Honda 225 - O2 Sensor Alarm on Startup

One of my 225-AK3's started throwing a code-1 (retrieved via MIL/paperclip trick), which is bad O2 sensor. I put in a new sensor and it seems fixed. However, I'm curious to understand more about the behavior I was seeing and the cause.

The engine would throw the code about 5 minutes after starting up. Didn't matter if I was just idling or was on plane and rolling along - seemed to be thrown based on a time-since-start. Stopping the engine after the alarm and restarting it - would cause it not to alarm again for the rest of the day. Even after a few hours at dock it would startup again fine and not throw the code. After a few days sitting, it would throw again on startup.

Wondering what would cause the behavior? Maybe the o2 heater circuit was going bad and at some point on restart there is enough engine heat once running to get a good sensor voltage? I was expecting a failed o2 sensor would throw codes more consistently on every start or periodically while underway.

Lots of great code-1 threads here that end in "put in a new sensor and it worked", but haven't seen many that detail the root cause.

After the boat sitting for four months due to dock replacement and surgery I finally was ready to put it back on the lift, went through my check list Racor, batteries, oil level, etc. and the last thing was to start it with the muffs on. What was strange I noticed steam coming from the exhaust for about 90 seconds then stopped. Found this to be strange because I only use Rec90. Anyway the next time I went to use the boat the alarm went off as you described. O2 sensor has since been replaced under warranty and like you the computer confirmed O2 sensor. I'll be curious how the discussion of "root cause" goes.

I have had a lot of problems with my twin 2008 bf200's. Not sure i can answerer the why? question but i have had the boat two seasons and had to replace both 02 units the first season and now i am battling with my port motor again same #1 alarm. My motors have the upgraded 02 sensors installed and ecu flashed appropriately. I bench test the "Failed" sensor and they produce the correct voltage .989DCV and the heater circuit measures correctly on the resistance. i have had success cleaning the sensor in muriatic acid and carb cleaner and lasting maybe 60 hrs until it alarms again. If water hits them when they are warm it seems to ruin them. i think the ecm is entirely to sensitive to the feedback from the sensors. I am running the walker/ngk units #932-24008 about $110 a pop.

brettmarl said:

One of my 225-AK3's started throwing a code-1 (retrieved via MIL/paperclip trick), which is bad O2 sensor. I put in a new sensor and it seems fixed. However, I'm curious to understand more about the behavior I was seeing and the cause.

The engine would throw the code about 5 minutes after starting up. Didn't matter if I was just idling or was on plane and rolling along - seemed to be thrown based on a time-since-start. Stopping the engine after the alarm and restarting it - would cause it not to alarm again for the rest of the day. Even after a few hours at dock it would startup again fine and not throw the code. After a few days sitting, it would throw again on startup.

Wondering what would cause the behavior? Maybe the o2 heater circuit was going bad and at some point on restart there is enough engine heat once running to get a good sensor voltage? I was expecting a failed o2 sensor would throw codes more consistently on every start or periodically while underway.

Lots of great code-1 threads here that end in "put in a new sensor and it worked", but haven't seen many that detail the root cause.

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My '04 225hp did the EXACT same thing as yours, next time this happens I'll just start run and re start to keep the o2 sensor happy, those things are expensive to be constantly replacing them.

Well, I don't have a good answer to any of this - just some observations. When Honda went with the new-design HO2 sensors (14 mm base) it seems like they got it wrong. These newer sensors have a much higher failure rate than the old (22 mm base) design, based on the posts on this forum over the last 15 years. Indeed, my 2007 BF 225 (having g the original design HO2 sensor) with over 2200 hours is still running on the original sensor. I test it every 100 hours during scheduled maintenance by shunting the service connector.

You also need to keep in mind that a misfiring spark plug or a failing coil will also throw a code "1" as will fuel pressure that is out of spec. The Helm shop manual doesn't say this directly, but the procedure for troubleshooting a code "1" says to test the fuel pressure, implying that fuel pressure out of spec can trigger a code "1."

My suspicion is that the newer ECU's that are supposed to be paired with the newer sensors are entirely too sensitive to the HO2 signal it is receiving. That is, the normal operating range parameter is programmed too narrowly. As the sensor gets some hours on it (perhaps the heating element is not getting to temperature soon enough or the zirconium dioxide is degrading), the signal fluctuates more and the ECU throws a code "1." That explains why a lot of folks get the alarm, turn off their engine, and after re-start do not get another alarm during that run.

Given that the HO2 sensor signals the air-fuel ratio to the ECU which adjusts injection fuel quantity to achieve the stoichiometric (optimum proportion of) air-fuel ratio. Then an alternative way to tell if the HO2 is really malfunctioning is to inspect the spark plugs for signs of black soot, indicating that the ECU is not giving the optimum fuel mixture to the injectors.

As an aside, it you have access to the Helm shop manual and really want to know how this engine and the sensors operate, read Chapter 18. I had the manual for over 5 years before I did that. It should have been the first chapter I read.

Great info!

Brand new sensor and still intermittent alarm #1 mostly at idle speed. I got on plane it went into alarm went to limp mode and cleared itself before I dropped off plane I have twins. getting pretty old. Should i just remove the reducers in the manifolds and have both motor's flashed to work with the old 22mm sensors? Honda really Screwed this up.

chawk_man said:

Well, I don't have a good answer to any of this - just some observations.
As an aside, it you have access to the Helm shop manual and really want to know how this engine and the sensors operate, read Chapter 18. I had the manual for over 5 years before I did that. It should have been the first chapter I read.

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fantastic answer. thanks. i'm going to pull out my shop manual next time i'm at the boat and read that chapter. admittedly i've only used the shop manual to try and follow procedure for maintenance items at this point and haven't spent anytime trying to learn how the engine works. hopefully i can wrap my head around it

O2 sensor fault does not cause engine to go into limp mode, only oil pressure failure or overheat, neither of these conditions log a code, so you're probably chasing the wrong fault. ECM cannot be reflashed either

Interesting it keeps throwing the #1 code every time and i clear it and it comes back again. I just ordered the doctor h so hopefully i can get to the bottom of this soon. Otherwise the motor runs flawlessly and smooth all the way up to 5600rpm no issues.

Ian - I think we were answering two different posts.

I was replying to the original post from bretmarl. He didn't mention going into LIMP mode.

I think you were replying to the post from Kstafford who stated his engine did. But I question that because he said that it cleared itself before dropping off plane. With dual engines, I think it might be difficult to tell.

Correct I did jump into the middle of the OP,s thread. I replaced my 02 on the port motor which solved the problem for at least a hours worth of runtime at all speed ranges.
Then i went up on plane and around 3800 rpm it alarmed i felt immediate power loss looked back and saw the motor shuddering a bit i assume from being dragged along still in gear and by the time i turned forward again the beep stopped and power came back on as normal...pretty weird i guess i will be hooking it to heal tech when it arrives to me on Saturday.

Kstafford said:

Correct I did jump into the middle of the OP,s thread. I replaced my 02 on the port motor which solved the problem for at least a hours worth of runtime at all speed ranges.
Then i went up on plane and around 3800 rpm it alarmed i felt immediate power loss looked back and saw the motor shuddering a bit i assume from being dragged along still in gear and by the time i turned forward again the beep stopped and power came back on as normal...pretty weird i guess i will be hooking it to heal tech when it arrives to me on Saturday.

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Hi,
I own a 2006 BF225 and using Heal Tech. Just replaced my O2 Sensor as I had error code 41. Clearing the error code and checking new the data, no error code with the new O2 sensor, but with the engine running, I see the "Heated Oxygen Sensor Control" going 'on' and 'off' repeatedly, every 1 to 5 secs. Have you seen this, is it normal?
Cheers