Fuel trim: lean or rich
The mixture the ECU cannot correct for. Lean codes (P0171) usually mean unmetered air or a leaking exhaust before the sensor. Seeing lean AND rich together points at the sensor, not the mixture.
9 documented codes across 92 real diagnostics.
Ranked by how often we actually see them
| Code | What it is | Diagnostics |
|---|---|---|
| P0171 | System too lean, bank 1 | 60 |
| P0172 | System too rich, bank 1 | 10 |
| P2178 | System too rich off idle, bank 1 | 6 |
| P2188 | System too rich at idle, bank 1 | 4 |
| P2177 | System too lean off idle, bank 1 | 4 |
| P2187 | System too lean at idle, bank 1 | 3 |
| P0170 | Fuel trim, bank 1 | 3 |
| P2181 | Cooling system performance | 1 |
| P0174 | System too lean, bank 2 | 1 |
FAQ
Frequently asked questions
How do I run a diagnosis?
Select the vehicle on Start, click the Diagnostic card and choose New diagnostic. Fill in the description, the error codes and the mileage, then click Analyze.
Learn more: Diagnostic (vehicle-first start), Diagnostic form: description, error codes and mileage
Do I have to type the codes from my scan tool?
No. Click the camera button next to Error codes and take or choose a photo (JPEG or PNG) of the scan tool's screen; WrenchLane reads the codes and their descriptions into the form. You can also speak them with the microphone.
Learn more: OBD reader photo scan (fault codes from a photo), Voice input for the problem description
Are the public fault code pages built from my diagnostics?
They are built from anonymised, aggregated diagnostics run in WrenchLane; no workshop, customer or vehicle can be identified. Each fault code page shows how often the code was seen across those diagnostics and in how many separate workshops.
Learn more: Fault code pages on wrenchlane.com (fault-code cluster)
Work a fuel trim: lean or rich fault on a real car
Enter the codes and the symptoms and get ranked probable causes for that specific vehicle, with the checks in the order worth doing them. Free account, no card.
Start free