Reductant Heater Control Circuit High
The P20BC 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 uses diesel exhaust fluid (DEF) to reduce NOx emissions. A high voltage reading suggests a short to power, faulty relay, or internal heater failure, potentially causing the heater to overheat or not function properly.
01. Most Common Causes
- Short to power in the reductant heater circuit
- Faulty reductant heater relay
- Defective reductant heater element
- Damaged wiring or connector
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Reduced engine performance or limp mode
- Increased diesel exhaust fluid consumption
- Failed emissions test
03. 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: Test the heater relay and circuit for shorts to power using a multimeter.
Step 4: Measure resistance of the heater element; compare to manufacturer specs.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as the SCR system may not function properly, leading to increased emissions and potential engine derate.
How much does it cost to fix?▼
Repair costs typically range from $50 to $150 for parts and labor, depending on the root cause and vehicle model.