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.
Medium severity. Can I keep driving?You can drive in moderation, even if you notice the engine running rough when stopped. Get it checked soon, because if the leak is in the brake booster hose the pedal can become harder: in that case, do not keep driving.
Bank 1 is the side of the engine with cylinder 1. Inline engines only have this bank.
Symptoms
- Malfunction indicator lamp on
- Rough or hunting idle, hissing from the engine bay
Most likely causes
- Air leak after the air mass sensor, often at the crankcase ventilation
- Damaged front oxygen or A/F sensor wiring
- Fuel pressure too low
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: medium
- It affects emissions.
What each character of P2187 means
- P: Powertrain: engine and transmission
- 2: Generic code: same on every make
- 1: Air and fuel
- 87: Specific fault in that system
Frequently asked questions
Can I keep driving with code P2187?
You can drive in moderation, even if you notice the engine running rough when stopped. Get it checked soon, because if the leak is in the brake booster hose the pedal can become harder: in that case, do not keep driving.
What causes code P2187?
The most common causes are: air leak after the air mass sensor, often at the crankcase ventilation; damaged front oxygen or A/F sensor wiring; fuel pressure too low.
Related codes
- P2189System Too Lean at Idle (Bank 2)
- P2177System Too Lean Off Idle (Bank 1)
- P0171System Too Lean Bank 1
- P2279Intake Air System Leak (Bank 1)
- P2188System Too Rich at Idle (Bank 1)
Sources
- gsi.ext.gm.com: 08 GRP02 LLT Engine
- gsi.ext.gm.com: 2005file14
- saabwisonline.com: dtc p2177 or p2187
- static.nhtsa.gov: SB 10043872 9159
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.