Another low coolant light thread

[dhirocz]

...this thing is about to drive me nuts.

Over the last month I've been fighting this thing. I started getting low coolant alarms, coolant wasn't low. They would randomly come and go while driving.

I checked the old sensor and put in a new sensor from my KW dealer. It became less temperamental...but kept doing it. Module was old and jumper harness between the sensor and module was a little weathered and beat up so I replaced them too, with paccar stuff.

Now here we are again. Still doing it randomly! Now, I do have to put coolant in it occasionally, but not in large quantities. If I drive it nicely it doesn't use much, I haven't put any in for a couple of weeks now. I drive it mostly across town, two trips a day, 6 days a week.

When it does it, the light will stay on, even if it's key on engine off, cap removed. Sometimes it gives me a CEL with it, sometimes not...I'm thinking it might be wiring related and I need to do a resistance check between the sensor and the ECM. Anyone have a pinout?

[KennyChatmon]

How are the hoses and clamps. You may want to chck them. You may not notice any coolant leaks. But if you have bad hoses and clamps it will set that type of stuff off.

[dhirocz]

All are new and high end T-bolt style clamps. No external leaks I can find.

I can look in the sight glass (it's a metal overflow bottle) and see that's it's full while the alarm is going off.

[dhirocz]

So I did happen to run into a bit of interesting information... apparently the metal overflow tanks that t2000's and T7's use has a floating metal pellet that interacts with the level sensor. Apparently over time, this pellet gets hung up or stops floating, and starts causing alarms and you have to install a new bottle.

Tomorrow after the truck cools I'll be looking into this. Sounds like a rather odd design.

[dhirocz]

Grrr....
*DING*DING*DING*DING*DING*

...I swear I'm hearing this in my dreams now.

I replaced the pigtail to the sensor harness, which was in bad shape. No change.

I found a cut in the wiring and some corrosion so it was repaired. No change.

I drained the tank and looked around in it with a boroscope. I didn't see this floating pill...or anything else either. Just a big empty tank.

I'm wondering if this module they sent me doesn't match the resistance values of the sensor, or if the resistance values may be operating in a different range vs what the ECM expects to see...

It occasionally goes away, but so far, no definite fix...

[Chamberpains]

I'm bringing up a point we brought up in TPS sensor wiring. You may be to the point where you have to check and just replace the wire for your low coolant sensor circuit. From the sensor to wherever and all the way back to the ECM. It is probably a 5 volt circuit and if you have any breaks or any weak points in it or what I found with mine was the copper had changed colors and got darker inside the insulation you could not see this from any point on the wire itself I had to strip it off to see it. You may need to just cut and solder splice (do not use butt connectors, crimp style or solder brand they will intermittently malfunction on low voltage circuits especially 5 volt signal circuits) a whole new wire in. It's a pain in the ass to pull wiring out and run new but so is listening to that god-awful beep beep beep I'm sure.