P2187 Engine computer sees a lean mixture on bank 1 at idle: too much air for the fuel being delivered

System too lean at idle, bank 1

Monitor

A lean code is an emissions and drivability fault; the sources describe a lit check engine light with possible rough running, misfire or stalling, so it can usually be driven briefly while you book a check, but it should not be left.

It gets more serious if:

  • Inspect soon: Inspect soon if the engine stalls at idle, hard-starts when hot, misfires or loses power. TroubleCodes.net lists stalling and hard hot starting, and a Mercedes CLA owner reports the car losing power and lighting warning lamps after fuelling.

Source: how we rate severity

P2187 in short

P2187 means the engine computer found too much air for the fuel on bank 1 at idle. Common causes are an intake or vacuum leak, a dirty airflow sensor, a faulty upstream oxygen sensor or its wiring, and weak fuel delivery. Get it checked if the engine stalls or loses power.

The engine computer holds the idle mixture steady by adjusting fuel from the exhaust sensor reading. P2187 sets when it has added as much fuel as it can at idle on bank 1 and the exhaust still shows too much air.

At idle even a small leak matters, because little air normally passes the throttle. That is why intake, vacuum, crankcase and EVAP leaks head the cause lists, along with weak fuel delivery and sensor problems.

Several makers have specific findings. Audi ties P2187 on 2005-2010 A3, A4 and TT to an intake air leak, Land Rover to a split camshaft cover pressure-control valve diaphragm, GM to exhaust leaks at the turbo and converter flange on the Solstice and Sky, and Mazda to a damaged air-fuel sensor harness cover on the CX-7.

Most likely causes

  1. Air leak: intake, vacuum, crankcase or EVAP lines

    Common general cause
    Why it ranks here
    TroubleCodes.net lists vacuum, inlet manifold, EVAP, brake supply and crankcase (PCV) leaks first, and Kelley Blue Book lists vacuum leaks. Audi and Land Rover bulletins name intake air leaks for this code.
    What would change this
    Rises if smoke finds a leak, you hear air rushing, or fuel trim is far positive at idle and falls with rpm. Falls if the intake and crankcase hold smoke.
    How to test the vacuum hoses and intake leaks

  2. Contaminated or faulty mass airflow or MAP sensor

    Common general cause
    Why it ranks here
    Both references list the airflow sensor; TroubleCodes.net says to check it for oil contamination.
    What would change this
    Rises if the sensor is oily or its readings disagree with expected idle airflow. Falls if airflow readings look right.
    How to test the mass airflow (maf) sensor

  3. Low fuel pressure: pump, regulator, filter or injectors

    Common general cause
    Why it ranks here
    TroubleCodes.net lists a faulty regulator, pump or clogged filter and Kelley Blue Book lists a weak fuel pump or clogged filter. A 2018 Honda Accord complaint reports P2187 with a fuel rail replacement.
    What would change this
    Rises if measured fuel pressure is below specification. Falls if pressure is normal at idle and under load.
    How to test the fuel pump

  4. Upstream oxygen or air-fuel sensor or its wiring

    Supported by vehicle data
    Why it ranks here
    Both references list the upstream sensor and wiring. Mazda bulletin 01-009-13-2764 traces P2187/P2177 on CX-7s to a damaged air-fuel sensor harness cover.
    What would change this
    Rises if the harness is damaged or the sensor responds slowly. Falls if wiring is intact and response is quick.
    How to test the oxygen (o2) sensor

  5. Exhaust leak near the upstream sensor

    Supported by vehicle data
    Why it ranks here
    Both references list exhaust leaks, because outside air at the sensor reads as lean. GM PIP4075A tells technicians to inspect the turbo and converter exhaust mating surfaces for the P2187 diagnosis on the 2007 Solstice and Sky.
    What would change this
    Rises if soot trails or a ticking sound are found at flanges ahead of the sensor. Falls if the exhaust is tight.

What to test first

Start at step 1. Each result tells you what it means and where to go next.

  1. Read all stored and pending codes and freeze-frame data, and record fuel trims at idle. Fix other lean, misfire or sensor codes first.

    Low riskTool: OBD-II scan tool

    • IfOnly P2187 (maybe with P2177) is stored

      It meansLook for an air leak first.

      Go to step 2

    • IfOther fuel, misfire or sensor codes are present

      It meansTreat those first; they can cause the lean code.

  2. Inspect vacuum, intake and crankcase hoses and the intake tract for splits and loose clamps, then have the system smoke-tested.

    Best left to a shopTool: smoke machine

    Warning:Smoke testing is done with the engine running or the intake pressurised, near the hot exhaust manifold and moving belts. A shop should do it.

  3. Check the airflow sensor for oil or dirt, then measure fuel pressure against specification.

    Best left to a shopTool: scan tool, fuel pressure gauge

    Warning:Connecting a gauge releases fuel near hot parts and ignition sources; leave it to a shop.

  4. Inspect exhaust joints ahead of the upstream sensor for leaks, and check the sensor wiring and response.

    Use cautionTool: scan tool, multimeter

    Warning:Exhaust parts stay hot long after the engine stops. Let the car cool for at least an hour and never work under a car held only by a jack.

Symptoms

  • Check engine light
  • Rough or fluctuating idle Gets more serious: stop and have it checked.
  • Stalling at idle, or hard starting when hot Gets more serious: stop and have it checked.
  • Misfire or hesitation Gets more serious: stop and have it checked.
  • Whistling or air-rushing noise from the engine (Audi bulletin)

Compare with: Rough idle with the check engine light on, Check engine light with loss of power

How to fix

  1. With the engine off and cool, look over the intake duct and vacuum and crankcase hoses for cracks, splits or loose clamps, and make sure the oil filler cap is seated.

  2. If the airflow sensor looks oily or dirty and your maker allows cleaning, spray only the sensing element with dedicated MAF sensor cleaner, never touch it, and let it dry fully before reconnecting.

    Warning:Disconnect the sensor before cleaning, use only cleaner made for MAF sensors, and do not refit it wet.

Parts and cost context

  • Vacuum hoses and intake leaks:Hoses, boots and crankcase vent parts are usually inexpensive; finding the leak is most of the job.
  • Mass airflow (MAF) sensor:Try an approved cleaning first and use the correct sensor for your engine.
  • Fuel pump:Replace only after a pressure test shows it weak; fuel work carries fire risk.
  • Oxygen (O2) sensor:Replace only after a response test or visible harness damage.

Labor varies by vehicle and shop; get a quote before you approve a repair.

Compare used part prices on PartPriceGuide

On your vehicle

Mazda

  • 2007–2009 · CX-7

    Supported by vehicle data

    Mazda ties P2187/P2177 on some CX-7s to damaged air-fuel sensor harness covers; check the harness early.

  • 2004–2005 · Mazda3

    Supported by vehicle data

    Mazda has a bulletin for P2177/P2187 on 2004-2005 Mazda3; whether it is current is not verified.

  • 01-009-13-2764Status unverified

    Lack of power with MIL, P2187/P2177 (A/F sensor harness cover)

    2007–2009cx-7 · issued · NHTSA 10097317

    Mazda lists P2187 as fuel system too lean at idle and says brake fluid spilled during earlier work can damage the A/F sensor wire cover and short the shield wire; a short cord with shield wire was set up for the repair.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • 01-022-08Status unverified

    Rough idle, lack of power or MIL with P2177/P2187

    2006–2008cx-7, mazdaspeed3, mazdaspeed6 · issued · NHTSA 10024621

    Mazda bulletin for rough idle, lack of power or MIL with P2177/P2187 (fuel system lean). The summary gives no cause or repair.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

  • 03012005Status unverified

    MIL on with P2177 / P2187 set

    2004–2005mazda3 · issued · NHTSA 10015727

    Mazda bulletin for a MIL with P2177 and P2187 on Mazda3. The summary gives no cause or repair.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Audi

  • 2005–2009 · A4

    Supported by vehicle data

    Audi bulletin 2015505-10 links P2187 on A3, A4 and TT to an intake air leak, with a possible whistle noise.

  • 2015505-10Status unverified

    MIL on (P1297, P2187, P2279), oil leaks, pressure loss, intake air leak

    2005–2010a3, a4, tt · issued · NHTSA 10043872

    Audi ties P2187 and system too lean at idle to an intake air system leak, with possible whistle or air-rushing noise and oil leaks. The summary does not give the repair.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Pontiac

  • 2007 · Solstice

    Supported by vehicle data

    GM says to check the turbo and converter exhaust joints for leaks as part of the service-manual P2187 diagnosis.

  • PIP4075A (pontiac)Status unverified

    Supplement to P2187 diagnosis: exhaust leak at turbo and converter

    2007solstice · issued · NHTSA 10156959

    GM tells the technician to inspect the turbocharger and catalytic converter exhaust mating surfaces for leakage as part of the P2187 diagnosis.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Saturn

  • PIP4075A (saturn)Status unverified

    Supplement to P2187 diagnosis: exhaust leak at turbo and converter

    2007sky · issued · NHTSA 10156959

    GM tells the technician to inspect the turbocharger and catalytic converter exhaust mating surfaces for leakage as part of the P2187 diagnosis.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Land Rover

  • 2005–2019 · Range Rover Sport

    Supported by vehicle data

    Land Rover names a split camshaft cover pressure-control valve diaphragm as an air leak that can store P2187.

  • SSM74374Status unverified

    Air leak at right camshaft cover pressure control valve

    2005–2019range-rover, range-rover-sport, discovery, lr3 · issued · NHTSA 10160434

    Land Rover names an air leak from the right camshaft cover assembly, due to a split diaphragm in the pressure control valve, with P2187, P2189, P0505 or P0507 possibly stored in the PCM.

    We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

Mercedes-Benz

  • 2016 · CLA-Class

    Possible — needs testing

    A 2016 CLA250 owner reports P2187 (Bank 1) with lights and loss of power after fuelling. This is a single complaint.

  • P2177Engine computer sees a lean mixture on bank 1 off idle (while cruising or at light throttle): too much air for the fuel being delivered

    Same system Supported by vehicle data

    P2177 is the same bank 1 lean test off idle; Mazda bulletins list the two together.

  • P0171Engine computer has reached its limit adding fuel on bank 1: the mixture is lean

    Same system Common general cause

    P0171 is the general bank 1 lean code with overlapping causes.

All Fuel trim (air-fuel mixture) codes

P2187 questions

What is the difference between P2187 and P2177?

Both are bank 1 lean codes. P2187 sets at idle and P2177 sets off idle. A leak or fuel delivery problem can set both.

Why does P2187 point so often to leaks?

At idle very little air passes the throttle, so a small leak is a big share of the total air and tips the mixture lean. Intake, vacuum, crankcase and EVAP leaks all appear in the cause lists.

Sources and review

  1. TroubleCodes.net P2187 System Too Lean at Idle, Bank 1 — TroubleCodes.net
  2. Kelley Blue Book OBD-II code P2187 — Kelley Blue Book
  3. NHTSA complaints ODI 11638804 (2016 Mercedes-Benz CLA250), 10448600 (2006 Volkswagen Passat) and 11464010 (2018 Honda Accord) — NHTSA ODI
  4. Audi bulletin 2015505-10: MIL on (P1297, P2187, P2279), oil leaks, pressure loss, intake air leak — Audi via NHTSA
  5. Land Rover SSM74374: air leak at right camshaft cover pressure control valve — Jaguar Land Rover via NHTSA
  6. Mazda bulletin 01-009-13-2764: lack of power, MIL and P2187/P2177 on CX-7 — Mazda via NHTSA
  7. GM PIP4075A: supplement to the P2187 diagnosis (turbocharger and catalytic converter exhaust mating surfaces) — General Motors via NHTSA
  8. Mazda bulletin 01-022/08: rough idle, lack of power or MIL with P2177/P2187 (fuel system lean) — Mazda via NHTSA
  9. Mazda bulletin 03012005: MIL on with P2177/P2187 set on Mazda3 — Mazda via NHTSA
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Written by
Saurabh K.
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