Reductant Heater Control Circuit/Open
The P20C5 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 lead to failed emissions tests, reduced engine performance, and potential damage to the SCR system if not addressed.
01. Most Common Causes
- Open or shorted wiring in the reductant heater circuit
- Faulty reductant heater element
- Blown fuse or relay for the heater circuit
- Corroded or loose electrical connectors
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Reduced engine power or limp mode
- Increased diesel exhaust fluid consumption
- Failed emissions test due to high NOx levels
03. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm the code and check for related codes.
Step 2: Visually inspect the reductant heater wiring and connectors for damage, corrosion, or loose connections.
Step 3: Test the heater circuit for continuity using a multimeter; check for open or short circuits.
Step 4: Check the fuse and relay for the reductant heater; replace if blown.
Step 5: If wiring and fuses are intact, test the heater element resistance; replace if out of spec.
04. Commonly Affected Makes
05. 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. In some cases, the vehicle may enter limp mode.
How much does it cost to fix?▼
The cost to fix P20C5 typically ranges from $50 to $150 for parts and labor, depending on the cause. Replacing a heater element or repairing wiring is usually affordable, but if the entire DEF tank assembly needs replacement, costs can be higher.