Reductant Heater Control Circuit Low
The P20C7 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 range, often due to a short to ground, open circuit, or faulty heater element. This can prevent the DEF system from operating correctly, leading to increased emissions and potential derate conditions.
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 power or derate mode
- Increased diesel exhaust fluid consumption
- Poor fuel economy
3. Step-by-Step Diagnosis
Step 1: Scan for additional codes and record freeze frame data.
Step 2: Visually inspect the DEF heater connector and wiring for damage, corrosion, or loose connections.
Step 3: Using a multimeter, check the resistance of the DEF heater element; compare to manufacturer specifications.
Step 4: Test the control circuit for voltage and ground integrity with the key on and engine off.
Step 5: If all checks pass, suspect a PCM fault and perform a PCM reflash or replacement if necessary.
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 power and potential damage to the DEF system. Short trips to a repair shop are generally acceptable.
How much does it cost to fix?▼
The cost to fix P20C7 typically ranges from $50 to $150 for diagnosis and simple repairs like connector cleaning or wiring repair. Heater element replacement can cost $200-$500 including parts and labor.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.