Coolant Temperature Sensor 94 C1500 350TBI

[kvgsqtii]

Have a question about the function for the coolant temperature sensor located in the intake manifold right by the thermostat housing.

The temperature gauge hasn't worked since I bought the truck a couple years ago. Finally decide to fix it. I knew the gauge was functional, because it would perform the full sweep when the key was turned to on. I looked in the engine and found the temp sensor on top of the intake Manifold and assumed that was the only one. Replaced it and no luck, gauge still not working.

Since then I got a copy of the factory service manual and have run through the diagnostic steps for the temp gauge not working which led me to finding the other coolant temp sensor located in the side of the driver side cylinder head. This is the only temp sensor discussed at all (that I can find) in the fsm.

Does anyone know what the purpose of the first temp sensor is?

Intake manifold coolant temp sensor

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Item 22 in the figure below

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Continued in next post

 

[kvgsqtii]

Temp sensor in cylinder head

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It's unplugged because I was testing it

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Item 22 in the figure below

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[RichLo]

Intake manifold is for the engine computer. The drivers side head coolant temp is for the gauge

 

[kvgsqtii]

Intake manifold is for the engine computer. The drivers side head coolant temp is for the gauge

Thanks for the quick answer. Is it the same sensor?

 

[someotherguy]

Definitely not the same sensor. Works on same principle - range of resistance. The higher the resistance, the colder the temperature reported.

As you can see in your own pic, the one in the driver side cylinder head just has 1 pin. The connector shape is a 2 pin style but there's only one cavity and pin in there.

The one on the intake has 2 pins. BTW it is critical this one is in good condition and working as expected; it has huge impact on the fuel mixture, so it will affect how well your truck runs and its MPG.

The grounds at and next to the thermostat housing are critical, too.

Richard

 

[kvgsqtii]

That makes sense. I cleaned the stud and replaced the ground terminal ring on the t-stat housing when I replaced it and the t-stat when i also replaced the temp sensor.

I'll get a new temp sensor to replace the gauge sensor this weekend. Will be nice to have a functioning temp gauge finally.

Thanks for the help.

 

[Schurkey]

Ground the "one" pin in the connector for the sending unit in the cylinder head.

Gauge needle should sweep to full-hot. If it doesn't, the problem isn't the sending unit.

 

[kvgsqtii]

Ground the "one" pin in the connector for the sending unit in the cylinder head.

Gauge needle should sweep to full-hot. If it doesn't, the problem isn't the sending unit.

It did. Followed the diagnostic steps in the fsm to check it and its definitely the sensor.

 

[evilunclegrimace]

Just for a point of clarity; The unit in the manifold is a sensor (A thermister to be precise) and the unit in the cylinder head is sender.