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ECT temp output.

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I am configuring my cluster temp sensor and apparently I cant share the coolant temp output between the ECU and the cluster.

I've checked the cluster and the coolant temp pin is putting out 12V.

Coolant temp sensor is seeing 5V from the ECU.

Is there a way to drive my cluster gauge off the ECU output ?



G'day Remi.

Whats the car and setup? Modern gauges are driven by stepper motors, and usually suck data out of the ecu via a network (CAN) and a micro-controller in the gauge cluster gets the gauge to where it needs to be. The older style will have separate temperature sender (its really a sensor, but the convention is to call it a 'sender' for some reason...) which will have a single pin. The gauge cluster powers the gauge, which then earth through the sender, its variable resistance adjusting where the gauge needle sits.


Its an older style 2005 gauge cluster. There is no CAN bus as far as I know.

So its basically as you described.. the cluster powering on the sensor.

looking at the schematics it branches off to the ecu and feeds 12v.

How can I make that work with what ECU is sending 5v.



The ECU analog inputs only take a 0-5V signal so it will not be suitable to connect it to a sensor that is pulled up to 12V by the gauge. You will have to fit a separate sensor.

So.. I went over the diagrams and realized I made a mistake.

I've switched from 3 prong ECT sensor to 2 thinking that its +,ground and signal.

Its not in this case.. Its ECU,Gauge and ground.

Sensor contains 2 separate thermistors.

Is there a way to replicate the signal maybe using GP PWM and a table ?



You could try using an aux output capable of PWM, and driving the gauge with that. You'd need to experiment with the PWM frequency to get the drive smooth and not have any audible hum, then generate a calibration table for the PWM duty cycle vs ECT.

Being from 2005, I would expect the gauge to be stepper motor driven though, Can you post up the documentation you've got?

All I have is the Subaru wiring diagram.


Pin 3 goes to cluster

Pin 2 goes to ECU as a signal that should provide 1.0-1.4V

Pin 1 is ground.

Why dont you use the standard "double" sensor?

Wiring harness has already been "sealed".

My only option right now is to "steal" the alternator charge indicator and use that.

That wouldnt be perfect but will do the job.

Adding a single extra lead for a different sensor is not unheard of, or that difficult. Even a sealed harness can have a boot replaced relatively easily -- you will still need the lead for the stock sensor & gauge, too.

Well.. adding any strands would be somewhat difficult in my situation as I have a custom harness with AS firewall connectors.

So stealing the charge indicator is the easiest and requires the least amount of harness work, as the alternator is right next to the coolant sensor.

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