water pressure sensor/oil warning buzzer

[michaelmeseck]

hey guys,

I have a 2005 yamaha 150 4 stroke with about 200 hours on it (square command link gauges). motor wouldn't start today after being anchored for awhile and was giving me Oil Pressure warning on gauge along with buzzer. then eventually just read Check Engine as I kept trying to restart. checked oil level and it was dead on between the high and low marks (recent oil change about 20 hours ago).

ended up pulling the water pressure sensor off off the motor (it has worked intermittently since I bought the boat last year) and motor started right up.

does it make sense that a bad water pressure sensor would not allow me to start the motor? and more importantly... is there any good reason that a bad "Water Pressure" sensor would cause the gauge on the dash to say that I have low "Oil Pressure" and sound the buzzer? (ps - no debris in motor, peeing strong, etc etc).

according to my boat's records this is the 3rd h2o sensor in 200 hours, so i'm considering just buying the plug for the sensor hole on the motor and doing without it. any advice on this would also be appreciated (i.e. do I need to remove the sensor from the ECM completely or just unplug from the motor...).

Thanks in advance for your help.

- Mike

[boscoe99]

Early water pressure sensors and water speed sensors are known to be problematic. The design has been changed and updated sensors are available.

The problem was that the sensor would fail in a manner that would allow water to get across the sensor and into the electrical side. Once that happened any number of strange and mysterious gremlins can occur.

Carefully inspect the electrical terminals in the sensor connector? Do you see signs of water and/or corrosion? Water has been known to migrate up the wiring all of the way to the ECU. Strange I know.

You might want to disconnect the connectors at the ECU and check the pins and sockets for any signs of distress.

Do you have the early version of sensor or the later version? It is possible that even if you have the later version it too might have failed.

[michaelmeseck]

thanks so much for the quick and thorough reply. according to the service records I have from the previous owner... the ECU assembly, wire harness assembly, fuse box assembly, and 3 sensors were replaced due to "water contamination" in 2010. I'm assuming they are the newer version but will check today to be sure. are these "sensors" also called "senders"?

the guide that gave me the tip about the sensors while I was stuck yesterday said that he spent over $1,000 replacing his oil pressure sensor 3 times before finally deciding to cap it off and go without it. do you know of any problems doing this with the water pressure sensor? I constantly check to make sure the motor is peeing anyway, so I feel like I could go without it, but I'm also not a mechanic. with it unplugged the motor seems to run absolutely fine. plug it back in and motor stops after about 10 seconds every time (this is at home with muffs on at idle).

thanks again for the reply. I'll let you know what I find.

- mike

[99yam40]

water contamination could also be caused by motor going under water, are you sure it was due to faulty sensors all of that was replaced?
Inspection for corrosion on connections would be a good idea

Does not make since to me the oil pressure alarm would be activated by faulty low water pressure sensor, but what do I know.
I am not sure any of the alarms would keep motor from starting anyway

[rodbolt17]

no alarms or sensors that will cause a shut off by design.

a failed water pressure or speed sensor can push water to the ECM.
I have heard it can push water all the way to the ign switch.
I have seen it as far as the 10 pin connector.
unplug the ECM connectors and inspect for corrosion.

[rodbolt17]

I see way to many switchs and sensors get replaced cause the computer said they were bad.

I know a lot of techs and owners that have spare switchs and sensors now.

those switchs and sensors can be tested for proper operation.

that ECU is rather stupid, it cant tell the difference between a short or open in the harness nor pin corrosion or did the switch/sensor fail.

on the command link at key on engine off you can push and hold the mode button about 16 seconds and it will display code numbers.
lowest first and it must be cleared to show the next code.

[rodbolt17]

also if your experiencing multiple sensor codes or "failures with the same sensor.
test the sensor reference voltage.
some ECU have 2 ref circuits,some only one.
many times multiple sensors share the same ref voltage circuit.
sometimes the sensor that failed and is loading down the ref voltage isn't the one the laptop highlights.

goes back to ECU mapping.

if a sensor that is designed using a 5V ref plus or minus .02V typically, is fed 4v then its output voltage may or may not throw a code but the ECM will react to the lowered feed back from that sensor.

the ECU may not realize the ref voltage is bad.

[michaelmeseck]

update

checked entire wiring harness (speedo, water, and oil sensors) back to the ECU. absolutely no sign of water or corrosion. all pins are bright, shiny and clean. the sensors are the newer versions. the back of my ECU has a mottled appearance that oddly enough looks like chunks of salt under a thin coat of rubber. is this normal? I will try to post a pic of this later from my computer.

I pulled the WPS and it was found to have a *tiny* bit of sand inside of it. I gently rinsed it (being sure to keep the electrical side dry), put it back in, attached wiring and it started right up. ran great for about 10-15 minutes on the muffs at home.

took it to the landing and it wouldn't start again. this time the dash gauge only said "check engine" (nothing about oil warnings). pulled the wire on the WPS and it started right up. ran around for about 3 hours at various speeds and no problems whatsoever. guess I'll pull it again tonight and check for more mud/sand? will also check for codes on the tach.

I flush this motor religiously with both the onboard attachment and then the muffs, so I'd be surprised if it's "full" of sand. that sensor has worked intermittently ever since I got the boat last year. is it possible for it to be break"ING" (seems like it would be an all or nothing thing - good or broken)?

thanks again to all for the advice. Andy at SIM... can you shoot me a quote for the water pressure sensor vs the plug to just cap it off (and let me know if there's any problem with just capping it?).

thanks!
- mike

[boscoe99]

The mottled look you are seeing is normal. Looks to me like large chunks of sand that have been coated with whatever it is they use to seal the unit.

You need to contact Andy either via his website or the other site that he hangs out at, and at which he has a forum.

It is perfectly normal to just cap off the pressure sensor connector. That is the way that it comes from the factory.

Sounds to me like a new sensor is in your future, if you still want water pressure displayed on your CL gauge. What you are describing is just one of many ways that a faulty pressure sensor can cause the motor to act up. If and when a dealer calls Yamaha US for support, with respect to a problem that is making no sense whatsoever to them, one of the first questions they will ask is if the motor has Command Link gauges and if so are the water pressure sensors installed.

[michaelmeseck]

thanks man. I'll hit up andy on THT forum. appreciate the help.

[rodbolt17]

quick way to tell which sensor you have is to simply look at it.
if the holder hex and the sensor hex are the same size its the wrong sensor.
if the sensor hex is considerably larger its the right one.
the old one has not been in production for 5 yrs or better.

odds are a new sensor is going to give the same results.
have a look at the ref voltage and monitor it.
like I said, most sensors/switchs I see replaced are not bad.

like I mentioned, most ECU's only have 1 ref voltage output,typically the orange sensor wire.

if ANY sensor loads down the ref line ALL sensors on that ref line now give bogus information to the ECU.

[michaelmeseck]

update

thanks Rodbolt17.

the WPS that is in there is definitely the newer version, but it's been in there for 3-4 years and is definitely causing the problem.

did some more troubleshooting last night. sensor plugged in still only starts and runs intermittently. unplug it and boat runs just fine. even when the boat DOES run with it's plugged in it doesn't give a reading on the CL gauge. I don't think the sensor has completely failed, but is on it's way out. no codes at the CL gauge even after plugging in sensor and forcing it to stop, and now rather than getting an oil pressure warning it simply says "check engine". I can see how these gremlins can be hard to track down. I'd check voltages but I don't have a multi meter handy and it seems pretty obvious that it's this sensor going bad.

a friend of mine recently went through 3 water pressure sensors (that were giving him oil pressure warnings) and finally decided to plug the port and cap off the wiring. I think I will do the same. last night I also removed the "connector" that the sensor screws into and there was a small amount of debris (salt/sand) inside the port. I ran the motor with a small hose coming off of this port for a few seconds to flush out that debris, but I'd imagine that wasn't helping the sensor at all...

mike

[boscoe99]

There is something to be said for simplicity in the form of a mechanical water pressure gauge.

Integration can be fine but it can create another set of issues altogether. Great when all the stuff works together but not so great when it does not.

And then there is the issue of software. Think about airplane engines that are con*****ed with software. The engineers will say that a software problem cannot shut an engine down. However, on one airplane with which I am familiar the pilots were flying merrily along and the APU (aux power unit) started up on its on. Software bug. When the engineers were asked how can software start an engine without any pilot involvement but it cannot shut an engine down without pilot involvement they hemmed and hawed and look down at the ground and said it can't happen.

[boscoe99]

no alarms or sensors that will cause a shut off by design.

a failed water pressure or speed sensor can push water to the ECM.
I have heard it can push water all the way to the ign switch.
I have seen it as far as the 10 pin connector.
unplug the ECM connectors and inspect for corrosion.

In light of the OP's report that the motor will not start with the failed sensor connected are you going to reconsider your comment?

I suspect that only Mitsubishi knows all of the various failure modes and the effects that they can cause to the motor. Probability of anything adverse happening (motor not starting or running for example) is more than likely extremely low but it apparently can still happen.

[michaelmeseck]

I fully agree.

There is a very obvious cause and effect relationship here. The dealership that fixed my friend's boat said that this is certainly not something they see on a regular basis, but that mine is now the 3rd that they have heard about in the past year or so that behaves this way.

They said that they have literally changed their "protocol" when someone comes in reporting similar motor symptoms. They now run the basic systems check and then head straight for the water pressure, speedo, and oil sensors. They even admitted that they have chased their tails for years with these intermittent electrical problems and probably replaced multiple ECUs and wiring harnesses unnecessarily.