Code
C1743
HUMMER
C — Chassis
Speed Signal Fault
AI status
Completed
Completed
100%
Causes
- Open or shorted speed-sensor wiring or connector
- Faulty vehicle speed sensor (VSS) or wheel speed sensor
- Damaged reluctor (tone) ring or missing teeth
- Poor ground or power supply to sensor or control module
- Faulty ABS/ESC/BCM/PCM module or internal software error
- Intermittent CAN/data-bus or communication fault
Symptoms
- ABS, Traction Control or Stability Control warning light illuminated
- Cruise control inoperative or disabled
- Speedometer may be erratic or not working (if speed signal used by instrument cluster)
- Traction/ABS interventions may be incorrect or disabled
- Possible limp mode or transmission shifting irregularities (if PCM uses same speed input)
What to check
- Retrieve freeze frame and full scan-tool data — note when and what modules set C1743
- Check for other stored codes (P0500, P0720, C0035, etc.) that indicate related faults
- Inspect sensor connectors and wiring for damage, corrosion, or looseness
- Verify fuses and power/ground circuits for ABS/ESC and speed sensors
- Monitor vehicle speed signal(s) with a scan tool while driving or spinning wheels
- If available, use an oscilloscope to view sensor waveform at connector
Signal parameters
- Hall-effect sensors: 0–5 V digital square wave referenced to vehicle speed (duty/frequency increases with speed)
- Variable reluctor sensors: low-voltage AC sine wave; amplitude and frequency increase with speed (typically mV–V depending on speed)
- Expected no-load frequency/voltage varies by vehicle and wheel; compare left/right or known-good reference
- Good sensor ground and reference supply (often 5 V or battery depending on sensor type) required for valid signal
- Typical pulses per wheel/revolution depend on reluctor design (commonly 4–48 teeth)
Diagnostic algorithm
- Use a capable scan tool to read all ABS/traction/stability and powertrain modules. Record freeze-frame and live vehicle speed values from multiple modules (ABS, PCM, cluster).
- Confirm whether the fault is for wheel sensor(s) or vehicle speed sensor: compare speed reported by each wheel sensor and PCM. Look for mismatch or no reading.
- Visually inspect the suspect sensor(s), reluctor ring, and harness for damage, debris, missing teeth, or metal contamination.
- Check connectors for corrosion, bent pins, water ingress. Disconnect and inspect terminals; clean and apply correct dielectric where specified.
- Verify power and ground at sensor connector (with key on) using a DMM. Confirm reference voltage if sensor requires one.
- Probe the sensor signal with an oscilloscope while wheel is rotated or during a drive-by test: verify waveform shape, amplitude and frequency. For hall sensors expect square pulses; for VR expect AC sine wave.
- Perform a wiggle test on wiring/connectors while monitoring live data or oscilloscope for intermittent changes. Repair or replace any broken wiring or corroded connectors found.
- If sensor and wiring test good, check module grounds and communication lines (CAN). Verify communication integrity with a scan tool.
- If wiring and sensors pass tests, consider module fault. Consult service manual for module bench tests, reprogramming or replacement procedures.
- After repair, clear codes, perform a test drive and re-scan to ensure C1743 does not return and related systems function normally.
Likely causes
- Corroded or disconnected sensor connector at VSS or wheel sensor
- Broken wire in harness where it flexes (frame, wheel well, steering column)
- Contaminated or damaged reluctor ring on axle/hub
- Failed hall‑effect or variable reluctor sensor
- Blown fuse or poor battery/ground connection feeding the sensor/module
- Faulty ABS/ESC control module or lost CAN messages
Fault status
Status
Indicates the ABS/traction control module detected an invalid, missing or implausible vehicle speed signal. May illuminate ABS/TCS warning and disable related functions until resolved.
Repair difficulty: Medium
Diagnostic time: 0.5-2.5 hours
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Repair manuals
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138
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