What Does P0858 Mean?
The traction control input signal to the PCM/TCM is reading below the expected voltage threshold. This low signal condition indicates the communication line may be shorted to ground, a module has failed with a low output state, or there is a connector issue. The PCM may not receive traction control torque reduction requests when this fault is active.
Common Causes
30%
Short to ground in the traction control signal wiring
25%
Faulty ABS/traction control module with low signal output
20%
Corroded or water-damaged connector in the signal circuit
15%
Damaged wiring harness from road debris or underbody corrosion
10%
PCM input circuit pull-up failure
Diagnostic Steps
1
Check the traction control input signal voltage at the PCM connector with the key on — compare to the manufacturer's specified voltage range.
2
Disconnect the traction control module and recheck the signal voltage at the PCM — if it rises to reference voltage, the module or its wiring is causing the low reading.
3
Test the signal wire for a short to ground between the traction control module and the PCM using a multimeter.
4
Inspect the underbody wiring harness for damage from road debris, salt corrosion, or heat exposure near exhaust components.
5
If all wiring checks pass, the ABS/traction control module may need replacement — verify by substituting a known-good module if possible.
Estimated Repair Cost
$150 - $900
Parts + labor, varies by vehicle and location
The traction control input signal to the PCM/TCM is reading below the expected voltage threshold. This low signal condition indicates the communication line may be shorted to ground, a module has failed with a low output state, or there is a connector issue. The PCM may not receive traction control ...
The most common cause of P0858 (Traction Control Input Signal Low) is: Short to ground in the traction control signal wiring
Typical repair costs for P0858 range from $150 to $900, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Traction control is likely disabled. The vehicle remains drivable, but there is no traction intervention during wheel slip events. Use extra caution on wet or slippery roads and avoid aggressive acceleration.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0858 to identify the root cause.
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Quick Info
Category
Powertrain
System
Traction Control / Powertrain Integration
Difficulty
Type
Generic (SAE)
Recommended Tools
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