Traction Control Input Signal
The P0856 code means the vehicle's onboard diagnostic system has detected: Traction Control Input Signal. This is a moderate severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- hard
- Estimated cost
- $100 - $800 (parts and labor)
Read and clear transmission codes. Many trans codes are caused by low or burnt fluid -- check level and color before assuming the worst.
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Basic scanners only read engine codes. This reads transmission, ABS, and airbag too.
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Common Symptoms
- Check Engine Light illuminated
- Traction control warning light on
- Transmission does not reduce torque during wheel slip
- Vehicle stability control system may be disabled
Probable Causes (Ranked by Likelihood)
- Communication fault between traction control module and TCM Very High
- Faulty wheel speed sensor providing incorrect data High
- Wiring fault in traction control signal circuit to TCM Moderate
- ABS module malfunction affecting traction control data Low
Step-by-Step Diagnostic Procedure
-
Scan for additional ABS and traction control DTCs
-
Check all four wheel speed sensors for proper operation
-
Inspect wiring between the ABS/traction control module and TCM
-
Verify CAN bus communication between modules using a scan tool
Frequently Asked Questions
How does traction control relate to the transmission?
The TCM reduces engine torque or adjusts shift points when the traction control system detects wheel slip. If the traction control signal is lost, the TCM cannot perform this function.
Is it safe to drive without traction control input to the TCM?
The vehicle will still drive, but the transmission will not adjust for wheel slip. Use extra caution on wet or slippery roads.
Can a bad wheel speed sensor cause P0856?
Yes, the traction control system relies on wheel speed sensors. A faulty sensor can send incorrect data that confuses both the traction control and transmission systems.
Sources
This page is built from documented references. Verify against your own service info before repair work.
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