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 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 control module.
01. Most Common Causes
- Short to power in the reductant heater circuit
- Faulty reductant heater element
- Damaged wiring or connector
- Failed PCM or SCR control module
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Reduced engine performance or limp mode
- Increased emissions
- Possible DEF system warnings
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: 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: Check for shorts to power or ground in the circuit; repair as needed.
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 it can lead to reduced engine performance, increased emissions, and potential damage to the SCR system. Limp mode may activate.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for diagnosis and repair, but can be higher if the heater element or control module needs replacement.