P0858 Code: Traction Control Input Signal Low

What the P0858 code means

The traction control system (or the ABS) sends the transmission computer a signal when it is working, so the transmission can avoid shifting while the wheels are slipping.

It is a simple switch-type signal, so the computer sees either a high or a low voltage. The P0858 code is set when that signal sits below its minimum. A low signal usually comes from a signal wire shorted to ground or from a missing reference voltage.

When the signal fails, the transmission may shift at bad moments during wheel slip. Also check for ABS and traction control codes.

To confirm the diagnosis, unplug the component with the key on and watch what happens to the scan tool reading or to the code. If the value jumps to the opposite extreme, the wiring is fine and the component is the part pulling the signal to ground. If nothing changes, look for the short in the wire, starting where the harness rubs against the engine, the chassis or the exhaust.

P0858 code symptoms

• Check engine light on.
• Shifts during wheel slip.

Likely causes of the P0858 code

1. Signal wire shorted to ground where the harness rubs against the engine, the chassis or a bracket.
2. Reference supply shorted. If several sensors fail at once, suspect the shared reference.
3. Damaged sensor with an internal short.
4. Connector with water or corrosion, which creates a path to ground.

How to diagnose the P0858 code step by step

1. Read the sensor value on the scan tool and compare it with what you expect.
2. Inspect the connector for corrosion, water or loose pins.
3. Check power and ground with the key on: the reference should be correct and the ground voltage drop should be under 0.1 V.
4. Measure the signal with the connector plugged in and see whether it changes with the condition.
5. Do a wiggle test on the harness with the scan tool in graph mode.
6. Check continuity of each wire to the computer (under 1 ohm).
7. Check for ABS and traction control codes.

How to fix the P0858 code

• Repair the connector or the wiring.
• Replace the sensor if the tests confirm it is bad.
• Correct the real condition if there is one.
• Clear the codes and verify with a road test.

Technical reference data

• The switch or sensor is powered from the computer. Check the values in the service manual.
• Reference values are only a guide, so look up the manufacturer data for your vehicle.
• Wire continuity should be under 1 ohm, and ground voltage drop under 0.1 V.

Brand-specific notes

The letter assignment and the location of the component change from one manufacturer to another, so check the manual for your vehicle before you start testing.

The traction control signal usually starts at the ABS module, so a P0858 code that shows up alongside ABS or traction control codes often points to the module side and not to the transmission.

Frequently asked questions about P0858