Reductant Heater Control Circuit High
The P20C4 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. The heater prevents DEF from freezing in cold temperatures. A high voltage reading suggests a short to power, a faulty heater element, or a problem with the control module.
1. Most Common Causes
- Short to power in the heater control circuit
- Faulty reductant heater element
- Damaged wiring or connectors
- Failed PCM or SCR control module
2. Symptoms You Will Notice
- Check Engine Light illuminated
- 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 all codes and freeze frame data.
Step 2: Visually inspect the reductant heater wiring and connectors for damage, corrosion, or shorts.
Step 3: Test the heater circuit voltage and resistance with a multimeter; compare to manufacturer specifications.
Step 4: If wiring is intact, test the heater element resistance; replace if out of spec.
Step 5: Clear codes and test drive; if code returns, check PCM/SCR module for faults.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as it may cause reduced performance, limp mode, or 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 diagnosis and minor repairs like wiring fixes. Heater replacement can cost $200-$500 or more.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.