A leaking or stuck-open fuel injector on bank 2, delivering excess fuel into the cylinder.; A faulty pre-catalyst oxygen sensor on bank 2, sending a false rich signal to the computer.; A stuck-open or leaking evaporative emissions purge valve, allowing fuel vapor to be drawn into the intake manifold.; High fuel pressure caused by a failing fuel pressure regulator or a restricted fuel return line.; A dirty or failing mass air flow sensor that is over-reporting airflow, leading the computer to add too much fuel.; An intake air leak after the mass air flow sensor, which can cause unmetered air to enter and disrupt fuel trim, though this more commonly causes a lean condition.; A faulty engine coolant temperature sensor that is stuck reading cold, causing the computer to enrich the mixture excessively.

DTC codes / BMW codes / P1093

P1093 · BMWPre-Catalyst Fuel Trim Too Rich Bank 2

Q: What does code P1093 mean?

Pre-Catalyst Fuel Trim Too Rich Bank 2. P1093 on a BMW means the engine computer has detected a fuel mixture that is too rich on bank 2, which is the side of the engine that does not contain cylinder 1, as measured by the pre-catalyst oxygen sensor. The computer calculates fuel trim based on that sensor's signal and has reached a correction limit, indicating more fuel is being delivered than can be burned efficiently.

P1093 on a BMW means the engine computer has detected a fuel mixture that is too rich on bank 2, which is the side of the engine that does not contain cylinder 1, as measured by the pre-catalyst oxygen sensor. The computer calculates fuel trim based on that sensor's signal and has reached a correction limit, indicating more fuel is being delivered than can be burned efficiently.

SystemPowertrain

Code typeBMW specific

SeverityMedium

Fix difficultyProfessional

AreaFuel and air metering and auxiliary emission controls

Symptoms you may notice

Often no symptoms besides the warning light, especially if the rich condition is mild or intermittent.
A noticeable drop in fuel economy, as the engine is consuming more fuel than necessary.
A strong gasoline odor from the exhaust, particularly at idle or after a cold start.
Rough idling or engine stumbling, especially when the mixture is excessively rich.
Black, sooty exhaust smoke or black deposits on the tailpipe.
In some cases, a hesitation or stumble during acceleration if the rich condition causes fouled spark plugs.

Common causes, most likely first

A leaking or stuck-open fuel injector on bank 2, delivering excess fuel into the cylinder.
A faulty pre-catalyst oxygen sensor on bank 2, sending a false rich signal to the computer.
A stuck-open or leaking evaporative emissions purge valve, allowing fuel vapor to be drawn into the intake manifold.
High fuel pressure caused by a failing fuel pressure regulator or a restricted fuel return line.
A dirty or failing mass air flow sensor that is over-reporting airflow, leading the computer to add too much fuel.
An intake air leak after the mass air flow sensor, which can cause unmetered air to enter and disrupt fuel trim, though this more commonly causes a lean condition.
A faulty engine coolant temperature sensor that is stuck reading cold, causing the computer to enrich the mixture excessively.

How to diagnose and fix it

Connect a scan tool and check for any stored or pending codes, then record freeze-frame data to see the conditions when P1093 set.
Inspect the pre-catalyst oxygen sensor on bank 2 for contamination or damage, and compare its live readings with the bank 1 sensor to verify the rich signal.
Perform a fuel injector balance test or listen to each injector on bank 2 with a stethoscope to identify a leaking or stuck-open injector.
Check the evaporative emissions purge valve for proper operation; it should hold vacuum when closed and not allow fuel vapor to pass continuously.
Measure fuel pressure with a gauge and compare it to the manufacturer's specification to rule out high fuel pressure.
Clean or replace the mass air flow sensor if its readings are inconsistent with actual airflow, and check for intake leaks after the sensor.
Verify the engine coolant temperature sensor readings against actual engine temperature with an infrared thermometer or scan tool live data.

Before you replace the bank 2 oxygen sensor

A rich condition on bank 2 can be caused by a leaking injector that does not always trigger a misfire code, so injector balance testing is often more revealing than simply replacing the oxygen sensor.
The pre-catalyst oxygen sensor may be reporting accurately; a false rich signal from a contaminated sensor is less common than an actual rich mixture, so verify with fuel trim and injector tests before condemning the sensor.
A stuck-open evaporative purge valve can cause a rich condition that is worse at idle and after refueling, and it often sets P1093 without any other codes, making it a commonly overlooked cause.
On BMW engines, a failing high-pressure fuel pump on direct-injection models can cause rich running on one bank, but this typically sets additional codes; always check for related fuel pressure codes before assuming a simple injector issue.
Bank 2 is the side of the engine opposite cylinder 1, so on inline-six engines it is the rear cylinders; misidentifying the bank can lead to replacing the wrong sensor or injector.

Can I keep driving with P1093?

You can usually drive the car with P1093 set, but avoid hard acceleration and long trips until it is diagnosed, because a rich mixture can foul spark plugs and damage the catalytic converter over time. If the engine runs rough, smells strongly of fuel, or the check engine light starts flashing, stop driving and have it inspected immediately.

Tools that help

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