TESTING

Before going to the trouble of removing the sender from the engine block and testing it, perform the tests presented in the accompanying chart to ensure that it is the sender malfunctioning, and not another part of the circuit.

1. Remove the coolant temperature sender from the engine block.
2. Attach an ohmmeter to the sender unit as follows:
   1. Attach one lead to the metal body of the sender unit (near the sender unit's threads).
   2. Attach the other lead to the sender unit's wiring harness connector terminal.
3. With the leads still attached, place the sender unit in a pot of cold water so that neither of the leads is immersed in the water. The portion of the sender unit which normally makes contact with the engine coolant should be submerged.
4. Measure and note the resistance.
5. Slowly heat the pot up (on the stove) to 190–210F (88–99C) and observe the resistance of the sender unit. The resistance should evenly and steadily decrease as the water temperature increases. The resistance should not jump drastically or decrease erratically.
6. If the sender unit did not function as described, replace the sender unit with a new one.