[77newell]

The high voltage alarm on the coolant level; we are used to thinking of a level sensor as an on-off switch, on ecu engines it doesn't quite work that way. Voltage is applied through through a resistor in the ecu. The sensor has resistance such that it pulls the voltage down a bit under normal circumstances. If it is pulled down the right amount the ecu "knows" the system is electronically functional. With the high voltage alarm indication the ecu is saying the resistance in that sensor circuit, including the sensor itself, is higher than it should be. This means that the ecu cannot reliably determine whether the coolant level is safe. If the sensor circuit resistance is high, when the sensor resistance goes low when the coolant goes low, the ecu may not trigger the low coolant alarm and we end risking engine destruction. Therefore, the ecu system is designed to warn us that there is a problem with the circuit in addition to warning us when the coolant is low.

I'm not sure I have the details exactly right, but I am sure of the engineering approach used that verifies the integrity of all the sensor systems used by the ecu.

[qcj]

About a year ago Newell changed my coolant and the next morning when I pulled out to hook up the car my low coolant light came on.  I checked the sight glass in the tank above the radiator and it showed full.  The reservoir was a little low so filled it about half way and when I looked again the lights had gone off.  Came home with no problem.  About six months ago I turned the ignition on without c anking the engine in order to raise the coach to do some work under it and the lights came on again.  I check the sight glass and was full.  I then opened the tank slightly and coolant ran out.  Went back inside and lights were out.   This past week we took a trip to Kerrville, about 300 miles from Nacogdoches,  and all went great until it was time to leave.  The same thing happen.  The lights come on when you turn on the ignition for about 3 seconds then out, only this time as twice before they came back on.  Check engine, low coolant, cut off engine.  I back out and pulled around to hook up the car.  After about a minute they went off. Drove home with on problem.  This is the third time this has happen in the past year.
What i plan to do is what Richard suggested and that is to start with the coolant level sensor on the tank above the radiator.  I pulled a couple of my tail lights and can get to it pretty well, but can't tell whether it is a npt 1/4" or 3/8 without taking it out.  It would be nice to have one on hand when I do take it out.  I have already cleaned the terminals in the rear side engine compartment where there are 24 terminals and #15 on mine is coolant.  They were pretty nasty so I cleaned all 48 of them.  If anyone else has any suggestion I would like to hear them.  I know that Russ said the check the connection at the engine computer and that is on my list.

I have owned the coach for 5 years and never had this problem until the coolant was changed. Sort of strange.

[ccjohnson]

Chappell,
My new one is 1/4" . Old one was 3/8". I had to get a bushing to get new one to work. Might also be some sort of debris on coolant level sensor that is intermittent issue.

[qcj]

They come either size so I have found out. PN 23520380 or 23520381.  I guess the best way is to pull it.  

I never thought much about the problem until I read this post.  I do not want to get stuck out in the middle of nowhere and the problem does not go away.  Driving 50 MPH on 75 MPH highways would not be fun.  Why the problem leaves after a couple of minutes has got me concerned.

[NextNewell]

In my attempt to solve this issue, I started by cleaning all the connections, which did nothing. Having had this issue about two years ago (less than 3000 miles), I replaced the coolant level module which seemed to fix the problem.  This current issue is so similar to the last one that I wondered if the new module might have gone bad. Since I kept the old CLM, because I can't seem to throw anything out, I swapped it out with the installed CLM.  But even after trading them, nothing changing, so I made the assumption both CLM's were defective and got a new OEM CLM on eBay. 
The new CLM was delivered yesterday and I quickly installed it.  
Over the course of three engine starts, the check engine light came on but then off, then minutes later on, then off, then on/off, then on. The stop engine light came on twice, but at seemingly random times.  While it idled after the third start, the check engine light came on, then went off after which both lights stayed off. 
Even so, I don't trust that the issue is resolved.

[ccjohnson]

You may need to run new wire harness from CLM to DDEC. If that doesn't fix it, may need to get it into a good DD shop.

[Richard]

Is this sensor wired to ground on one side? Have you ensured that is a sound connection?

[RussWhite]

I have been down this road. And yes, it is grounded on one side. Easy to trace and, if memory serves, you will find it inside the stainless junction box accessible via the engine cover door. My problem, documented earlier in this thread, was at the ECM connector.

[Richard]

Russ,

I remembered you checking the ground, but I don't see that the OP has checked the ground.

[NextNewell]

Russ,

I remembered you checking the ground, but I don't see that the OP has checked the ground.

I checked the ground wire, but I will check it again, just in case.