Diagnostic Code 4238

Wanted to share in case this helps someone out in the future:

2018 Max with a 400

I got this code on first startup this year (on the hose) and returned again when I put it in the water, I tried running it at higher rpm under load to clean off the o2 but it still came back.

4238: Closed-loop gasoline bank2 high

https://uploads.tapatalk-cdn.com/202...7e03973ac6.jpg


I did some research and this points to the pre-catalytic converter oxygen sensor on the starboard side of the engine. In my research I found a lot of posts about exhaust leaks, cracked manifolds, y-pipe alignment, etc. Since the boat is already on the lift an hour or so from my house I went ahead and cross referenced the indmar part number and bought a o2 sensor from autozone for $75 (around 1/2 the price of most marine suppliers). Bosch 17321. I typically don’t like throwing parts at something before doing the proper diagnostics, if I had more time I would have switched the bank1 and bank2 sensor and seen if the problem followed that particular o2 sensor.

Anyway, I drove up today and put it in, no more code! Fingers crossed it stays that way, if not I’ll post back up.

Awesome and thanks for sharing. I've read of these O2 bank2 threads and posts. Some say drive them hard after filling up with ballast or surfing for a while and others say its from old gas. Who knows the culprit but thanks for sharing your cross reference part!

Quote:

---

Originally Posted by haknslash

Awesome and thanks for sharing. I've read of these O2 bank2 threads and posts. Some say drive them hard after filling up with ballast or surfing for a while and others say its from old gas. Who knows the culprit but thanks for sharing your cross reference part!

---

Yessir, if it had turned out to be more than $75 fix I would have called the dealer and let them handle it under warranty.

Quote:

---

Originally Posted by z28ke

Yessir, if it had turned out to be more than $75 fix I would have called the dealer and let them handle it under warranty.

---

Could you take a picture of where the sensor is located. I replaced two o2 sensors but I think I replaced the wrong two. I believe I replaced the post cat sensors and with the 4238 FMI O code I should have replaced the pre cat. Not sure which side so I may replace both. I am out of state and not near my boat unfortunately but want to have the right part this time when I return. Kids will want to get out to surf I am sure. Please let me know your thoughts.


Sent from my iPhone using Tapatalk

Quote:

---

Originally Posted by Wdavid

Could you take a picture of where the sensor is located. I replaced two o2 sensors but I think I replaced the wrong two. I believe I replaced the post cat sensors and with the 4238 FMI O code I should have replaced the pre cat. Not sure which side so I may replace both. I am out of state and not near my boat unfortunately but want to have the right part this time when I return. Kids will want to get out to surf I am sure. Please let me know your thoughts.


Sent from my iPhone using Tapatalk

---

Quote:

---

Originally Posted by Wdavid

Could you take a picture of where the sensor is located. I replaced two o2 sensors but I think I replaced the wrong two. I believe I replaced the post cat sensors and with the 4238 FMI O code I should have replaced the pre cat. Not sure which side so I may replace both. I am out of state and not near my boat unfortunately but want to have the right part this time when I return. Kids will want to get out to surf I am sure. Please let me know your thoughts.


Sent from my iPhone using Tapatalk

---

I circled the precat oxygen sensor in red, it has the blue wiring harness coming from it:

Trying to get pic to post

Here’s the pic:

https://uploads.tapatalk-cdn.com/202...56b8b366ea.jpg

Quote:

---

Originally Posted by z28ke

Here’s the pic:

https://uploads.tapatalk-cdn.com/202...56b8b366ea.jpg

---

Thank you. That is not the one I replaced. I replaced the post cat sensors. Bummer.


Sent from my iPhone using Tapatalk

Quote:

---

Originally Posted by Wdavid

Thank you. That is not the one I replaced. I replaced the post cat sensors. Bummer.


Sent from my iPhone using Tapatalk

---

Could you (or anyone here) provide a rough ballpark area of the post cat 02 sensors? Also trying to understand which side of the engine is bank 3.

I'd like to switch 02 sensors (banks 3 & 4) to trouble shoot an "EGO3 open / lazy" code that's recently surfaced on our 2017 Mondo (400 engine).

Lastly- do I need any fancy 02 sensor sockets, or will a 3/8" box wrench do the trick?

Any insight here would be greatly appreciated. Thank you.

Attachment 30519

The post cat sensors are after the cylinder chambers but before the blue silicone boots I'm the engine photo. Usually bank 1 and bank 3 are starboard side and bank 2 and 4 are port side 1&2 pre cat 3&4 post cat.

The wrench will be 11/16th, 17mm, or similar. Follow the wires to the sensors they have a blue sleeve over the wires to the sensors.

Quote:

---

Originally Posted by Holdmybeer

The post cat sensors are after the cylinder chambers but before the blue silicone boots I'm the engine photo. Usually bank 1 and bank 3 are starboard side and bank 2 and 4 are port side 1&2 pre cat 3&4 post cat.

The wrench will be 11/16th, 17mm, or similar. Follow the wires to the sensors they have a blue sleeve over the wires to the sensors.

---

Awesome, this is exactly what I needed. I believe I can see the post post cat 02 sensor in the engine photo (port side), that you're referencing. Also appreciate the bank info, seems to make sense. Heading up to the lake today, planning on tackling this when we get there. Thank you!