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 injects diesel exhaust fluid (DEF) into the exhaust stream to reduce NOx emissions. A high voltage reading suggests a short to power, a faulty heater element, or a problem with the PCM or wiring.
1. Most Common Causes
- Shorted or damaged wiring in the reductant heater circuit
- Faulty reductant heater element
- Corroded or loose electrical connectors
- Failed PCM or relay
2. Symptoms You Will Notice
- Illuminated check engine light
- Reduced engine performance or limp mode
- Increased diesel exhaust fluid consumption
- Failed emissions test
3. Step-by-Step Diagnosis
Step 1: Use a scan tool to retrieve the code and freeze frame data.
Step 2: Visually inspect the reductant heater wiring and connectors for damage, corrosion, or shorts.
Step 3: Measure resistance of the heater element; compare to manufacturer specs.
Step 4: Check for voltage at the heater connector with the ignition on; if voltage is high, trace the circuit for a short to power.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances with this code, as it can lead to reduced engine performance, increased emissions, and potential damage to the SCR system. Limp mode may activate, limiting vehicle speed.
How much does it cost to fix?▼
The cost to fix P20BC typically ranges from $50 to $150 for diagnosis and repair, depending on the root cause. Replacing a heater element or repairing wiring may cost more if parts are needed.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.