SCR NOx Pre-Catalyst Over Temperature Bank 1
The P20ED code indicates that the Selective Catalytic Reduction (SCR) system's pre-catalyst NOx sensor on Bank 1 has detected an exhaust temperature exceeding the maximum allowable limit. This can be caused by excessive fuel in the exhaust, a malfunctioning diesel particulate filter (DPF) regeneration process, or a faulty temperature sensor. Overheating can damage the SCR catalyst and downstream components.
1. Most Common Causes
- Faulty NOx sensor or temperature sensor
- Excessive fuel in exhaust due to injector leak or over-fueling
- Malfunctioning DPF regeneration causing high temperatures
- Exhaust restriction or clogged catalyst
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Reduced engine performance or limp mode
- Increased exhaust smoke
- Poor fuel economy
3. Step-by-Step Diagnosis
Step 1: Scan for additional codes and freeze frame data.
Step 2: Inspect exhaust system for leaks, restrictions, or damage.
Step 3: Check NOx sensor and temperature sensor readings with a scan tool.
Step 4: Perform a DPF regeneration test and monitor exhaust temperatures.
Step 5: Test fuel injectors for leaks or over-fueling.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
No, driving with an over-temperature condition can damage the SCR catalyst and other exhaust components. It is recommended to address the issue promptly.
How much does it cost to fix?▼
Repair costs vary from $150 to $600 depending on the root cause, such as sensor replacement or injector repair.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.