Reductant Heater Control Circuit Low
The P20BF code indicates that the powertrain control module (PCM) has detected a low voltage condition in the reductant heater control circuit. This heater is part of the selective catalytic reduction (SCR) system, which injects diesel exhaust fluid (DEF) into the exhaust stream to reduce NOx emissions. The heater prevents DEF from freezing in cold temperatures. A low circuit condition typically means the voltage is below the expected threshold, often due to a short to ground, open circuit, or faulty heater element.
01. Most Common Causes
- Faulty reductant heater element
- Open or shorted wiring in the heater control circuit
- Corroded or loose connector at the heater
- Failed PCM (rare)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Reduced engine performance or limp mode
- Increased diesel exhaust fluid consumption
- Possible DEF system warning messages on dashboard
03. Step-by-Step Diagnosis
Step 1: Scan for additional codes and freeze frame data.
Step 2: Visually inspect the reductant heater connector and wiring for damage, corrosion, or loose connections.
Step 3: Measure resistance of the heater element; compare to manufacturer specifications (typically 0.5-5 ohms).
Step 4: Check for voltage at the heater connector with the ignition on; should be battery voltage (12V).
Step 5: If voltage is low or absent, test the control circuit from PCM to heater for opens or shorts.
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 P20BF typically ranges from $50 to $150 for parts and labor, depending on whether the heater element or wiring needs replacement. If the PCM is faulty, costs can be higher.