P2179
System Too Lean Off Idle Bank 2P2179 is a generic OBD-II powertrain diagnostic trouble code: System Too Lean Off Idle Bank 2. It is logged by the engine control unit when the scr/adblue monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P2179 means
DTC P2179 is the Bank 2 counterpart to P2177, indicating that the PCM has detected an excessively lean air-fuel mixture on the cylinder bank that does not contain cylinder #1 during part-throttle, off-idle operation. Bank 2 is only present on V-type, flat/boxer, or inline engines with separate oxygen sensor circuits for each bank. On an inline four-cylinder engine, which has only one bank, P2179 will not appear.
The PCM uses closed-loop fuel trim corrections to maintain stoichiometric combustion. When the correction commanded for Bank 2 at off-idle loads exceeds a programmed limit for a defined duration, P2179 is stored. A lean mixture means too much air relative to fuel is reaching the combustion chambers, which elevates combustion temperatures and can cause hesitation, misfires, or long-term engine wear if unresolved.
Because both banks share the same fuel system (same pump, same rail pressure), P2177 and P2179 appearing together strongly suggests a global fuel delivery issue — such as a weak fuel pump, low fuel pressure, or a clogged fuel filter — rather than a bank-specific problem. Conversely, P2179 in isolation usually points to a bank-specific vacuum leak on the Bank 2 side of the intake manifold, a Bank 2 exhaust leak near the upstream sensor, or a failing Bank 2 oxygen/air-fuel ratio sensor.
Diagnosis follows the same logical sequence as P2177: start with a fuel trim analysis, smoke-test the intake for vacuum leaks, verify fuel pressure, and evaluate sensor accuracy before inspecting injectors or considering PCM issues.
Common causes
Most-frequently reported root causes when P2179 is logged.
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1
Vacuum leak on the Bank 2 side of the intake manifold or associated hoses
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2
Failing upstream oxygen or air-fuel ratio sensor on Bank 2
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3
Exhaust leak near the Bank 2 upstream sensor causing false lean signal
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4
Contaminated or defective MAF sensor (affects both banks equally)
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5
Weak fuel pump or low fuel pressure (often triggers P2177 simultaneously)
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6
Clogged or stuck-closed fuel injector(s) on Bank 2
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7
Failing fuel pressure regulator
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8
EGR valve stuck open diluting intake charge
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9
Wiring fault or poor connection in Bank 2 oxygen sensor circuit
Symptoms drivers notice
How to diagnose P2179
A typical diagnostic flow when this code is present.
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1
Retrieve all codes and freeze-frame data; check whether P2177 is also present (both banks lean points toward a global fuel delivery problem rather than a bank-specific issue)
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2
Review Bank 2 long-term and short-term fuel trim values — large positive corrections confirm a lean condition; compare to Bank 1 to judge whether the problem is global or bank-specific
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3
Smoke-test or propane-enrich the Bank 2 side of the intake manifold and associated vacuum lines to find unmetered air ingestion
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4
Inspect for exhaust leaks upstream of the Bank 2 oxygen sensor, which can introduce oxygen and produce a false lean reading
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5
Test fuel pressure at idle and under load; a pressure drop under load with both P2177 and P2179 present indicates a failing fuel pump
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6
Check live O2/AFR sensor data for Bank 2 Sensor 1 — it should oscillate normally in closed loop; a lazy, stuck-lean, or non-responsive sensor needs replacement
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7
Perform a fuel injector balance or contribution test to identify any under-performing Bank 2 injectors
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8
Clear codes and road-test under the off-idle conditions captured in freeze-frame; re-scan to verify the repair
Related powertrain codes
- B0001 — PCM Discrete Input Speed Signal Error
- B0004 — PCM Discrete Input Speed Signal Not Present
- C0359 — Four Wheel Drive Low Range (4LO) Discrete Output Circuit
- C0362 — 4LO Discrete Output Circuit High
- P2000 — NOx Adsorber Efficiency Below Threshold Bank 1
- P2001 — NOx Adsorber Efficiency Below Threshold Bank 2
Frequently asked questions
What does 'Bank 2' mean, and which cylinders are affected?
Bank 2 is the cylinder group that does NOT contain cylinder #1. On a V6 or V8, one side of the engine is Bank 1 and the other is Bank 2.
If I have both P2177 and P2179, what does that mean?
Both banks running lean simultaneously strongly suggests a shared fuel delivery problem — most commonly a weak fuel pump, low fuel pressure, clogged fuel filter, or a MAF sensor that under-reports airflow.
Can an exhaust leak cause P2179 without a real lean condition?
Yes. An exhaust leak upstream of the Bank 2 oxygen sensor allows outside air to mix with exhaust gases, making the sensor read artificially lean.
Is P2179 more serious on a turbocharged engine?
Generally yes. Turbocharged engines are more sensitive to lean conditions because they operate at higher cylinder pressures and temperatures.
Disabling P2179 in software
RaceTune can permanently disable P2179 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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