Reductant Purge Control Valve Stuck Open
The P20A4 code indicates that the reductant purge control valve, part of the selective catalytic reduction (SCR) system, is stuck open. This valve controls the flow of diesel exhaust fluid (DEF) from the tank to the injector. When stuck open, DEF can flow continuously, leading to over-injection, potential crystallization, and reduced system efficiency. This can cause increased emissions and trigger the check engine light.
01. Most Common Causes
- Faulty reductant purge control valve
- Electrical issues (shorted or open circuit in valve wiring)
- DEF contamination or crystallization causing valve to stick
- Corroded or damaged valve connector
02. Symptoms You Will Notice
- Check engine light illuminated
- Reduced engine performance or power
- Increased diesel exhaust fluid consumption
- Possible white smoke from exhaust due to over-injection
03. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm code P20A4 and check for related codes.
Step 2: Visually inspect the reductant purge control valve and its wiring for damage, corrosion, or loose connections.
Step 3: Test the valve's resistance with a multimeter; compare to manufacturer specs (typically 10-30 ohms).
Step 4: Activate the valve using a scan tool to verify it opens and closes properly.
Step 5: Check for DEF crystallization or contamination in the valve and lines; clean or replace as needed.
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 increased emissions and potential damage to the SCR system. You may experience reduced performance and the vehicle may enter limp mode.
How much does it cost to fix?▼
The cost to fix a P20A4 code typically ranges from $50 to $150 for parts and labor, depending on whether the valve needs replacement or just cleaning and if there are any wiring repairs needed.