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DTC codes / Mazda codes / P1154

P1154 · MazdaBank 2 Fuel Control Shifted Rich FAOSC

P1154 on Mazda vehicles means the powertrain control module has detected that the bank 2 fuel control system has shifted rich, based on the Fuel Air Offset Short Correction (FAOSC) value moving beyond its calibrated limit. The engine computer is having to pull fuel away from bank 2 because the exhaust stream on that side is running richer than the computer commanded.

SystemPowertrain
Code typeMazda specific
SeverityMedium
Fix difficultyProfessional
AreaFuel and air metering

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms
  • A slight decrease in fuel economy as the engine runs richer on bank 2
  • A faint fuel odor from the exhaust or under the hood in more severe cases
  • Rough idle or uneven running if the rich condition becomes pronounced
  • Black or sooty exhaust tips on the bank 2 side of the engine
  • Occasional hesitation or stumble during acceleration when the correction reaches its limit

Common causes, most likely first

  1. A leaking or dripping fuel injector on bank 2, delivering more fuel than the computer commands
  2. A faulty or contaminated mass air flow sensor that misreports airflow and skews fuel trim rich
  3. A stuck-open or leaking evaporative emissions purge valve allowing fuel vapor into the intake
  4. High fuel pressure from a failing fuel pressure regulator or a restricted fuel return line
  5. A faulty oxygen sensor on bank 2 that falsely reports a lean condition, causing the computer to add fuel
  6. An exhaust leak upstream of the bank 2 oxygen sensor that draws in outside air and corrupts the reading
  7. A mechanical engine fault such as low compression or a worn camshaft lobe on bank 2 that alters combustion

How to diagnose and fix it

  1. Connect a scan tool and record all fuel trim values, then compare bank 1 and bank 2 short-term and long-term trims to confirm the rich shift is isolated to bank 2
  2. Inspect the bank 2 intake tract and vacuum lines for leaks or disconnected hoses that could affect that cylinder bank only
  3. Test the bank 2 oxygen sensor response with a scan tool or oscilloscope to rule out a lazy or biased sensor before condemning injectors
  4. Check fuel pressure with a gauge and verify it holds within specification after the pump shuts off, looking for a leaking injector or regulator
  5. Perform an injector balance test or remove the bank 2 injectors for flow testing and visual inspection for drips or fouling
  6. Smoke-test the intake and evaporative emissions system to find any unmetered fuel vapor source feeding bank 2
  7. After repairs, clear the adaptive fuel memory and road-test the vehicle to confirm the FAOSC value returns to its normal range

Why bank 2 runs rich on Mazdas

  • A leaking evaporative purge valve is one of the most commonly missed causes because it feeds fuel vapor into the intake and affects both banks, but the bank 2 trim often crosses the threshold first.
  • Technicians frequently replace the bank 2 oxygen sensor when the real fault is a dripping injector, so always verify injector balance before condemning the sensor.
  • An exhaust leak just ahead of the bank 2 oxygen sensor pulls in fresh air and makes the sensor report lean, which drives the computer to richen the mixture and sets this code.
  • Mazda's FAOSC value is an adaptive correction stored in the powertrain control module, so a battery disconnect or module reset will clear the code temporarily even though the mechanical fault remains.
  • A dirty mass air flow sensor can skew the calculated load and push fuel trim rich on one bank more than the other, so clean and verify the sensor before chasing injectors.

Can I keep driving with P1154?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy acceleration and long trips because the rich condition can foul spark plugs and damage the catalytic converter over time. If the check engine light begins flashing or the engine runs rough, stop driving and have it towed.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for Mazda vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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