P2179: System Too Lean Off Idle (Bank 2)
P2179 means the engine computer has added as much fuel as it is allowed to on bank 2 (the side of a V-type or similar engine that does not hold cylinder 1) while the engine is under load, and the mixture is still too lean, with too much air for the fuel. It turns on the check engine light and is not a stop-driving-now code, but it should be diagnosed soon because it affects emissions and can cause hesitation.
You can drive, but get it checked soon
The reference does not list limp mode for this code, so the car usually keeps running. A lean mixture under load can still cause hesitation and, if left alone, adds emissions problems, so have it checked soon and avoid hard acceleration or towing until it is.
What it means
The computer constantly adjusts fuel delivery using a long-term correction, which is a learned adjustment based on what the oxygen sensors report. P2179 sets when the part of that correction that applies off idle, as engine load rises, reaches its lean limit on bank 2. In other words, the computer is asking for more fuel and has run out of room to add it. The code applies to engines with a front oxygen sensor on each cylinder bank. If both banks run lean under load, the cause is probably something they share, such as fuel pressure, the fuel pump or the air mass sensor (which measures the air entering the engine). If only bank 2 is affected, the cause is on that side, such as a restricted injector, an intake leak at that bank's manifold or a front oxygen sensor reading lean. The light comes on after the fault is seen on two trips, and the code needs a drive cycle to confirm a repair.
Likely causes
- Low fuel pressure or air mass sensor fault, usually with P2177 tooPossible
Both are shared by the two banks, so a problem there tends to set the lean code on bank 1 (P2177) and bank 2 together.
- Restricted injector on bank 2Possible
A clogged injector delivers less fuel than the computer commands, so only the bank it sits on runs lean.
- Intake leak or front oxygen sensor fault on bank 2Possible
Extra air entering at that bank's manifold, or a front sensor that wrongly reads lean, pushes the correction to its limit on that side.
What you may notice
- Check engine light on after two trips
- Hesitation when accelerating or under load
What to check, cheapest first
- 1Read all stored codes and note whether P2177 (bank 1) is also present, since that points to a shared cause. · you can do it
- 2Look over the intake hoses and bank 2 manifold area for cracks, loose clamps or disconnected vacuum lines, and listen for a hissing sound with the engine running. · you can do it
- 3Check live data for the long-term fuel correction on both banks to see whether the lean condition is on one side or both. · mechanic
- 4Measure fuel pressure and compare it with the specification for the engine to rule out a weak pump or pressure problem. · mechanic
- 5Check the air mass sensor readings, and inspect the bank 2 front oxygen sensor for a lean reading that does not match actual conditions. · mechanic
- 6Test or clean the bank 2 injectors for restriction, then clear the code and complete a drive cycle to confirm the repair. · mechanic
Related codes
Frequently asked questions
Can I drive with P2179?+
Usually yes for a short time, since limp mode is not listed for this code. Expect possible hesitation under load, and get it diagnosed soon.
Can a gas cap cause P2179?+
The reference does not list the gas cap as a cause. The listed causes are fuel pressure, the air mass sensor, a bank 2 injector, an intake leak or a front oxygen sensor.
Will P2179 pass an emissions test?+
Probably not. The code is emissions-relevant and turns on the check engine light, which normally fails an inspection until it is fixed and the drive cycle is complete.
Can I fix P2179 myself?+
Some of it, such as checking for intake leaks. The repair is rated medium difficulty and estimated at 0.5 to 3.5 hours, depending on the cause.
Written with the help of AI from the public OBDex definition (CC0). Each make may use the code differently. Updated: 2026-11-10