Bought this truck a few weeks ago and the temp guage hasn't worked since I got it. It moves a little when you turn the truck on and off but not even up to the 130 mark. I did the cluster check function and the needle moves just fine with all the other gauges. The truck will blow hot air so heater core is warming up and I'm assuming the thermostat isn't stuck, and id think id at least get some kind of temp reading even if coolant wasn't circulating.


I have been reading forums and it seems as though these trucks either had 1 or 2 temp sensors/sender for this model year. The only sensor I can find on the manifold is behind the alternator to the passenger side of the thermostat. It is a 2 wire sensor with a 2 wire plug on it so I'm assuming I have the single sensor motor? everything I read says if it had 2 sensors there would be a 1 wire sender going to guage on passenger side of thermostat, and 2 wire sensor going to ecm on the driver side of thermostat.


what I don't get is that the idiot light is not on, so assuming that is the 1 sensor truck with it sending temp signal to both ecm and guage, is the ecm receiving signal still? it must be for it not to throw the check engine light correct? I replaced the sensor with no change. the wire connecter looks good no corrosion.


I have a 180 degree thermostat to put in this weekend, guess ill see if that does anything.

 

The PCM will not throw a code unless it is "too cold for too long" or if it gets over 240 or so. I forget of the ECT is ground reference or 5V.

 

So if it's a new sensor, and the guage functions, it must be wiring to guage? Is the signal going directly from sensor to guage or is signal coming from ecu. I'm assuming it must be wiring since there isn't a code and I've been driving it long enough it should've thrown for being cold by now. Anyone have a service manual or wiring schematic for a 98 dakota? I can't seem to find one.

 

The signal comes from the PCM. All the gauges are run off the CCD bus and not direct wired.

It still could be a bad sensor.

On connector 1 of the PCM the sensor ground is pin #4, the signal is pin #16.

We don't have 1998 manual for download but the 2000 is very close. 2001 and up are very different. You can get the 2000 manual from this link:

https://dodgeforum.com/forum/2nd-gen...-download.html

 

So I should try another sensor?

 

It could be a wiring problem too.

I'd disconnect the battery and then remove the connector from the PCM to check continuity to the temp sensor. If that's good, I'd check the resistance when cold and hot.

 

What resistance should I be getting hot and cold from the sensor?

 

I don't have the spec on that. But it should vary and you could compare it to another sensor.

 

Page 257 or so of the FSM PDF; Section 7 page 36.

Sensors vary widely, but I would expect something like 30-60 K-Ohms cold and 1-5 K-ohms hot.

 

I would suspect wiring usually the wires brake in the insulation just at the sensor connector at first gaze they look OK. Almost all my sensor connector wires have gone bad on my Dak so its common.