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I have a 1991 Toyota pickup 3.0 V6 the problem started when the temperature gauge acted weird going up and down. After, every time when I turn on the ignition switch, the water temperature gauge in the instrument cluster goes up to the maximum even without running the engine. It will still being UP to the max temperature without reason. I have replaced the water temp sensor, the ECU, the instruments gauge cluster and still does not fix the issue. Same issue happen. Everything else (all gauges) works fine in the instrument cluster, but the water temperature still does not work. I will appreciate any help. Thank you
Hi, If the temp gauge still registers max when the sensor unit is disconnected and as you have replaced all the components in the coolant temp gauge circuit, that only leaves two possibilities. There is an earth connection on the wire between the coolant sensor unit and the ECU or on the wire between the ECU and the gauge You need to check the wire that it is not pinched or that the insulation has been worn and the wire is exposed and that it may be touching the chassis or other metal parts of the vehicle. Couldn’t find a wiring diagram for your year model but found the one below which may help. Also I don’t know the vehicle and there are two temp monitoring devices shown. A coolant temp switch and a EFI coolant temp sender. If the sensor you replaced has two wires connected then it is the EFI sender (green box) and if only the one wire it is the switch. (red box) Hopefully the wiring is the same for your year model and that you can disconnect the appropriate wire from the ECU (check the wire colour is the same at both ends, ECU and sensor to make sure) to help narrow down the problem location. If you disconnect the wire at the ECU and the gauge doesn’t move then the problem is between the sensor and the ECU. If you disconnect the wire and the sensor still moves then the problem is between the ECU and the gauge
(click on image to enlarge for better viewing) Hopefully a start
