Temperature gauge not working?

MINOLEE

MEMBER
1994 CHEVROLET CAPRICE
4.3L
V8
2WD
AUTOMATIC
212,987 MILES

When the car is off the Temperature gauge reads cold. As soon you turn over the key the gauge goes below cold. When you start the car, the gauge goes to hot then drops under the cold mark and stays there. I've replaced the temperature sensor and thermostat. Where is the fuse to check and see if it's blown? If it's not the fuse. Where's the wires go from the engine to the dash?

1 Reply

JACOBANDNICKOLAS

MECHANIC
109,709 POSTS

Hi,

There could be a couple of different causes. As far as the engine coolant temperature sensor is concerned, you have replaced that without any change.

The ECT is nothing more than a resister that is controlled by temperature. The computer sends a 5-volt signal to the coolant temperature sensor through a resistor in the PCM and measures the voltage. The voltage will be high or low depending on the coolant temperature. By varying the voltage, the computer will sense the engine coolant temperature.

So, at the sensor, there will be a yellow wire and a purple wire. The yellow one is the power supply. Disconnect the connector and probe the yellow wire. With the key on, you should have approximately 5v. If that is good, then confirm continuity to ground by probing the purple wire.

If these two wires both pass inspection, the issue is likely at the cluster itself. Let me know if this is something that started all at once. Also, let me know if you have checked the connections on the cluster.

Here is a link you may find helpful:

https://www.2carpros.com/articles/how-to-check-wiring

Keep in mind, for the temp gauge to go the opposite direction, the battery voltage polarity needs to be reversed, so I have a feeling it is in the cluster.

Let me know what you find.

Joe

See pics below.

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