A leaking or stuck-open fuel injector on bank 2 delivering excess fuel; High fuel pressure from a restricted fuel return line or a faulty fuel pressure regulator; A contaminated or aged upstream oxygen sensor on bank 2 that is skewed rich; A vacuum leak that the engine management misinterprets, or a faulty manifold absolute pressure sensor biasing the fuel calculation rich; A leaking evaporative emissions purge valve that allows fuel vapor to enter the intake continuously; Excessive fuel in the crankcase from a failed high-pressure fuel pump diaphragm on certain engines; A restricted air intake or dirty mass airflow sensor under-reporting airflow on that bank

DTC codes / Chrysler codes / P1156

P1156 · ChryslerHO2S Rich Average Bank 2 Sensor 1

Q: What does code P1156 mean?

HO2S Rich Average Bank 2 Sensor 1. P1156 on Chrysler vehicles means the powertrain control module has calculated that the upstream oxygen sensor on bank 2 is reporting a fuel mixture that is too rich on average over a defined monitoring period. The computer is not condemning the sensor itself; it is flagging that the average rich correction on that bank has exceeded the calibrated limit.

P1156 on Chrysler vehicles means the powertrain control module has calculated that the upstream oxygen sensor on bank 2 is reporting a fuel mixture that is too rich on average over a defined monitoring period. The computer is not condemning the sensor itself; it is flagging that the average rich correction on that bank has exceeded the calibrated limit.

SystemPowertrain

Code typeChrysler specific

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Illuminated check engine light, often with no other symptoms besides the warning light
Noticeable drop in fuel economy over time as the engine runs richer than commanded
Black sooty exhaust smoke or a strong fuel smell at idle and under load
Rough idle or hesitation on acceleration when the rich condition is severe
Elevated carbon monoxide readings if the vehicle is emissions tested
Occasional misfire codes or rough running if fouled spark plugs develop from the rich mixture

Common causes, most likely first

A leaking or stuck-open fuel injector on bank 2 delivering excess fuel
High fuel pressure from a restricted fuel return line or a faulty fuel pressure regulator
A contaminated or aged upstream oxygen sensor on bank 2 that is skewed rich
A vacuum leak that the engine management misinterprets, or a faulty manifold absolute pressure sensor biasing the fuel calculation rich
A leaking evaporative emissions purge valve that allows fuel vapor to enter the intake continuously
Excessive fuel in the crankcase from a failed high-pressure fuel pump diaphragm on certain engines
A restricted air intake or dirty mass airflow sensor under-reporting airflow on that bank

How to diagnose and fix it

Connect a scan tool and record freeze-frame data plus long-term fuel trim values for both banks to confirm the rich average is isolated to bank 2
Inspect the bank 2 upstream oxygen sensor signal with a graphing scan tool or oscilloscope to verify it is genuinely biased rich rather than lazy or contaminated
Check fuel pressure with a gauge and compare against specification, looking for a regulator or return-line restriction
Perform an injector balance test or pull bank 2 injectors for a visual spray-pattern and leak-down check
Smoke-test the intake and evaporative emissions system to rule out a purge valve stuck open or a vacuum leak that is skewing the mixture
Clean or replace the mass airflow sensor only after confirming its reported airflow is inconsistent with actual engine demand
Clear the code, road-test through a complete drive cycle, and recheck long-term fuel trim on bank 2 to confirm the repair

What the rich average really tells you

P1156 is an average-based code, so a single momentary rich spike will not set it; the fault must persist across the monitor window, which is why intermittent injector leaks are easy to miss on a short test drive.
Technicians often replace the bank 2 upstream oxygen sensor first, but a sensor that reads rich because the engine is genuinely rich will set the code again within a few drive cycles.
A stuck-open evaporative purge valve is one of the most commonly overlooked causes because it feeds fuel vapor into the intake at all times, skewing both banks but tripping the bank-specific average first.
Chrysler's fuel trim strategy on some engines cross-references bank 1 and bank 2, so a bank 1 fault can mask or mimic a bank 2 rich average depending on which monitor runs first.
A restricted air filter or a mass airflow sensor that under-reports airflow will drive fuel trim rich without any driveability complaint, so always compare reported airflow to engine displacement and rpm.

Can I keep driving with P1156?

You can usually drive the vehicle to a shop, but avoid heavy acceleration and long trips because the rich mixture can overheat and eventually damage the catalytic converter. If the check engine light starts flashing or the engine runs rough, stop driving and have it 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.