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Adaptive lean bank 1 high (gas) - O2 sensors?


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Hi all,

I've recently started to see fault codes SPN 4237 FMI 0 pop up every now and then (maybe every 2/3 hours of wakesurfing).  I have an 2021 Axis 22 with about 200 hours in it.

After reading through some of the forum discussions, the most likely issue seems to be with carbon build up in O2 sensors. Has anyone seen issues with this, and what was the your solution? Cutting off power to reset the engine everytime this pops up is getting a bit annoying.  

Also is bank 1 referring to cats on starboard or port side?

cc - @csleaver thank you in advance :)

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SPN 4237 FMI 0 refers to the bank 1, pre-catalyst wide band oxygen (UEGO) sensor indicating that the engine is running lean (excess oxygen in the exhaust) and requires more fuel than what is allowed by adaptive correction.  The sensor is on the starboard side on a vdrive GM engine.

There is a service bulletin for 2021 Malibu Monsoon engines built from January to March that requires an ECM recalibration for emission controls.  Check with your dealer to see if your boat is affected.

The UEGO sensor can be swapped to the opposite exhaust bank to quickly determine if the sensor, or something else, is causing the problem.  If the fault code changes to SPN 4239 FMI 0 after swapping the sensor, then the sensor is likely faulty.  Otherwise, if SPN 4237 FMI 0 continues after the swap, then it is another issue.

These are some of the other possible causes: Oxygen Sensor Wiring open or short, Vacuum Leaks, Fuel Pressure too low, Exhaust Leaks, Fuel Quality changes, Poor System Grounding of the ECM harness to the battery cable.

Edited by csleaver
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2 hours ago, csleaver said:

SPN 4237 FMI 0 refers to the bank 1, pre-catalyst wide band oxygen (UEGO) sensor indicating that the engine is running lean (excess oxygen in the exhaust) and requires more fuel than what is allowed by adaptive correction.  The sensor is on the starboard side on a vdrive GM engine.

There is a service bulletin for 2021 Malibu Monsoon engines built from January to March that requires an ECM recalibration for emission controls.  Check with your dealer to see if your boat is affected.

The UEGO sensor can be swapped to the opposite exhaust bank to quickly determine if the sensor, or something else, is causing the problem.  If the fault code changes to SPN 4239 FMI 0 after swapping the sensor, then the sensor is likely faulty.  Otherwise, if SPN 4237 FMI 0 continues after the swap, then it is another issue.

These are some of the other possible causes: Oxygen Sensor Wiring open or short, Vacuum Leaks, Fuel Pressure too low, Exhaust Leaks, Fuel Quality changes, Poor System Grounding of the ECM harness to the battery cable.

Thank you for the swift reply. I'll try swapping out the sensors and see if there's a change in the fault code as you suggested

Regards to the O2 sensor location, i see that i have 2 per each side. When it's a "pre-catalyst", is it located more towards the bow side or aft side of the catalyst?

 

Best,
Charles

 

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The pre catalyst sensor 1 is closest to the front of the engine and the post catalyst sensor 2 is closest to the back of the engine.  Of course, the front of the engines faces the aft of the boat on vdrives.  The pre-cat wide band sensor has 6 wires and the post-cat narrow band sensor has 4 wires.

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