Bypassing/ignoring low coolant pressure sensor guardian mode?

Jmangus22

Member
Jul 1, 2020
69
Boat Info
Boatless
Engines
boatless
Looks like I have a coolant/water pressure sensor that has failed and is reading 0 psi at all times.

For some reason this doesn't cause any problems under 1200 rpms.. but above it the engine goes into guardian mode and wont run at high rpm.

The water TEMP is a steady 145 - 160 and it's a freshwater cooled engine..

The problem is the repair place it needs to go to today or tomorrow is a MUCH LONGER trip at 1100 rpm vs 4000.

Is there any way to tell the computer to ignore this sensor? I imagine this isn't the kind of sensor you can just unplug... because it NEEDS to get some kind of pressure reading..

It's on a 383 stroker FWC mercruiser motor.. thank you for any help!
 
As Scoflaw stated, sensor replacement is easy and fairly cheap fix if you now what you are doing.

I would think a resister in there that resembles the operating resistance of that sender could fake out the ECM.

Those sensors work on a 5 volt ref signal, through resistance, then to ground in ECM. ECM then reads the minute current / ref voltage through circuit.

I personally wouldn't do it because of risk of doing it wrong and trashing an ECU.

Quick video on replacing the sensor
 
Buy a new sensor, common failure and easy to replace.
That would be the easy way.. the problem is I'm on an island and parts will take a while.. was hoping to bring it to the painting place today. If not tomorrow will have to suffice. Looking at car parts as a temp solution now.
 
As Scoflaw stated, sensor replacement is easy and fairly cheap fix if you now what you are doing.

Looks like the normal reading for the coolant temp sensor @ 160 deg F is 450 ohms and at 100 deg is 1800 ohms. I would think a resistor close to the 450 ohms, or slightly higher, would fake out the ECM to thinking it was operating normally.

Those sensors work on a 5 volt ref signal, through resistance, then to ground in ECM. ECM then reads the minute current / ref voltage through circuit.

I personally wouldn't do it because of risk of doing it wrong and trashing an ECU.
Not a fix, but an "emergency work around to get me home or repair facility" work around.
Temp sensor is fine. Need the pressure sensor..
 
If you can get a hold of a potentiometer that is around 1-2k ohms connect it across the 5v and sensor terminals on the plug. Adjust to show around 5 psi on the engine.
 
If I just unplug it, will it give the beep every 2 mins? I saw a post that someone had to do that when they were 25 miles out to sea.. That would be fine... the part that isn't fine is 1200 rpms and blaring constant beep.. might just have to try that..
 
One other weird data point. The code is not thrown when in N - it will run at 2k rpms as normal with no code thrown.. but the moment you try and do it in gear it throws it.

Neutral position sensor and drive oil lube level sensor can be disconnected and the same thing happens.

The coolant pressure sensor shows zero psi in Vessel view, which is why I'm focused on that one. Why would it make a difference if it was in N or FWD ?
 
As Scoflaw stated, sensor replacement is easy and fairly cheap fix if you now what you are doing.

I would think a resister in there that resembles the operating resistance of that sender could fake out the ECM.

Those sensors work on a 5 volt ref signal, through resistance, then to ground in ECM. ECM then reads the minute current / ref voltage through circuit.

I personally wouldn't do it because of risk of doing it wrong and trashing an ECU.

Quick video on replacing the sensor
Thank you for your post and the video. Saved the day.. dropped it into a cup of salt terminator x and 10 mins later we had a working boat!!

Going to order the correct part and move on.. super quick save though and much appreciated!!
 
If you can get a hold of a potentiometer that is around 1-2k ohms connect it across the 5v and sensor terminals on the plug. Adjust to show around 5 psi on the engine.
It is a 3 wire sensor, so I would be very careful on how it's being done.
 
Thank you for your post and the video. Saved the day.. dropped it into a cup of salt terminator x and 10 mins later we had a working boat!!

Going to order the correct part and move on.. super quick save though and much appreciated!!

Outstanding....
 

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