Number P2187: System Too Lean at Idle (Bank 1)
P2187 means the long-term fuel trim of bank 1 has to add more fuel than allowed in the idle and low-load range. Many systems, especially Bosch ones, split mixture adaptation into an additive part, which dominates at low airflow, and a multiplicative part for load. An air leak adds a fixed amount of
Can you drive with P2187?
Severity: Plan the repair. Yes — this is an emissions-system fault. The car will generally drive normally, but it will fail an emissions inspection with the light on.
If you ignore it: Fuel economy and emissions creep up, and some faults in this family (rich/lean running) stress the catalyst over time.
This is the #91 most common code in our top-150 library, in the fuel trim & air metering family (Powertrain system). Severity is Number Nest's editorial triage — if the light is flashing or the car feels unsafe, stop driving it whatever any page says.
What P2187 means
P2187 means the long-term fuel trim of bank 1 has to add more fuel than allowed in the idle and low-load range. Many systems, especially Bosch ones, split mixture adaptation into an additive part, which dominates at low airflow, and a multiplicative part for load. An air leak adds a fixed amount of unmeasured air, which matters most at idle, so it shows up in the additive part. GM's 3.6 V6 engines set the code above 7 % (2005) or 6.1 % (2008 LLT, at 520 to 1120 rpm, 1.7 to 7.8 g/s and coolant above 60 °C), and GM's 2024 tables above about 5.5 %, over two trips. On the Opel/GM 2.0 turbo in the Saab 9-5 (2010) the weighted long-term trim must exceed its limit for 4 s continuously or 50 s in total (Type B). Audi traced P2187 with P2279 on 2.0 TFSI engines to a crankcase ventilation valve that let boost into the crankcase; Mazda found A/F sensor wiring on the CX-7 2.3 turbo shorted after brake fluid was spilled on it.
Systems involved: intake manifold, pcv valve, vacuum hoses, mass air flow sensor, oxygen sensor upstream.
Causes, ranked by likelihood
| # | Cause | Likelihood |
|---|---|---|
| 1 | Air leak after the air mass sensor, often at the crankcase ventilation | most likely |
| 2 | Damaged front oxygen or A/F sensor wiring | less common |
| 3 | Fuel pressure too low | less common |
Check them in order — the list is ranked so the likely, cheaper causes come before the expensive part.
Symptoms you may notice
- Malfunction indicator lamp on
- Rough or hunting idle, hissing from the engine bay
Misdiagnosis traps
- Replacing the part named by the code title without testing. The code reports a failed self-test; the cause list above is ranked so the likely, cheap causes are checked before the expensive part is condemned.
- Clearing the code and declaring victory when the light stays off for a day — the monitor that sets this code runs only under specific driving conditions.
(General diagnostic guidance for this code family — no code-specific trap is published for this code.)
How a good shop confirms it
- Confirm the code and record any companion codes — companions narrow the system fast.
- Inspect the affected components and their wiring/connectors for damage, corrosion and looseness.
- Test the top-ranked cause with live data or a multimeter before replacing anything.
(Standard diagnostic path for this family, labeled as general guidance.)
Repair options & costs
| Repair | Shop total (parts + labor) | DIY (parts only) | Difficulty |
|---|---|---|---|
| Mass air flow (MAF) sensor | $158 – $420 | $120 – $320 (parts only) | 1/5 |
| Intake / vacuum leak repair (gaskets, hoses) | $338 – $838 | $150 – $400 (parts only) | 3/5 |
National ranges from Number Nest's cost model (midsize car, independent shop, US-average labor). Published cross-check — Mass air flow (MAF) sensor: CarMD 2026 national average $346.
OBDex repair data for this code rates the job difficulty medium with a typical labor time in the 0.5–2.5 hour range and DIY possible: yes.
Price this repair in your state
Estimated total: — (midsize car, independent shop)
Frequently asked questions
How much does it cost to fix P2187?
The fix most associated with this code — mass air flow (maf) sensor — runs $158 – $420 at an independent shop for a midsize car in our cost model (parts + labor, US average). The code names a system, not a part, so confirm the cause before spending: the ranked causes above are ordered by likelihood.
Can I drive with P2187?
See the can-you-drive verdict above — it is based on the system involved and the cascading-damage risk, and it is our editorial triage, not a manufacturer instruction. If the light is flashing or the car feels unsafe, stop driving it regardless of any code.
Will P2187 clear itself?
If the fault was a one-off (a loose cap, a cold-start glitch), the light can go out after several clean trips and the code ages into history. A fault that is still present re-sets the code as soon as the car runs that self-test again — monitors run under specific conditions, which is why "it hasn't come back in two days" is not proof of a fix.
Will my car fail inspection with P2187?
In states with OBD-based emissions inspection, yes — an illuminated check-engine light or an incomplete readiness monitor fails the test regardless of what the tailpipe would show. C-codes (ABS) fall under safety inspection instead in states that have one.
What should I check first for P2187?
The first item on the ranked-causes list above — it is ranked likelihood-first for exactly this reason — plus the free checks: recent work in the area (connectors left loose are a classic), fluid levels, and the battery and grounds on electrical codes.
Where this data comes from
Code facts, causes and symptoms come from OBDex — an open dataset of independently authored descriptions of the standardized generic OBD-II codes (CC0 1.0, public domain; github.com/foerbsnavi/OBDex). The SAE J2012 document itself is copyrighted and is not reproduced here. Cost ranges are Number Nest's own US planning model: national parts and labor ranges cross-checked against the CarMD Vehicle Health Index 2026 published averages, with labor adjustable by the BLS OEWS May 2025 state wage index for auto technicians (occupation 49-3023) — a wage index, not a surveyed shop rate. Severity and can-you-drive notes are our editorial triage, not a manufacturer instruction.