Traction Control Input Signal High
The P0859 code indicates that the powertrain control module (PCM) has detected a voltage signal from the traction control system that is higher than the expected range. This typically occurs when the traction control switch or its circuit sends an abnormally high voltage (e.g., 5V or more) to the PCM, often due to a short to power, a faulty switch, or a wiring issue. The PCM uses this input to manage traction control functions, and an incorrect signal can disable the system or cause warning lights.
1. Symptoms You Will Notice
- Traction control warning light illuminated
- Check Engine Light on
- Traction control system inoperative
- Possible ABS light on
- No symptoms in some cases
2. Most Common Causes
- Faulty traction control switch
- Short to power in the traction control signal circuit
- Damaged wiring or connector
- Corrosion in the switch or connector
- Faulty PCM (rare)
3. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm the code and check for other related codes.
Step 2: Visually inspect the traction control switch and its wiring for damage, corrosion, or loose connections.
Step 3: Disconnect the traction control switch and measure the signal voltage at the PCM connector; it should be near 0V with the switch disconnected. If voltage is high, there is a short to power.
Step 4: Test the traction control switch continuity; replace if faulty.
Step 5: If wiring and switch are okay, check for a short to power in the circuit and repair as needed.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
Yes, it is generally safe to drive, but the traction control system may not function, which could affect vehicle stability in slippery conditions. It is recommended to diagnose and fix the issue promptly.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150, depending on whether it's a simple switch replacement or wiring repair. Diagnostic fees may add $50-$100.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.