Reductant Heater Control Circuit Low
The P20BB code indicates that the powertrain control module (PCM) has detected a low voltage condition in the control circuit of the diesel exhaust fluid (DEF) heater. This heater is responsible for preventing DEF from freezing in cold temperatures. A low circuit condition typically means the voltage is below the expected threshold, which can be caused by a faulty heater element, damaged wiring, or a poor electrical connection.
1. Most Common Causes
- Faulty DEF heater element
- Open or shorted wiring in the heater control circuit
- Corroded or loose electrical connectors
- Failed PCM (rare)
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Reduced engine performance or limp mode
- Increased diesel exhaust fluid consumption
- Possible difficulty starting in cold weather
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 DEF heater wiring and connectors for damage, corrosion, or loose connections.
Step 3: Measure the resistance of the DEF heater element; compare to manufacturer specifications.
Step 4: Check for voltage and ground at the heater connector with the ignition on.
Step 5: If wiring and heater are okay, test the PCM output circuit for proper operation.
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 reduced engine performance, increased emissions, and potential damage to the DEF system. In some cases, the vehicle may enter limp mode.
How much does it cost to fix?▼
The cost to fix P20BB typically ranges from $50 to $150 for parts and labor, depending on the root cause. Replacing the DEF heater element or repairing wiring is usually straightforward.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.