Reductant Heater Control Circuit Open
The P20BD 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 the heater cannot operate, potentially causing DEF to freeze in cold weather and leading to increased emissions or limp mode.
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
- Check Engine Light illuminated
- Reduced engine power or limp mode
- Increased diesel exhaust fluid consumption
- Poor fuel economy
3. 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 connectors for damage or corrosion.
Step 3: Test the heater relay and fuse with a multimeter.
Step 4: Measure resistance across the heater element; compare to specifications.
Step 5: Check for voltage at the heater connector with the ignition on.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances, as the DEF system may not function properly, leading to increased emissions and potential limp mode. In cold weather, the DEF can freeze and cause damage.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for parts and labor, depending on whether it's a simple fuse replacement or a heater element repair.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.