M925A1 FailSafe Warning Buzzer when engine temp goes over 160 degrees

[mkupka]

I bought an M925A1 a few weeks ago through gov planet. The failsafe warning buzzer goes of when the engine temp goes over 160 degrees. scanning the manuals, the warning buzzer seems to only be mentioned for issues relating to the air system, but I did see a mention that FailSafe is for ALL systems in the vehicle, but specifically mentions only the lights when it talks about the systems other than the air system. I am thinking that it could be related to the thermostat not opening, or the fan not kicking in. Does anyone have any suggestions on where I should start looking? Thanks

 

[Suprman]

I believe originally the trucks had an overtemp light but it was eliminated early on. What do your air gauges read when the buzzer starts buzzing?

 

[mkupka]

Suprman, I have 110psi on primary and secondary. I tested the air sensors and they are both in spec. There was an engine temp light, but it has been painted over, so I removed the lens to see if the bulb was illuminated, but it was not. That lamp is probably no longer used, which I assume is why it was painted over.

 

[Suprman]

Most trucks don't have the light its blanked over. Maybe there's some system in place that triggers the alarm. First I woukd verify engine temp with an ir thermometer. When it's at 160 and buzzing, unplug the engine temp sender and see if the buzzing goes away.

 

[mkupka]

The only engine temp sending unit I found was the coolant temp, and unplugging it had no effect other than the temp gauge quit working. I will verify the engine temp with the IR thermometer when it arrives on Tuesday.

 

[mkupka]

I found the engine temperature sensor. I also noticed that the sensor wire has a new connector spliced onto it and taped with electrical tape. It looked suspicious, so I peeled back the tape and noticed some oxidation on the wires. now that could increase the resistance and cause the FWCM to think the engine is hotter than it really is. I will confirm the engine temperature tomorrow when the IR thermometer arrives, and resplice and solder the splice. BTW, disconnecting the engine temp sensor causes the FWCM to beep even when the engine is still cool, so I think I am on the right track.

 

[The HUlk]

a new connector spliced onto it and taped with electrical tape. It looked suspicious, so I peeled back the tape and noticed some oxidation on the wires. now that could increase the resistance and cause the FWCM to think the engine is hotter than it really is. I will confirm the engine temperature tomorrow when the IR thermometer arrives, and resplice and solder the splice.

Just the splice itself, without solder would increase the resistance. I'm surprised it worked for any length of time. Glad to see you have found the root of the problem.

I'm curious of which FSW module is in your truck? Could you describe it or photograph it?

 

[mkupka]

Hi Hulk, The FailSafe is: Cutler-Hammer Model SX7EA1 NO. 19207-11669142 MFD 8721 ( I assume it is 1987 )http://www.steelsoldiers.com/attachment.php?attachmentid=572658&stc=1&d=1438041165

 

[mkupka]

Well, after resplicing and soldering, it actually got worse ( now I get the buzzer at 140 degrees ), the oxidation is pretty far up the wire. I think I need to replace the whole wire.
Does anyone know a good source for the sensor plugs ( connectors ) I think I need to replace the wire lead for the Engine Temperature Sensor.

 

[The HUlk]

Well, after resplicing and soldering, it actually got worse ( now I get the buzzer at 140 degrees ), the oxidation is pretty far up the wire. I think I need to replace the whole wire.
Does anyone know a good source for the sensor plugs ( connectors ) I think I need to replace the wire lead for the Engine Temperature Sensor.

The engine temperature sensor is a N.C.(normally closed) switch which would apply GND to the FSW pin D through wire 35 when the temperature is not too high. After the temperature reaches the threshold(not sure what temp that is) the switch would open taking away the ground which would activate the buzzer and warning lamp(if equipped).

I would use a meter to measure the resistance from the temp sensor connector to pin D on the FSW connector. If the ohm reading is low, then I would say the temp sensor is faulty and opening at too low engine temp. Measure voltage from the temp switch output to +24VDC to confirm at what temperature the switch is opening.

This temp sensor and warning circuit/lamp was designed out in the A2 and modified out on many A1s, including mine. Reliability/accuracy issues probably played a role in why it was designed out.

 

[mkupka]

Hulk, you nailed it. I measured the resistance from the engine temp sensor to ground and watched it rise as the engine warmed up, then at about 130 degrees indicated on the coolant sensor, the resistance went infinite! So where can I buy the engine temp sensor? Can I go to a local diesel truck shop or is there a good source that Steel Soldiers members can recommend? Thanks so much!

 

[The HUlk]

Hulk, you nailed it. I measured the resistance from the engine temp sensor to ground and watched it rise as the engine warmed up, then at about 130 degrees indicated on the coolant sensor, the resistance went infinite! So where can I buy the engine temp sensor? Can I go to a local diesel truck shop or is there a good source that Steel Soldiers members can recommend? Thanks so much!

You can pay retail at places like this if it's available(there are several out there):
http://www.eriksmilitarysurplus.com/teseunwirush.html (this is the resistance type for gauge, not the NC switch type you are looking for)

Or post what you're looking for in the SS classified part wanted section.

Or just ground the sensor wire to modify it out like .gov did.