What does it mean?
C1729 is a Chassis (ABS, traction control, steering) fault code. It indicates: Vehicle Speed Signal is in Error .
Symptoms
- Speedometer erratic, reading zero or dropping to zero while driving
- ABS, traction and stability warning lamps on together with this code
- Cruise control unavailable or dropping out on its own
- Harsh, delayed or unpredictable gearshifts; transmission may enter limp mode
- Power steering assist weight changing incorrectly because it uses the speed input
- Odometer not counting distance
Likely causes
- Faulty wheel speed sensor or a cracked, contaminated or damaged tone/reluctor ring
- Chafed, broken or shorted wiring in the speed signal circuit, usually where it flexes with the suspension
- Transmission output speed sensor failed or its connector corroded
- The module that broadcasts vehicle speed on the network is offline or sending an implausible value
- ABS/HECU internal fault preventing the speed message from being transmitted
- Non-standard tyre size or a changed final drive ratio making the calculated speed disagree with other sources
- Failed input circuit in the receiving module or a poor ground shared by the speed circuit
How to fix it
- Scan every module and note which ones also report a lost or implausible speed signal; a network fault must be resolved first
- Compare all four wheel speed values in live data during a road test and look for one that drops out
- Compare the speed shown by the cluster with the value seen by the chassis module
- Inspect wheel speed and output speed sensor connectors and the harness for chafing near suspension pivots
- Measure sensor output or resistance and check the air gap and tone ring for damage or debris
- Check network continuity and termination resistance if a whole module is missing from the bus
- Repair the wiring or replace the failed sensor, clear the code and confirm the speed data is stable on a road test