Reductant Control Module Requested MIL Illumination
The P20C9 code indicates that the reductant control module (RCM) has detected a fault in the selective catalytic reduction (SCR) system, such as incorrect DEF quality, insufficient DEF flow, or a malfunctioning sensor, and has requested the malfunction indicator lamp (MIL) to illuminate. This is typically related to diesel exhaust fluid (DEF) system issues in diesel vehicles.
01. Most Common Causes
- Faulty reductant control module
- Poor quality or contaminated DEF fluid
- DEF injector or pump malfunction
- Wiring or connector issues in the SCR system
02. Symptoms You Will Notice
- Check Engine Light on
- Reduced engine performance or power
- Increased emissions
- Possible limp mode activation
03. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm the code and check for related codes.
Step 2: Inspect DEF fluid level and quality; replace if contaminated.
Step 3: Check wiring and connectors to the reductant control module for damage or corrosion.
Step 4: Test the DEF injector and pump for proper operation.
Step 5: If all else fails, replace the reductant control module.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as it may lead to reduced performance, limp mode, or further damage to the SCR system. 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 fluid replacement, but can be higher if the control module or injectors need replacement.