Post Catalyst Fuel Trim System Too Rich Bank 1
The engine control module has detected a rich fuel condition after the catalyst on bank 1.
Heads up: this code wasn't in our hand-written library yet, so DiagCoach AI built this page on the fly. Double-check critical specs against service info before condemning parts.
What it means (plain English)
This code means the computer found too much fuel going into the exhaust after the catalytic converter on the first bank, indicating a problem with the fuel mixture being too rich.
What the computer is actually seeing
The engine computer monitors the oxygen sensor's voltage after the catalytic converter. In a normal scenario, this voltage fluctuates between 0.1V (lean) and 0.9V (rich). If it remains high (over 0.6V) for a certain period, it triggers this code.
What a healthy reading looks like
Oxygen sensor voltage for a healthy system should be between 0.1V and 0.9V, fluctuating. A steady high voltage indicates richness.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 11. Inspect the wiring and connector to the post-catalyst oxygen sensor for damage or corrosion. Fix as needed. Decision: If no issues found, proceed to step 2.
- 22. Check fuel trim readings with a scan tool. If fuel trim is not excessively positive (over 15% on long term), proceed to step 3. Decision: If fuel trim is high, diagnose fuel system issues (injectors, regulator).
- 33. Test the post-catalyst oxygen sensor with a multimeter. It should fluctuate when the engine is running. If it's steady and high, replace the sensor. Decision: If sensor is bad, replace it; if good, continue to step 4.
- 44. Inspect for vacuum and exhaust leaks. Use smoke testing if necessary. Decision: If leaks are found and repaired, reset codes and test drive. If not, continue diagnostics.
Common causes
- Faulty oxygen sensor (post-catalytic converter)
- Faulty fuel injectors
- Leaking fuel pressure regulator
- Vacuum leaks
- Exhaust leaks
- Faulty mass air flow (MAF) sensor
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
While the vehicle may still run, driving with a rich condition can damage the catalytic converter over time; it's best to fix it soon.
Will the code come back after clearing it?
If the underlying issue isn't resolved, the code is likely to return after a short drive.
Why does this code appear with other fuel trim codes?
Fuel trim codes often pair together as they all relate to the same issue: the air-fuel mixture being incorrect.
Working a real vehicle right now?
Let DiagCoach walk you through it live with your specific symptoms, vehicle, and what you've already checked.
Start guided diagnostic →