Reductant Heater Control Circuit Low
The P20C3 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 the DEF from freezing in cold temperatures, ensuring proper operation of the selective catalytic reduction (SCR) system. A low circuit condition typically points to a short to ground, open circuit, or a faulty heater element, which can lead to reduced NOx reduction efficiency and potential emissions system issues.
01. Most Common Causes
- Faulty DEF heater element
- Short to ground in the heater control circuit
- Open or damaged wiring/connectors
- Failed PCM (rare)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Reduced fuel economy
- Increased diesel exhaust fluid consumption
- Possible engine derate or limp mode
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to retrieve freeze frame data and confirm the code.
Step 2: Visually inspect the DEF heater wiring and connectors for damage, corrosion, or loose connections.
Step 3: Measure resistance of the DEF heater element; compare to manufacturer specifications (typically 0.5-2 ohms).
Step 4: Check for voltage at the heater connector with the ignition on; should be battery voltage. If low, check for shorts or opens in the circuit.
Step 5: If all checks pass, test the PCM output or replace the heater assembly.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is generally not recommended to drive long distances with this code, as it can lead to reduced emissions system performance and potential engine derate. However, short trips may be possible if the DEF heater is not needed (e.g., warm weather).
How much does it cost to fix?▼
The cost to fix P20C3 typically ranges from $50 to $150 for parts and labor, depending on whether it's a simple wiring repair or a heater replacement. Diagnostic fees may add $50-$100.