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Temperature sensor inputs showing constant 4,9v

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I am having issues with my temperature inputs on my Motec M150. All three configured temp sensor inputs are showing a constant 4,9 volts. Water and oil temp are currently hooked up, fuel temp is not wired in yet. If i remove the sensor connector for the oil and water temp sensor the input still shows 4,9 volt. All the other analog sensors show expected data and are working great. What is wrong here? Or am i missing something fundamental about these inputs? None of them are in contact with fluids at the moment, but i guess that have nothing to do with it? I have measured the input voltage for the sensors and they are all dead stable at 4,97-4,99 volts.

All help is greatly appreciated.

That is the symptom if your sensor wasn't connected to the 0V pin (or your wiring is to the wrong connector pin). What happens if you connect the signal input to a chassis ground? Does the measured voltage go to 0 volts?

What is the measured resistance between the different 0V pins on your M150 -- and between one of the 0V pins and a BATT_NEG pin. -- perhaps you've blown a ground trace with a 12V short to 0V.

I guess working late nights on the car does not always pay off. I see i have wired +5v with the signal wire from the ecu, these are supposed to have ground + signal? Could i have damaged the sensor or the ecu by doing this?

Hi Olav,

5V+ into the temp sensors will be OK, the difference between a AV and AT is that internally the AT is connected to a 5V+ rail through a 1k ohm pullup resistor, where the AV doesn't have this. You can actually make a AV into an AT by running a 1k pullup between the 5V+ and Signal wire.

So you are saying that i have wired it correctly, +5v to the sig+ terminal on the sensor and the AT wire to the sig- terminal? When i take off the connector and measure the pins the + is dead stable at 4,9 volts and the AT wire measures just above 1v fluctuating a bit up and down.

When BlackRex said it was OK, he only meant you have not damaged your AT inputs or sensors. You do not have it wired correctly -- you need to connect to signal and the correct 0V for the channel ("0V A" for AT3 and AT4; "0V B" for AT1 & AT2).

Just wired up the sensors with the correct sensor ground instead of +5v and now all the sensors works like a charm. Thank you guys.

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