Traction Control Input Signal High
The P0859 code indicates that the Powertrain Control Module (PCM) has detected a high voltage signal from the traction control system input circuit. This typically occurs when the signal voltage exceeds the normal operating range, often due to a short to voltage, faulty sensor, or wiring issue. The traction control system relies on wheel speed sensors and other inputs to modulate engine power and braking to prevent wheel slip. A high signal can cause the system to malfunction, potentially disabling traction control or causing unintended activation.
01. Most Common Causes
- Faulty traction control switch or sensor
- Short to voltage in the signal circuit
- Damaged wiring or connector
- Corroded or loose electrical connections
- Faulty PCM (rare)
02. Symptoms You Will Notice
- Traction control warning light illuminated
- Check Engine Light on
- Traction control system inoperative or erratic
- Reduced engine power or limp mode
- ABS or stability control issues
03. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm the code and check for additional codes.
Step 2: Visually inspect the traction control switch, wiring, and connectors for damage, corrosion, or loose connections.
Step 3: Test the signal circuit voltage with a multimeter; compare to manufacturer specifications.
Step 4: Check for shorts to voltage or ground in the wiring harness.
Step 5: If no issues found, test the traction control switch/sensor and replace if faulty.
Step 6: Clear the code and test drive to verify repair.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is generally safe to drive, but the traction control system may not function properly, increasing the risk of wheel slip in low-traction conditions. It's recommended to diagnose and repair promptly.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for diagnosis and repair, depending on the cause. Replacing a switch or sensor may cost $20-$100, plus labor.