P20C1: Reductant Heater Control Circuit/Open
The P20C1 code indicates a fault in the reductant heater control circuit, typically found in diesel vehicles with Selective Catalytic Reduction (SCR) systems. The heater is responsible for warming the diesel exhaust fluid (DEF) to prevent freezing and ensure proper injection. An open circuit means there is a break in the electrical path, preventing the heater from functioning. This can be caused by a blown fuse, damaged wiring, a faulty relay, or a failed heater element. The issue is common in colder climates and can lead to increased emissions and potential limp mode.
01. Most Common Causes
- Blown fuse or open circuit in the reductant heater wiring
- Faulty reductant heater relay
- Damaged or corroded connector at the heater
- Failed reductant heater element
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Reduced engine performance or limp mode
- Increased diesel exhaust fluid consumption
- Poor fuel economy
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 fuse and replace if blown.
Step 3: Test the heater relay and wiring for continuity and voltage.
Step 4: Check the heater element resistance with a multimeter; replace if open.
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. In some cases, the vehicle may enter limp mode.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for parts and labor, depending on whether a fuse, relay, or heater element needs replacement.