Hi I hope I'm in the right place. I have a 2002 Dodge Ram 2500 5.9 gas. I had a problem with my alternator and replaced it, then I replaced the battery. Now when I start the truck my check gauge light comes on and the temperature gauge will peg out at HOT even though the truck hasn't been driven. My husband pulled the code P0118 and it said something about the engine coolant sensor, so we replaced that. When he started the truck it was doing the same thing with the check gauge light coming on and the temperature gauge pegging out hot. Can someone please give me some suggestions, this truck is driving me crazy.

 

Yours is actually still a second gen. I'll move it there in a bit.

Temp gauge is told by the PCM what to display, so, if the gauge is pegging immediately, and you have already changed the sensor, then you have a wiring issue somewhere. Follow the wires back from sensor, see if they are shorted/pinched/otherwisemarfedup somewhere.

 

Thanks for the swift reply. To be honest we are getting on up in years and working on vehicles gets harder every day. Does the wire from the sensor run any where close to the alternator and maybe when we replaced it we damaged the wire, because that alternator replacement about killed us. But we will be checking that next. It only pegs when you start it and after running a few minutes it goes down to cool because it hasn't had time for the motor to heat up. But after you drive it awhile it goes to normal operating temperature and thank goodness it doesn't get hot. I'm just afraid that something will happen and I will break down in August in Texas.

 

Two wires on the sensor. And yeah, I think it does run near the alternator.....

 

My mind is as old as my body, I forgot to mention the temp. gauge only pegs out when the truck hasn't been driven like overnight. Once the truck is started it pegs out and then after running a few mins. it drops to the low side and then after you drive it slowly rises as the engine heats up, the it only goes to normal operating temperature. If I drive it to the store and when I come back out and the motor is still at least warm the gauge doesn't peg to the hot side. That is one reason I'm so lost on this truck.

 

Wonder if that is the normal behavior? Do you other gauges do the same thing. I think when you turn the key to start, the gauges should "test", and run their full sweep. (I don't think the speedo or tach do though......)

 

I really don't know if it's normal. I have never noticed it before if it has done it. Thanks for all your help.

 

Hop in the truck, and just turn the ignition on, see what the gauge does. (don't crank the engine.)

 

I don't know what my husband did, but he thinks he got it fixed. We will be able to tell in the morning because that is when it does it, on a cold start. I want to thank you very much for all your help.

 

I've just had a similar problem with my 2001 Ram 1500, 5.9. Two days ago I wrapped up my project of changing the valve cover gaskets. Next morning I tried starting it up and it took several tries and ran really rough and wanted to die, and would hardly idle at first, then after about 10 minutes of struggling it seemed fine but I noticed that not only was the "CHECK ENGINE" light on but also the "CHECK GUAGES" light was also on and the Temp. gauge was pegged at 260. The temp. gauge maxes out at 260 even if I just turn the key on without starting it. All the other gauges seem to be fine. Now after it finally was warmed up a bit it drove fine.
I'm sure I pulled on a wire too hard in the process of the valve cover gasket change. I checked the heat sensor behind the alternator and it looks like it's plugged in and fine, and yes I was able to push down on it to make sure it was plugged in.