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DTC codes / Chrysler codes / P1155

P1155 · ChryslerHO2S Lean Average Bank 2 Sensor 1

P1155 on Chrysler vehicles means the powertrain control module has detected a lean average fuel trim condition on Bank 2, which is the bank of cylinders that does not include cylinder number one, based on the upstream oxygen sensor signal. The computer has compared the long-term fuel trim average for that bank against its calibrated limit and found the engine is running too lean, meaning too much air or too little fuel is reaching those cylinders.

SystemPowertrain
Code typeChrysler 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 hesitation or stumble during acceleration, especially when the engine is cold
  • Rough idle quality that may feel like a mild misfire on one side of the engine
  • Reduced fuel economy as the computer adds extra fuel to compensate for the lean condition
  • In some cases, a faint sulfur or rotten egg smell from the exhaust if the lean condition overheats the catalytic converter
  • Occasional surging at steady cruise speeds as fuel trim corrections oscillate

Common causes, most likely first

  1. A vacuum leak on the Bank 2 intake manifold, such as a cracked intake gasket, deteriorated vacuum hose, or leaking brake booster check valve
  2. A dirty or failing mass airflow sensor that under-reports airflow, causing the computer to deliver too little fuel to both banks but triggering the lean average on Bank 2 first
  3. A weak or clogged fuel injector on one or more Bank 2 cylinders, restricting fuel delivery
  4. Low fuel pressure from a failing fuel pump, clogged fuel filter, or restricted fuel line
  5. An exhaust leak upstream of the Bank 2 sensor 1 oxygen sensor, allowing outside air to be read as a false lean condition
  6. A contaminated or aging Bank 2 sensor 1 oxygen sensor that responds slowly or inaccurately
  7. A PCV valve or hose leak that affects Bank 2 more than Bank 1 due to intake runner design

How to diagnose and fix it

  1. Connect a scan tool and record freeze-frame data and long-term fuel trim values for both banks at idle and at 2500 RPM to confirm the lean average is isolated to Bank 2
  2. Perform a visual inspection of all intake and vacuum hoses on the Bank 2 side, including the intake manifold gasket area, using a smoke machine if available
  3. Check fuel pressure with a gauge and compare against the Chrysler specification for your engine, replacing the fuel filter if pressure is low
  4. Clean the mass airflow sensor with a dedicated cleaner and verify its reported airflow matches expected values at idle and wide-open throttle
  5. Test the Bank 2 sensor 1 oxygen sensor response with a scan tool by watching its voltage switch rich-to-lean; a lazy or stuck sensor should be replaced
  6. Perform an injector balance test or remove and flow-test the Bank 2 injectors to identify a restricted or clogged injector
  7. After repairs, clear the codes and drive the vehicle through a complete readiness cycle to confirm the lean average does not return

What most technicians miss on P1155

  • A lean average code on only one bank often points to a vacuum leak that is specific to that bank's intake runner or injector base gasket, not a global intake leak, so a smoke test focused on the Bank 2 side is more productive than a general engine bay inspection.
  • The mass airflow sensor can cause a lean average on Bank 2 alone if the intake plumbing has a leak after the sensor but closer to that bank, so check the air intake tube and resonator for cracks before condemning the sensor itself.
  • An exhaust leak at the Bank 2 exhaust manifold or downpipe can pull outside air past the upstream oxygen sensor and create a false lean reading, so listen for a ticking noise when cold and inspect the manifold gasket and studs.
  • Chrysler engines with variable valve timing can set a lean average on one bank if the cam phaser or oil control valve on that bank is sluggish, altering the effective intake pulse and confusing the oxygen sensor reading.
  • Do not replace the Bank 2 sensor 1 oxygen sensor based on this code alone; the sensor is usually reporting a real lean condition, and replacing it without fixing the root cause will let the code return within a few drive cycles.

Can I keep driving with P1155?

You can drive the vehicle short distances to a repair shop, but avoid heavy acceleration, towing, or sustained high-speed driving because a prolonged lean condition on Bank 2 can overheat the catalytic converter and damage the engine over time. If the check engine light begins flashing, stop driving immediately and have the vehicle towed.

Tools that help

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

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