Reductant Heater Control Circuit High
The P20C8 code indicates that the powertrain control module (PCM) has detected a high voltage condition in the reductant heater control circuit. This heater is part of the selective catalytic reduction (SCR) system, which heats diesel exhaust fluid (DEF) to prevent freezing and ensure proper injection. A high voltage reading typically points to a short to power, a faulty heater element, or a wiring issue.
1. Most Common Causes
- Short to power in the reductant heater circuit
- Faulty reductant heater element
- Damaged wiring or connector
- Failed PCM (rare)
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Reduced engine power or limp mode
- Increased diesel exhaust fluid consumption
- Poor fuel economy
3. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm the code and check for related codes.
Step 2: Visually inspect the reductant heater wiring and connector for damage or corrosion.
Step 3: Measure voltage at the heater connector with the ignition on; compare to manufacturer specs.
Step 4: Test the heater resistance with a multimeter; replace if out of range.
Step 5: If wiring and heater are okay, check for a short to power in the circuit.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as it can lead to reduced engine power and potential damage to the SCR system. Immediate diagnosis is advised.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for parts and labor, depending on the cause and vehicle model.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.