False Readings and Testing Temperature Sensor

Broken Sensor

Testing Temperature Sensor


A false temperature sensor reading could result in the engine running leaner than optimal. Contrary to the assumption that more fuel will create a hotter engine, the opposite is actually true. An engine running lean will produce a hotter explosion and produce more heat. Hence testing the temperature sensor is part of the diagnostic steps to solve engine overheating.

Depending on the design, there could be multiple temperature sensors measuring engine temperature. Systems like the ecu, dash display, or A/C cutoff could be running off their own sensor. So the temperature shown on the dashboard might not match that seen by the ECU.

It’s best to look up the sensor specifications to test accurately. The resistance can vary quite a lot from cold to hot. To test the sensor, use a multimeter to measure its resistance (ohm). Then measure the temperature at the base of the sensor with an IR laser thermal gun. If the measured temperature and resistance match the specifications, it is a good sign that the sensor is functioning properly.

In some cases, the sensor specifications are unavailable. Simply making sure that the sensor is not “fully open” and has more than ~ 50 ohm resistance is a good rough estimate. However, these are often cheap and can be a good idea to replace if in doubt. I’ve seen more than a few outside their specs and even some intermittent failures.

The Grotto fan controllers have a built in engine overheating alarm. As they rely on the stock temperature sensor so their correct function depends on an accurate sensor.

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