Reductant Heater Control Circuit Low Voltage
The P202B code indicates that the powertrain control module (PCM) has detected a low voltage condition in the reductant tank heater control circuit. This heater is part of the selective catalytic reduction (SCR) system, which uses diesel exhaust fluid (DEF) to reduce NOx emissions. The heater prevents DEF from freezing in cold temperatures. A low voltage reading suggests a short to ground, open circuit, or faulty heater element, which can prevent proper DEF delivery and increase emissions.
1. Most Common Causes
- Faulty reductant tank heater element
- Open or shorted wiring in the heater control circuit
- Corroded or damaged connector at the heater
- Failed PCM (rare)
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Reduced engine power or limp mode
- Increased diesel exhaust fluid consumption
- Failed emissions test
3. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm P202B and check for related codes.
Step 2: Visually inspect the reductant tank heater connector and wiring for damage or corrosion.
Step 3: Measure resistance of the heater element; compare to manufacturer specs (typically 0.5-5 ohms).
Step 4: Check for voltage at the heater connector with the ignition on; should be battery voltage.
Step 5: If voltage is low, test the control circuit for shorts or opens using a multimeter.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
You can drive short distances, but continued operation may cause reduced engine power, increased emissions, and potential damage to the SCR system. It's best to repair promptly.
How much does it cost to fix?▼
Repair costs range from $150 to $400, including parts (heater element or wiring repair) and labor. PCM replacement is rare and more expensive.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.