How to Troubleshoot a Car Engine Temperature Gaugeby Robert Moore
Items you will need
Repair or Service Manual
Deepwell socket set
Find the coolant temperature sensor.<p>The location of the sensor varies depending on what year, make and model of vehicle you are working on. It is commonly found threaded into the engine block, thermostat housing, cylinder head or upper intake manifold.</p>
Check for reference voltage to the sensor.<p>Disconnect the wiring harness from the sensor. It may have two or three wires. Review your repair manual to determine which wire supplies the reference voltage. Set your multimeter to read <strong>DC volts</strong>, on the <strong><a href="http://myslu.stlawu.edu/~jmil/physics/labs/common/multimeter.pdf">20-volt scale</a></strong>. Connect the negative lead of the multimeter to a good ground -- ideally the <strong>negative battery terminal</strong> or one of the <strong>body-to-engine grounds</strong>. Touch the positive lead from your meter to the <strong>reference supply wire</strong>. You should see 5 or 12 volts with the ignition key in the “On” position, depending on how your vehicle is designed. Proceed to the next step, if you receive a <strong>voltage reading</strong>. If you do not get a reading, check any fuse labeled “Engine,” “ECM” or “PCM.” If all fuses are good, trace that wire back to the computer and repair any damage to the wire. If there is no damage to the wire or any blown fuses, the <strong>computer</strong> is likely at fault.</p>
Test the coolant temperature sensor.<p>Follow the steps in your vehicle’s <strong>repair manual</strong> to release the <strong>pressure</strong> in the cooling system, and then drain the coolant.</p>
- Do not attempt to open the cooling system when it is hot -- severe injury or death can occur.
- Coolant has a sweet smell to animals. Store the used coolant in a place away from children and animals until you can dispose of it.
Check the sensor return wire<p>Review your vehicle's repair manual to determine if the sensors return wire runs directly to the <strong>instrument cluster</strong> or back to the <strong>computer</strong>. If it goes back to the cluster, follow the directions in the manual to remove the instrument cluster. If it goes to the computer, follow directions to access the computer. Set your multimeter to the <strong>20-volt</strong>, <strong>DC-current</strong> scale and probe the return wire at the instrument cluster harness or the computer harness. You should see a voltage <strong>lower</strong> than the initial reference voltage you found in Step No. 2. If you do not get a reading, check for damage to that return wire and repair it as necessary. If your sensor reports directly to the instrument cluster, and you do not receive voltage, <strong>replace</strong> the <strong>instrument cluster</strong>. If your gauge is computer controlled, check for return voltage on that wire at the <strong>computer harness.</strong> If there is no output voltage from the computer, <strong>replace the computer</strong>. If there is voltage being sent from the computer to the instrument cluster, check for that voltage at the cluster. If you get voltage at the clusters wiring harness, replace the instrument cluster. If you do not see voltage at the cluster, but you got a voltage reading at the computer, inspect that wire and repair as necessary.</p>