P0857

What it means

P0857 is the generic code for a range or performance problem with the traction control input signal. The engine control unit receives a torque request or status signal from the traction or stability control system, usually over the vehicle network or a dedicated line. It has judged that signal to be implausible, out of range or inconsistent with other data such as wheel speed, throttle position or engine torque.

Symptoms

• Traction control or stability control warning light on
• Engine management light on
• Reduced engine power or limp mode
• Traction control not intervening, or intervening when it should not
• Hesitation or uneven power delivery on slippery surfaces
• ABS light on at the same time

Possible causes

• Faulty wheel speed sensor or damaged sensor wiring giving implausible speed data to the traction control modulelikely
• Wiring or connector fault (chafing, corrosion, poor pin tension) in the signal circuit between the traction control module and the engine control unitlikely
• Network communication fault or data errors between the ABS/traction control module and the engine control unitpossible
• Throttle position or accelerator pedal signal fault causing a mismatch with the torque requestpossible
• Low battery voltage or poor earth connections upsetting module signalspossible
• Faulty ABS/traction control module or engine control unitrare
• Outdated or faulty control unit software, where the manufacturer has identified it as a known cause for the modelrare

How to diagnose

1. Read all stored and pending codes from every module, and note any wheel speed, ABS, network or throttle codes alongside P0857.
2. Review freeze frame data to see speed, load and throttle position when the code set.
3. Check battery condition and charging voltage, and inspect main earth connections.
4. Inspect wheel speed sensor wiring, connectors and tone rings for damage, dirt or corrosion.
5. Inspect the wiring and connectors between the traction control module and the engine control unit, looking for chafing, water ingress and pin damage.
6. With live data, compare all four wheel speeds against vehicle speed on a straight road test and check for dropouts.
7. Check live throttle and pedal position values for smooth, plausible readings.
8. Test the signal circuit for continuity, shorts and voltage against the manufacturer's wiring diagram, as the circuit layout depends on the model and engine.

How to fix

• Replace the faulty wheel speed sensor or repair its wiring.
• Repair or replace damaged wiring and clean or replace corroded connectors in the signal circuit.
• Correct network faults found, such as damaged data lines or poor module connections.
• Repair or replace the throttle or pedal sensor if its signal is implausible.
• Restore battery condition and repair poor earths or charging faults.
• Replace or repair the faulty control module, or update its software if a known fault applies to the model, then clear the code and confirm it does not return.

Can I keep driving?

Nearby codes

• P0856GenericTraction Control Input Signal
• P0858GenericTraction Control Input Signal Low