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 voltage typically points to a wiring issue, a faulty valve, or a problem with the PCM. This can lead to improper DEF injection, increased emissions, and potential damage to the SCR system.
1. Most Common Causes
- Faulty reductant injection air pressure control valve
- Open or shorted wiring in the valve circuit
- Poor electrical connection at the valve or PCM
- Failed PCM (rare)
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Reduced engine performance or power
- Increased exhaust emissions
- Possible DEF system warning messages
3. Step-by-Step Diagnosis
Step 1: Use a scan tool to retrieve all stored codes and freeze frame data.
Step 2: Visually inspect the wiring and connectors for damage, corrosion, or loose connections.
Step 3: Test the valve's resistance and compare to manufacturer specs.
Step 4: Check for voltage and ground at the valve connector with the ignition on.
Step 5: If all tests pass, suspect a faulty PCM and perform further diagnostics.
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 increased emissions and potential damage to the SCR system. However, short trips to a repair shop are generally acceptable.
How much does it cost to fix?▼
The cost to fix P20A8 typically ranges from $50 to $150 for diagnosis and repair, depending on the root cause. Replacing the valve can cost $100-$300, while wiring repairs are usually less expensive.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.