Reductant Heater Control Circuit Open
The P20C5 code indicates that the powertrain control module (PCM) has detected an open circuit 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. An open circuit means there is a break in the electrical path, preventing the heater from functioning. This can lead to DEF freezing in cold temperatures, causing increased emissions and potential drivability issues.
1. Most Common Causes
- Open or shorted wiring in the reductant heater circuit
- Faulty reductant heater relay or fuse
- Defective reductant heater element
- Corroded or loose electrical connectors
2. Symptoms You Will Notice
- Illuminated check engine light
- Reduced engine performance or limp mode
- Increased diesel exhaust fluid consumption
- Possible DEF freezing in cold weather
3. Step-by-Step Diagnosis
Step 1: Use a scan tool to retrieve all stored codes and freeze frame data.
Step 2: Visually inspect the reductant heater wiring and connectors for damage, corrosion, or loose connections.
Step 3: Test the reductant heater relay and fuse with a multimeter.
Step 4: Measure resistance at the heater element; compare to manufacturer specifications.
Step 5: Check for voltage at the heater connector with the ignition on; if no voltage, trace the circuit back to the PCM.
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 increased emissions and potential damage to the SCR system. In cold climates, DEF may freeze, causing blockages. If the vehicle enters limp mode, it may be unsafe to drive at highway speeds.
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. If the heater element needs replacement, costs may be higher. DIY repair can be cheaper if you have the tools and expertise.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.