Merc optimax 150 guardian mode at 2K

[Hefner413]

2012 150hp Mercury Optimax 2 stroke. Serial number 1B934227. The issue... we have a intermittent issue with the engine producing a constant beep and going into guardian mode around 2K rpm. I've been on the phone with mercury support multiple times and the boat is currently at the shop... but no resolution yet. The only ecu code is overspeed. I do understand what overspeed usually feels like (such as when engine trimmed too high etc), but this really does not seem to be the problem. And the problem does not occur every trip out. I can run 5K rpm without issue and speed up / slow down and everything runs fine. But it seems as though once the problem is triggered, it is constant for a few hours during which I cannot get above 2K without beep/guardian. The stream is steady and cool, so I do not think any issue with overheating. We considered that possibly the engine was mounted too high (which it does seem high) and possibly the prop cavitating, but the prior owner states that the engine has never been moved and the current prop is 3 years old. Of course the prior owner states that this was never an issue. Only things that I have done since purchase: replaced the fuel filter, replaced lower unit oil. The gas was likely old and was 3/4 full when I purchased. I put in 10 gallons of new fuel and added a can of sea foam. Another old thread with a similar issue mentioned a "trigger module" as a culprit or throttle position sensor issue. Any ideas? Thanks.

[lpugh]

Shift interrupt switch is bad or out of adjustment, Port side of the motor, 2 wires and is actuated by movement of the shift lever. Send a closed circuit signal to the the PCM, when a neutral position is indicated and the motor is revevd to 2k rpm it will alarm an go into guardian mode limiting the rpm

[Hefner413]

This is very helpful. Someone told me they had similar symptoms with the under cowl oil reservoir float separating from the magnet.

[JOE54]

Shift interrupt switch is bad or out of adjustment, Port side of the motor, 2 wires and is actuated by movement of the shift lever. Send a closed circuit signal to the the PCM, when a neutral position is indicated and the motor is revevd to 2k rpm it will alarm an go into guardian mode limiting the rpm

+1

[Hefner413]

Shift interrupt switch is bad or out of adjustment, Port side of the motor, 2 wires and is actuated by movement of the shift lever. Send a closed circuit signal to the the PCM, when a neutral position is indicated and the motor is revevd to 2k rpm it will alarm an go into guardian mode limiting the rpm

Is that the same as the TPS Throttle Position Sensor?

[JOE54]

no sir ,switch mounted on shift slide brckt, hard to see on a 150 with bottom cowls still on

[EuropeanAM]

Moved to correct forum.

[Hefner413]

Well, I finally got my boat back from the mechanic… unfortunately the mechanic had no answers for me other than stating he couldn’t recreate the problem and the computer only stated over-speed. Anyway… I took the boat back out and it soon was giving the warning tone and going into guardian mode with 2K limit. I then unplugged the sensor wire from the oil reservoir under the cowl. I then took off and when I hit 2K, it no longer went into guarding mode with a constant beep, but rather gave a 4 beep warning (low oil warning). I then plugged the wire back, planning to return to the shop to replace the oil reservoir. But thereafter, the warning tone / guardian mode would not initiate. I ran around the lake for over an hour without issue. So… maybe the wire to the oil reservoir sensor was not making good contact? And reconnecting it resolved the issue? I’m going back out on the lake all day tomorrow… fingers crossed that the issue is resolved. But if the warning tone restarts, then I’ll likely replace or repair the oil reservoir float/magnet.

Thanks for the help all.

[JOE54]

when you unplugged oil sensor you created another fault , if "computer "faults showed NEUTRAL OVER SPEED thats your problem /shift switch is bad or sticking you can unplug it and run it not causeing fault/guardian mode

[Hefner413]

when you unplugged oil sensor you created another fault , if "computer "faults showed NEUTRAL OVER SPEED thats your problem /shift switch is bad or sticking you can unplug it and run it not causing fault/guardian mode

Thanks. I asked the mechanic if it showed neutral during overspeed and he said no, it did not. So I'm thinking the overspeed code may have been a true code (we over-revved twice when taking turns tight). I am taking it back out today to see how things go. Fingers crossed.

[Hefner413]

when you unplugged oil sensor you created another fault , if "computer "faults showed NEUTRAL OVER SPEED thats your problem /shift switch is bad or sticking you can unplug it and run it not causeing fault/guardian mode

Well, tested today and I think your statement was correct…
I went out on the lake (with everything connected). I was going about 3K rpm and once again, solid tone / guardian mode with 2K limit. So I unplugged the oil reservoir sensor wire. At that point, I got the 4 beep every 2 mins as expected (so I unplugged the beeper, knowing that my oil level is fine), but shortly thereafter, it once again went into guardian mode / 2K limit. I returned to neutral and started going again and didn’t have guardian mode kick in again, but I’m back to square one. Would the shift interruptor switch cause guardian mode with 2K limit? And if the only code produced was over-speed (but not neutral overspeed)… would you still be suspicious of the shift interruptor switch?

[EuropeanAM]

Your engine was built around the time that the last of the Optimax calibrations were being written. NEUTRAL overspeed warnings and faults were being removed during that time (sometimes resulting in no fault, or simply an overspeed fault).

Follow what Joe recommended- unplug the Shift Position Switch (it is not an "interrupt" switch) and see if you can then accelerate normally. IF SO, replace the shift position switch, and have all of those faults that occurred (or were created) erased so as to not cause diagnostic headaches down the road.

[Hefner413]

Your engine was built around the time that the last of the Optimax calibrations were being written. NEUTRAL overspeed warnings and faults were being removed during that time (sometimes resulting in no fault, or simply an overspeed fault).

Follow what Joe recommended- unplug the Shift Position Switch (it is not an "interrupt" switch) and see if you can then accelerate normally. IF SO, replace the shift position switch, and have all of those faults that occurred (or were created) erased so as to not cause diagnostic headaches down the road.

Thanks so much. This is helpful. Definitely more info here than at my mechanic. Sorry for my lack of knowledge tho… I asked about the throttle position sensor (TPS) earlier and was told to look at the shift interruptor switch instead. Which am I looking for in this case?

[JOE54]

Thanks so much. This is helpful. Definitely more info here than at my mechanic. Sorry for my lack of knowledge tho… I asked about the throttle position sensor (TPS) earlier and was told to look at the shift interruptor switch instead. Which am I looking for in this case?

^^^^^^+50 have all faults cleared unplug connector to shift switch (youll have to pull lower cowling off on port side to find connector mandatory on 2.5 mtrs ) go run it = no guardian replace switch replug ///// ps; sometimes they just stick from grease and grime

[Hefner413]

^^^^^^+50 have all faults cleared unplug connector to shift switch (youll have to pull lower cowling off on port side to find connector mandatory on 2.5 mtrs ) go run it = no guardian replace switch replug ///// ps; sometimes they just stick from grease and grime

Thanks so much. Do you happen to know if I can clear faults on my own? And would the switch look something like this? MERCURY Genuine Neutral Switch - 8M0052939 <Read Forum Announcements>

[JOE54]

you cant without a cds or ddt , thats it

[EuropeanAM]

Yes, 8M0052939 is the type of switch that you would be looking for inside the cowling. Please take a moment to review the Forum Announcements: There are specific sites that we do not support here in the forums. Please keep that in mind.