Erratic temp reading -1997 Dodge Ram 1500

salvagegirl

I have a 1997 dodge 1500 5.2. It started out dying when warmed up. I hooked it up to the scanner and the temp readings are erratic. Engine dies when it is at -20 thru -40, but scanner does not read at that. Changed the computer, and other parts mentioned on forum but still dying with erratic readings. Any ideas???

ray80

Does it have a gauge that shows temps jumping around? At -20 -40 temps? Have to wonder about weak coolant or possibly sticky t-stat

salvagegirl

Have the scanner hooked to it and it is reading erratic. The dash gauge is reading correct. We have temp sensor, throttle position sensor, and the ecm. All have not made a difference.

Mr_Shiftright

What's the needle on the gauge doing? Does it move up and down slowly, or very quickly? Between what temps does the gauge fluctuate?

thecardoc3

salvagegirl said:

I have a 1997 dodge 1500 5.2. It started out dying when warmed up.

The first question is when it dies, what are you losing? Spark? Fuel? Both? Or in this case maybe just the control of the fuel? There are many times that a vehicle symptom is occurring such as your truck dying out and during some testing, a problem such as the erratic temperature sensor signal is discovered. The real fun starts when you realize there is a difference between "A problem" and "The problem". To completely repair a vehicle you have to identify and solve not only "the problem", but the other issues that could result in a similar, or currently masked symptom. What that means is the coolant sensor signal while it is a problem at this point hasn't been proven to be the cause of the dying out.

salvagegirl said:

I hooked it up to the scanner and the temp readings are erratic. Engine dies when it is at -20 thru -40, but scanner does not read at that.

This is hard to follow and if I was going to investigate your truck I'd first try and get you to help make this a little clearer, but ultimately have to experience the symptom first hand. Going from the perspective that the coolant sensor signal in scan data is erratic but the dash gage is not, testing would first concentrate on the coolant sensor signal to the computer.

When the sensor is reporting a cold temperature you would measure a high voltage, when it is warm it would be a low voltage. The circuit uses a 5v reference signal that comes from the computer, passes through a resistor inside the computer and then goes out to the sensor. From there it goes through the sensor which will have a varying resistance depending on the temperature and then goes to ground back at the computer.

When you see -40 in scan data that means the circuit went open. When the circuit is open you will see 5v right up to the point that the circuit failed and then 0v after that. The ground side of the circuit (return) should be close to 0v when the circuit is operating normally. If that rises to 5v when the scan data is showing the signal to be erratic then it is the ground circuit that is failing.

salvagegirl said:

Changed the computer, and other parts mentioned on forum but still dying with erratic readings. Any ideas???

Any Ideas?
Sure. Test, don't guess, each and every time no matter how obvious or simple a problem appears to be. I've seen countless repair attempts and advice given that try to suggest knowing how to diagnose and fix a car equals knowing what part to replace based on nothing other than what a given symptom is.

To test a circuit correctly you have to know how it works as well as how it could possibly fail. I've given that to you above, now you have to perform the tests that prove exactly what is happening and by doing that you will solve that problem.