Exhaust Aftertreatment Fuel Supply Control Circuit Low
The P20D9 code indicates that the powertrain control module (PCM) has detected a low voltage condition in the exhaust aftertreatment fuel supply control circuit. This circuit controls the fuel injector that supplies fuel to the diesel particulate filter (DPF) for regeneration. A low voltage reading suggests a short to ground, open circuit, or faulty component, which can prevent proper DPF regeneration and lead to increased emissions and potential engine performance issues.
1. Most Common Causes
- Post-treatment fuel injector (HC injector) internally shorted or open circuit
- HC injector control circuit wiring shorted to ground or open
- Corroded, loose, or damaged terminals at injector or PCM connectors
- Blown fuse in HC injector power supply circuit
- Internal PCM driver failure for the injector control
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Reduced engine performance or power
- Increased exhaust emissions
- Possible DPF regeneration issues
3. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm the code and check for related codes.
Step 2: Visually inspect the wiring and connectors for damage, corrosion, or loose connections.
Step 3: Test the fuel injector resistance with a multimeter and compare to specifications.
Step 4: Check for voltage and ground at the injector connector with the ignition on.
Step 5: If all else is okay, test the PCM output or consider a PCM update.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as it can cause DPF clogging and reduced engine performance. Immediate diagnosis is advised.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for diagnosis and minor repairs like wiring fixes, but injector replacement can be higher.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.