Check engine alarm

[johnnyc]

Alarm stays on after startup with only check engine prompt on display. Mechanic cleared it with his computer but now it’s back. All fluid levels are good and no blockage in water strainer, any thoughts???

[Tafika II]

What engine model?

[Charlie-Bravo]

Not model specific but ……
Oil pressure low ? that would keep the alarm going, and on some set ups if the alternator isn’t charging it will set off an alarm, as in a broken belt. I am sure you would notice a broken belt, but the split charge relay or some other charging gadget may have failed.
Less likely would be overheat as you have only just started up, but if you have a temperature sensor it may have failed.

Check that the alternator is charging the batteries,  you should see increased voltage compared to when the engine is not running.
Disconnect (just for investigation & if you are inclined to fiddle with things) the oil pressure sender, although some like the wires ‘shorted’ to think they have oil pressure.
Disconnect the temp sensor if you have one, and see if it makes a difference, may also require shorting of the wires.
Shorting of wires may pop a fuse, …. but they are cheap and easy, if you know where they are.

It may also be a fault in the alarm circuit not realising that the engine has started.

Perhaps your mechanic has an electrical colleague, or a better idea than just over riding your boats brain, let’s hope it’s not a brain malfunction.

Maybe an owner of your model has had the same thing and will pop along soon with the easy fix.

Post the fix when you find it.

CB

[Zanshin]

We really do need additional information here, every engine and engine panel works differently. But the warning comes on too quickly for a water temperature, engine temperature, exhaust temperature or even a water flow type of error. The most common error on a freshly started engine would be low oil pressure as charlie-Bravo has suggested.

[bereboot]

Alternator not charging?
Does the alarm standaard on when you increase rpm?

[johnnyc]

All good suggestions, model #4JH57 year 2018, I’ll check RPM trick tomorrow and report back. Thanks.

[johnnyc]

Just started the engine again, alarm persists with increase in RPM’s, oil pressure is 57 and belt is tight. Will continue to troubleshoot until mechanic arrives.

[johnnyc]

Also, forgot to say 14.1 volts when engine is running.

[Zanshin]

It does seem like it might be a bad sensor, rather than an an actual fault. You have checked the oil level haven't you?

[johnnyc]

Yes, changed oil and all oil and fuel filters. Oil level OK.

[shenandoah]

This happen to us on our SO 440 and it turned out to be the bow thruster, not the engine at all. And nothing was wrong except a for a malfunctioning alarm. 

If a certified mechanic has checked the engine and everything appears to be fine, then it is most likely a faulty censor. 

[johnnyc]

Thanks Shenandoah, what was the fix on the bow thruster fault? My bow thruster is working fine, did yours AND still created the alarm?

[shenandoah]

We had to replace the censor. Yes, the thruster itself was working fine. 

For what it is worth. I have a friend who crews with me. He is a former Naval officer and he says it was almost always a faulty censor when an alarm went off on any of the ships on which he served. The censor is the most fragile part in the whole system. 

[wolferich]

In my case there was a systematic search for faulty sensors or other causes of a continuous alarm of my Yanmar 4JH5E and nothing was found. After the control panel was changed everything worked fine again. 

[johnnyc]

Just changed the control panel ($900) with no change except louder alarm and similar CHECK ENGINE prompt on the panel.  I just sourced and priced all the sensors for the 4JH57 including 3 pressure sensors, 2 temperature sensors and 1 sensor assembly for about $1,573.  I am tempted to purchase one sensor at a time starting with the cheaper ones and working my way to the more expensive ones.  Any thoughts would be helpful.

[Charlie-Bravo]

You will have to don your Sherlock hat and become a detective, finding a faulty sensor can only be achieved by elimination.

Isolation of one sensor with no change in alarm would seem to eliminate it from your enquiries , and on you go to the next. Temperature sensors are generally warm and dry and so less likely, although not impossible to fail.

Finding out the full list of potential suspects must be the first step, then just wading through the isolations.
Replacement is a plan, but if you replace with another faulty one, rare but possible, the investigation could go on for some time.

Do tell when you find the pesky offender.

CB

[shenandoah]

I do most work on the boat myself, but personally when it comes to the computerization of engines, I think it is time to call in the pro. It may end up being cheaper than buying replacements for perfectly good parts. They should be able to hook up their computer and tell you what is wrong. 

Alternatively, remove the alarm. We used engines for years without the assistance of computers. 

Just a thought. 

[Zanshin]

Oil pressure and temperature sensors live a harsh life and can die prematurely. I find it odd that the technician couldn't read a fault code from the panel. I'm lucky that I have an ODBII engine and can plug in a cable and get a clear-text error message.

If you can isolate the cables for those sensors, either at the panel or at the engine then you can measure the resistance with a cold engine and check it against the specifications. Then fire it up and measure the values. I would think it is the oil pressure sensor that is either normally high or low resistance and doesn't change after a couple of seconds. The temperature sensor would only trigger an immediate alarm if it were broken full-on or off. I wonder if an open circuit caused by a bad connection or broken wire on either of those sensors would have the same effect....

[johnnyc]

UPDATE:  I found all 5 sensors and methodically pulled each one then pushed the power button on the panel.  Each time the alarm refused to turn off.   I also noticed the fuel/water separator filter did not have a sensor connected to it, only a crimped connection where I assume the sensor previously lived.  Mechanic still has not shown up despite many texts ( a common problem ).  I guess next steps are to check resistance in the wiring to each sensor as per previous comments.   Is is suspicious that there is NO fuel/water separator filter sensor??

[johnnyc]

My mistake: fuel/water separator sensor IS installed under the actual separator. Can I simply disconnect the wire crimp to test sensor rather than unscrewing the sensor and draining the filter vessel ?

[Zanshin]

I think so, the sensor is an on/off type and I assume that it is normally open and only closes in the presence of water.

[Charlie-Bravo]

Your mechanic not turning up can be irritating, but it has prompted your own investigation and should lead to a little more knowledge of your boat, which is a good thing.

Your comment re the water sensor disconnect, I would agree with Zaphod

I take it that you have a clear fuel bowl and can see no water in the bottom of it? obvious I know, but the obvious often gets overlooked in the enthusiasm of the hunt.

CB

[johnnyc]

Update No. 2 - the final sensor I checked was the fuel/water separator filter.  Changed the filter a few weeks ago and filter casing and bottom sensor are opaque not allowing me to see if there is any water.  Engine starts fine and runs great so I assume there is little water in the system.  I cut one of the fuel/water separator sensor wires and alarm stays on again after power button is pushed.  So, I will wait for the mechanic to show up to see if he can diagnose the issue.  Thanks for all your suggestions and will report when I have more information.

[johnnyc]

Jul 28, 2023 14:01:00 GMT johnnyc said:

Alarm stays on after startup with only check engine prompt on display. Mechanic cleared it with his computer but now it’s back. All fluid levels are good and no blockage in water strainer, any thoughts???

Well I am back after a somewhat limited sailing season to report on the CHECK ENGINE ALARM mystery.  After local mechanic cleared the alarm, it returned as previously stated.  I had a YANMAR mechanic review the engine on his computer and he found an old (early spring 2023) alarm triggered by an inadequate engine ECU shutdown that escaped the other mechanics.  I had apparently turned off the blower after engine shutdown by turning the batteries off.  Well, this action did not allow the Electronic Control Unit to properly turn off and it threw a fault into the system that eluded a number of NON YANMAR mechanics.  Lesson learned: push engine stop button, then wait 10-15 seconds for the ECU to properly shutdown before you long press the POWER button.