P2187 means System Too Lean at Idle (Bank 1). At idle, the computer is adding more fuel than its limit on bank 1 and still seeing a lean mixture. It is a generic OBD-II code, so the definition is the same on any make, but the most likely cause varies by engine; confirm with a scan tool and the service information for your vehicle before buying parts.
What P2187 means
The engine computer keeps adjusting fuel to hold the air-fuel mixture near the ideal ratio, using oxygen sensor feedback. Those adjustments are fuel trims: short-term trim reacts instantly and long-term trim learns over time. Positive numbers mean the computer is adding fuel; negative numbers mean it is taking fuel away. When long-term trim sits near the limit the computer allows, it sets a lean or rich code. On a V engine, bank 1 is the side containing cylinder 1 and bank 2 is the opposite side; inline engines only have bank 1.
P2187 symptoms
- Check engine light
- Rough or unstable idle
- Hesitation from a stop
Common causes of P2187
- Vacuum leak, which matters most at idle
- Leaking PCV hose or valve
- Dirty MAF sensor
- Low fuel pressure
How to diagnose P2187
- Check fuel trims at idle and at 2,500 rpm
- Smoke-test the intake for leaks
- Inspect the PCV system
- Clean or test the MAF sensor
Can you drive with P2187?
Usually yes, but find vacuum leaks soon.
P2187 tips
Because a fixed vacuum leak is a bigger share of total airflow at idle, P2187 without matching trims at higher rpm strongly suggests a vacuum leak.
Will P2187 clear itself?
If the fault stops, the computer turns off the check engine light by itself after several drive cycles without seeing it again, and the code stays in memory as history for a while. Clearing P2187 with a scan tool after a repair is fine, but if the cause is still there the code returns, sometimes within one drive. Disconnecting the battery also clears codes on most vehicles, but it erases learned fuel trims and idle settings as well.
Related codes
| Code | Meaning |
|---|---|
| P0171 | System Too Lean (Bank 1) |
| P2188 | System Too Rich at Idle (Bank 1) |
| P0101 | Mass or Volume Air Flow Circuit Range/Performance |
Guides that help
When it is more than a sensor
Fuel trim codes are almost always fixed with a leak repair, a sensor or a fuel delivery part. If a long-running lean condition has burned a valve or piston and a compression test confirms it, compare repair against a replacement on our engines page and see engine replacement cost.
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