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 warm the DEF in cold temperatures, potentially causing the SCR system to malfunction and increasing emissions.
01. Most Common Causes
- Open or shorted wiring in the reductant heater circuit
- Faulty reductant heater relay
- Blown fuse for the reductant heater
- Defective reductant heater element
- Corroded or loose electrical connectors
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Reduced engine performance or limp mode
- Increased diesel exhaust fluid consumption
- Failed emissions test
- Possible DEF system warnings on dashboard
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 reductant heater relay and fuse with a multimeter.
Step 4: Measure resistance across the heater element; compare to manufacturer specifications.
Step 5: If all else is fine, replace the reductant heater assembly.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is generally safe to drive short distances, but the SCR system may not function properly, leading to increased emissions and potential engine derate. It's best to address the issue promptly.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for parts and labor, depending on the specific cause and vehicle model.