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P2187 on a 2017 Honda Civic

System Too Lean at Idle (Bank 1)

P2187 on a 2017 Honda Civic indicates system too lean at idle (bank 1). It usually stays drivable short-term but should be diagnosed promptly. The most common cause is vacuum leak (intake gasket, brake-booster hose, pcv, throttle-body gasket) (typically $80–$600). Confirm the root cause before replacing parts.

Severity: moderate Safe to drive (short term) Compact Sedan 2015-2019 Honda Civic

Reviewed by MECH AI Editorial · Last verified · Includes 20 active NHTSA TSBs

What does P2187 mean on a 2017 Honda Civic?

P2187 is set when long-term fuel trim on Bank 1 goes excessively positive (typically beyond +20 %) specifically at idle, but stays closer to normal at part-throttle and cruise. The distinctive pattern — lean only at idle — almost always points at a vacuum leak rather than a fueling problem. At idle, intake manifold vacuum is at its highest, which amplifies the effect of any leak; off-idle, the leak path becomes a smaller fraction of total airflow and trims look fine.

This guide covers P2187 across the 2015-2019 Honda Civic generation — the symptoms, causes, and diagnostic steps below apply to every model year from 2015 through 2019.

Is it safe to drive a 2017 Honda Civic with P2187?

In most cases a 2017 Honda Civic stays drivable for short trips with P2187 active, but diagnose and repair it promptly. This is a moderate-severity code — ignoring it can lead to further damage or a failed emissions test.

What are the symptoms of P2187 on a 2017 Honda Civic?

What causes P2187 on a 2017 Honda Civic?

Cause Likelihood Estimated repair (USD)
Vacuum leak (intake gasket, brake-booster hose, PCV, throttle-body gasket) P2187 is essentially "lean at idle = vacuum leak" until proven otherwise. Most common $80–$600
Stuck-open EVAP purge valve introducing fuel vapor unmanaged Common $80–$300
Cracked plastic intake manifold (Ford 4.6/5.4, Chrysler 4.0, GM 3.6) Common $250–$900
Failing PCV valve or hose Common $30–$200
Failed or biased Bank 1 upstream O2 sensor Occasional $150–$450
Throttle body gasket leak Occasional $30–$200
Carbon-coked throttle body letting blade hold slightly open Occasional $20–$200

How to diagnose this on a 2017 Honda Civic

  1. Compare idle vs cruise fuel trims

    Read Bank 1 LTFT at idle and at 2500 RPM cruise. P2187 with LTFT around +20 % at idle but near zero at cruise is the classic vacuum-leak signature. P2187 with high trim at all RPMs is a broader lean condition (likely P0171 alongside).

    Tools: Scan tool with live PIDs

  2. Smoke-test the intake comprehensively

    Pressurize the intake with smoke through the throttle body. Watch every gasket, hose, vacuum tee, the brake booster line, the PCV system, the EVAP purge line, and any unused vacuum ports. The leak path is somewhere in there.

    Tools: EVAP / intake smoke machine, Flashlight and mirror

  3. Inspect the PCV system

    The PCV system is a common P2187 cause — particularly the hose from the valve cover to the intake. Aged rubber cracks and PCV valves stick open. Pull the valve and shake — it should rattle. A non-rattling PCV is finished.

    Tools: Common hand tools

  4. Disconnect the EVAP purge to test

    With the engine warm and idling, disconnect the purge valve. If the rough idle smooths out and LTFT drops, the purge valve was stuck open. P2187 + idle improvement on purge disconnect = purge valve.

    Tools: Hose disconnect tools

  5. Inspect the brake booster hose

    A failing brake booster diaphragm or hose is the single most overlooked P2187 cause. Pull the brake-booster line off and cap the manifold port. If idle smooths out, the booster or its hose is the leak.

    Tools: Hose plug or vacuum cap

Known Technical Service Bulletins for the 2015-2019 Honda Civic

Manufacturers publish Technical Service Bulletins (TSBs) when a known issue affects a specific vehicle. These bulletins come from the NHTSA database for your Honda Civic.

+14 more TSBs available in MECH AI's TSB explorer for this vehicle.

NHTSA complaints & recalls for the 2017 Honda Civic

Owner-reported safety complaints and official recalls filed with the U.S. National Highway Traffic Safety Administration for the 2017 Honda Civic. Use these to gauge how common a problem is on your specific vehicle before you start chasing Honda Civic diagnostics.

569 owner complaints
22 involved a crash
6 involved a fire
11 reported injuries
  • ENGINE 65
  • STEERING 161
  • UNKNOWN OR OTHER 160
  • ELECTRICAL SYSTEM 99
  • SERVICE BRAKES 35

6 active recalls

  • STEERING:ELECTRIC POWER ASSIST SYSTEM Sep 2018

    Honda (American Honda Motor Co.) is recalling certain 2017-2018 Honda Civic and CR-V vehicles. The magnet that controls the torque sensor output signal for the electronic power steering system may not be properly secured, allowing the magnet to become dislodged. During a full…

    NHTSA campaign 18V663000
  • EQUIPMENT:OTHER:OWNERS/SERVICE/OTHER MANUAL Nov 2018

    Honda (American Honda Motor Co.) is recalling certain 2017-2018 Honda Civic Hatchback and Civic Type R vehicles. The owners guide in these vehicles may not have been included or if included, the owner's guide may not have been properly provided required information. As such, t…

    NHTSA campaign 18V817000
  • AIR BAGS Apr 2018

    Honda (American Honda Motor Co.) is recalling certain 2017 Honda Civic Hatchback and Civic Type R vehicles. Driver and front passenger seatback pads sold as replacement service parts were made without slit openings for the seat-mounted side air bags. In the event of a crash nece…

    NHTSA campaign 18V266000
  • POWER TRAIN:DRIVELINE:DRIVESHAFT Nov 2017

    Honda (American Honda Motor Co.) is recalling certain 2017 Honda Civic Sedan and Coupe vehicles. The right halfshaft may have been improperly heat treated, reducing its strength.…

    NHTSA campaign 17V706000

How do I fix P2187 on a 2017 Honda Civic?

About the 2015-2019 Honda Civic

The 2015-2019 Honda Civic was commonly sold with the following powertrains: 2.0L I4, 1.5L Turbo I4, 1.8L I4. Common trims include LX, Sport, EX, Touring.

Why “lean at idle but not at cruise” points at a vacuum leak

The size of any intake vacuum leak is fixed — say, 5 grams per minute of air. At idle, the engine consumes maybe 15 g/s of air total. The leak represents a big fraction of that total, so fuel trim has to add fuel aggressively to compensate. At cruise the engine consumes 100+ g/s of air; the same leak is now proportionally tiny and trim looks normal.

This is why P2187 specifically (lean at idle) is so reliably a vacuum leak diagnosis — far more so than the broader P0171 which could also be fuel-side problems.

P2187 vs P0171

If both codes set together, the vacuum leak is large enough to affect cruise trim too. If only P2187 sets, the leak is small.

Common P2187-prone vehicles

P2187 on a 2017 Honda Civic: frequently asked questions

What does diagnostic trouble code P2187 mean on a 2017 Honda Civic?

P2187 is set when long-term fuel trim on Bank 1 goes excessively positive (typically beyond +20 %) specifically at idle, but stays closer to normal at part-throttle and cruise. The distinctive pattern — lean only at idle — almost always points at a vacuum leak rather than a fueling problem. At idle, intake manifold vacuum is at its highest, which amplifies the effect of any leak; off-idle, the leak path becomes a smaller fraction of total airflow and trims look fine.

What are the symptoms of P2187 on a 2017 Honda Civic?

Check Engine Light is illuminated. Rough or unstable idle, especially when warm. Possible hesitation or stumble immediately off-idle. Stalling at idle (worst cases). Slight reduction in fuel economy. May be paired with P0171 (general lean Bank 1) if the leak is large. No drivability issue at cruise

What causes P2187 on a 2017 Honda Civic?

Vacuum leak (intake gasket, brake-booster hose, PCV, throttle-body gasket) (most-common). Stuck-open EVAP purge valve introducing fuel vapor unmanaged (common). Cracked plastic intake manifold (Ford 4.6/5.4, Chrysler 4.0, GM 3.6) (common). Failing PCV valve or hose (common). Failed or biased Bank 1 upstream O2 sensor (occasional). Throttle body gasket leak (occasional). Carbon-coked throttle body letting blade hold slightly open (occasional)

Is it safe to drive a 2017 Honda Civic with P2187?

In most cases a 2017 Honda Civic stays drivable for short trips with P2187 active, but it should be diagnosed and repaired promptly — this is a moderate-severity code. Ignoring it can lead to further damage or a failed emissions test.

Related diagnostic codes

P2187 on other Honda Civic model years