Temp. Sensor trouble shooting.

The check engine light on my 98 came on with a P1281, which is a code meaning that the engine is not heating up fast enough. The temp gage in the dash has not been reading right for a few weeks. It’s been reading very low or not at all and sometimes jumping up to normal. I have put off fixing it because I have been in the middle of moving.:nono:

Does the computer get it’s temp info from the same gage as the dash? Is the gage for one or both the one in the water hose fitting thing right above the fan? If so how can I test the gage and the wiring?
Thanks in advance.

98 uses a single sensor to feed computer and gauge. either the sensor is going bad or you have a coolant problem. I had that problem when the coolant passage was blocked off

So what coolant passage was blocked? How did you discover that? Was your rig over heating?

And that sensor is at least eleven years old now - so it's probably due for a change. It's a fairly simple part to change, and if you're quick you won't lose much coolant.

If there's a single wire (I've not seen it,) use RTV Copper to seal the threads. If there are two, use PTFE. The reason for the RTV Copper on the single-wire version is to preserve the ground (since the one-wire sensor grounds through the threads, while the two-wire does not. Yours is likely the two-wire.)

Bronco said:

So what coolant passage was blocked? How did you discover that? Was your rig over heating?

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When I was given the thing on of the OBDI codes in the computer was "too cool too long". Later on when I got around to doing a flush and fill the head was bone dry--the heater core was blocked and air had been trapped in the head

The 98 is indeed a 2 wire sensor, and in a nice location to keep you from making a mess of things. Shouldn't take but a minute to swap one. If you want to verify the sensor's bad, I'm pretty sure the resistances across a normal range of temps has been posted around here, but you'd have to search a bit to find it.

Try disconnecting the temp sensor, then shorting the wire (harness) ends that connect to the temp sensor in the thermostat housing, then but don't short the 2 harness wires, try both with the engine running. If one reads all the way to the left on the dash gauge, the other all the way to right, then the gauge and wiring is good to go, you just need a new sensor. Otherwise, you have a wiring problem!

Ecomike said:

Try disconnecting the temp sensor, then shorting the wire (harness) ends that connect to the temp sensor in the thermostat housing, then but don't short the 2 harness wires, try both with the engine running. If one reads all the way to the left on the dash gauge, the other all the way to right, then the gauge and wiring is good to go, you just need a new sensor. Otherwise, you have a wiring problem!

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Why didn't I think of that? I like it. Anyway to picked up a new one (16$ @ autoZone) and it's all good.
Thanks for the help