Reductant Consumption Too High
The P20F4 code indicates that the Diesel Exhaust Fluid (DEF) consumption is higher than expected by the engine control module. This is often due to a malfunctioning DEF injector, a leak in the DEF system, or incorrect dosing strategy. The system monitors the amount of reductant used and compares it to the expected amount based on driving conditions. When the actual consumption exceeds the threshold, this code is set.
01. Most Common Causes
- Faulty DEF injector causing over-dosing
- Leak in DEF supply lines or tank
- DEF quality issue (contaminated or incorrect concentration)
- Malfunctioning NOx sensor providing false readings
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Reduced engine performance or power
- Increased DEF consumption
- Possible limp mode activation
03. Step-by-Step Diagnosis
Step 1: Scan for additional codes and freeze frame data.
Step 2: Visually inspect DEF system for leaks, damage, or loose connections.
Step 3: Check DEF quality using a refractometer or test strip.
Step 4: Perform a DEF injector flow test using a scan tool to compare commanded vs actual flow.
Step 5: Inspect NOx sensor readings and compare to expected values.
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 eventual inability to start. Short trips to a repair shop are acceptable.
How much does it cost to fix?▼
Diagnosis typically costs $50-$150. Repairs vary: a DEF injector replacement can be $200-$500, while fixing a leak may be $100-$300.