P2187: System Too Lean at Idle (Bank 1)

What does P2187 mean?

At idle the engine takes in little air, so even a small unmetered air leak has a big effect on the mixture. When the ECM adds fuel to its limit at idle and still sees a lean reading on bank 1, it stores P2187.

Both references group the causes into two kinds: extra air getting in, or not enough fuel getting through.

Common symptoms

• Check engine light on
• Rough or irregular idle
• Hard starting
• A whistling sound from a vacuum leak in some cases

Common causes

The causes below are the ones commonly seen with P2187. The actual cause can vary by vehicle, engine and mileage, so treat this list as a starting point, not a diagnosis.

• A vacuum leak, such as a cracked hose or intake gasket
• Low fuel delivery, such as a weak fuel pump
• Faulty fuel injectors
• An exhaust leak near the upstream oxygen sensor (listed by RepairPal)
• A faulty sensor, such as the MAF sensor

What to check with a scanner

• Compare fuel trims at idle and at 2,500 rpm. Trims that are high at idle but improve with rpm point to a vacuum leak.
• Listen for hissing or whistling around the intake with the engine idling.
• Watch the MAF reading at idle for an unusually low value.
• Note companion codes such as P0171, P0174 or misfire codes.

How to read and clear P2187 with OBD Master Pro

1. Plug in your adapter. Connect a generic ELM327 (or ELM329) OBD2 adapter to the diagnostic port, usually under the dashboard on the driver's side. Bluetooth Classic, Bluetooth LE, Wi-Fi and USB OTG adapters are supported.
2. Switch the ignition on. Turn the key to ON or start the engine, depending on your car.
3. Connect in OBD Master Pro. Open the app, go to Connection and pick your adapter. Classic Bluetooth adapters connect from the Bluetooth tab, Bluetooth LE adapters from the BLE tab with no pairing needed. Use the generic OBD2 / EOBD profile or your car's brand profile.
4. Read the codes. Open the fault codes screen to see stored, pending and permanent codes. Confirm P2187 is listed and note any other codes, since they often explain the cause.
5. Check the details. Look at freeze frame data, Live data and, where your car supports it, Mode 06 test results (see the checks above).
6. Fix, then clear. After the repair, clear the codes to turn off the check engine light. Clearing also resets the emissions readiness monitors, so drive normally and check the readiness screen before any inspection. Permanent codes cannot be erased with a scan tool; they clear on their own once the car's self test passes.

Tip: you can also look up P2187 and other codes in the app's DTC search without connecting to a car. If your adapter will not connect, use Connection > Share connection log and email it to support. Many cheap ELM327 clones only handle basic engine OBD2, which is all you need for P2187.

When to see a mechanic

Get professional help if any of these apply:

• A smoke test is needed to find a leak
• Fuel pressure needs testing
• The engine stalls or misfires

If you are unsure, a qualified technician can confirm the cause with tests such as smoke testing, pressure testing or scope readings. Clearing a code does not repair the fault.

Related trouble codes

See all OBD2 trouble code guides

Related guides

Check engine light on: what to do · How to read an OBD2 code (P, B, C, U) · Stored, pending and permanent codes and freeze frame · OBD2 readiness monitors explained · OBD2 glossary · OBD2 by car brand