Reductant Injection Air Pressure Control Valve Circuit Low
The P20A8 code indicates that the powertrain control module (PCM) has detected a low voltage condition in the reductant injection air pressure control valve circuit. This valve is part of the selective catalytic reduction (SCR) system, which injects diesel exhaust fluid (DEF) into the exhaust stream to reduce NOx emissions. A low circuit signal suggests a short to ground, open circuit, or faulty valve, potentially causing insufficient DEF injection and increased emissions.
01. Most Common Causes
- Faulty reductant injection air pressure control valve
- Open or shorted wiring in the valve circuit
- Corroded or damaged electrical connector
- Failed PCM (rare)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Reduced engine performance or power
- Increased diesel exhaust fluid consumption
- Failed emissions test
03. Step-by-Step Diagnosis
Step 1: Scan for additional codes and record freeze frame data.
Step 2: Visually inspect the valve and wiring for damage, corrosion, or loose connections.
Step 3: Use a multimeter to check voltage and resistance at the valve connector per manufacturer specs.
Step 4: Test the valve by applying battery voltage and ground to verify operation.
Step 5: If wiring and valve are OK, check PCM for faults or update software.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is generally safe to drive short distances, but prolonged driving may cause increased emissions and potential damage to the SCR system. It's best to diagnose and repair promptly.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for parts and labor, depending on whether the valve or wiring needs replacement.