Traction Control Input Signal Low
What does P0858 mean?
The P0858 code means the vehicle's onboard diagnostic system has detected: Traction Control Input Signal Low. This is a moderate severity code.
Common Symptoms
- Check Engine Light illuminated
- Traction control system disabled
- TCM does not receive traction control commands
- Stability control warning light on
Probable Causes (Ranked by Likelihood)
- Short to ground in traction control signal wire to TCM Very High
- Faulty ABS/traction control module output High
- Corroded wiring connector in signal path Moderate
- TCM input circuit pulled low Low
Step-by-Step Diagnostic Procedure
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Measure voltage on the traction control signal wire at the TCM connector
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Check for short to ground in the wiring between ABS module and TCM
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Inspect connectors at both modules for corrosion
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Verify ABS module output using a bidirectional scan tool
Frequently Asked Questions
What happens if the traction control signal stays low?
The TCM will not receive traction control commands and will not reduce torque during wheel slip events. The vehicle can still be driven but with reduced stability assistance.
Is P0858 related to the ABS system?
Yes, traction control is a function of the ABS system. The ABS module sends traction control data to the TCM, so ABS faults can trigger transmission-related codes.
Can I just disconnect the traction control?
Disabling traction control is not recommended as it reduces vehicle safety. The underlying electrical fault should be repaired.