor connector(s), wiring, and steering-column harness for damage, corrosion or loose pins
- Wiggle harness/connectors while monitoring live data to reproduce fault
- Check relevant fuses and module grounds
- Measure sensor supply/reference voltage and ground at the connector with DMM
Signal parameters
- Reference/supply voltage: typically ~5.0 V (verify factory spec)
- Signal idle (center) voltage: ~2.5 V (varies by design)
- Signal swing with torque applied: approximately ±0.2–1.0 V around center (varies by model)
- Open-circuit: signal reads very low (near 0 V) or high/erratic; short-to-ground ≈0 V; short-to-battery ≈12 V or supply voltage
- Expected steady resistance between sensor internal circuits per factory spec — check service manual for exact ohms
Diagnostic algorithm
- Connect a factory-level scan tool. Record C1291 and any related codes; clear codes and attempt to reproduce (steering at key ON/engine running as required).
- Visually inspect torque sensor connectors, wiring, and steering column harness for damage, corrosion, pin deformation or signs of water ingress. Repair any obvious damage.
- With ignition ON (engine off unless manufacturer specifies otherwise), measure reference voltage and ground at the torque sensor connector. Reference should be present and stable (usually ~5 V). If reference missing, trace to fuse/power source and EPS module.
- Measure sub-signal voltage at the sensor connector at rest (centered steering). Expect center voltage ~2.5 V (consult service manual). Move steering and observe voltage change; if no change or erratic, suspect sensor or wiring.
- Check continuity between sensor signal pin(s) and EPS control module connector; check for short to battery and short to ground. Repair any open or shorted circuits.
- If wiring and connector checks good but signal out of range or erratic, replace torque sensor (or sensor assembly) and re-test. Some systems use a removable sensor; follow service manual for replacement and calibration.
- If new sensor still produces C1291, suspect EPS control module or module input circuit. Verify module power/grounds and CAN/communication lines. Replace module only after all wiring and sensor tests are confirmed.
- After repair, clear codes, perform any required steering/torque sensor calibration or ECU adaptations, and road test to confirm proper operation.
- Safety note: Secure vehicle and follow steering column airbag and SRS safety procedures when working near steering column and clockspring.
Likely causes
- Wiring harness abrasion near steering column or bellows
- Bent or pushed-out connector pins at sensor or module
- Sensor internal electronics failed (age, impact, moisture)
- Connector corrosion allowing intermittent open/short
- Loss of sensor reference 5V or ground due to blown fuse or poor chassis ground
Fault status
Status
Torque sensor sub-signal open/short detected. EPS control module has logged a torque sensor sub-signal failure — steering assist may be reduced or intermittent until fault is repaired.
Repair difficulty: Medium
Diagnostic time: 1.0-2.5 hours
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