ECT 5 volt reference

[wales660]

My ECT 5 volts reference is dropping to 2.3 volts when the sensors is plugged in. What could be causing the volt drop please? Also return voltage to the ECM is nothing at all

Thanks

Jeff

 

[static zap]

The ECT sensor may be no more than a simple "resistor" that varies its value with temperature. If it has 2 cables 1 may be an earth reference and the other floats high to 5V open circuit , but is pulled down by varying degrees depending on engine temperature.
(Unlike active sensors that may have a steady +5 feed and even pulsed outputs ! )
[automerge]1574032799[/automerge]
Found an example from After market Emerald kit .

 

[wales660]

Hi I understand what the diagram is but this is an engine coolant sensor which talk to the engine control unit using voltage to determine the fuel trim to the injectors. The engine control unit looks for a voltage range to work with. Eg. 5 volts being say 5 degrees and 1 volt being 90 degrees . Open circuit being a default of say minus 40 degrees. My question is I have 5 volts to the sensor wiring plug until its plugged into the sensor and once plugged in the voltage drops to 2.3 volts and when then measuring the voltage which is supposed to pass through the sensor and be adjusted via the sensors resistance according to the temperature of the coolant in the engine. My return voltage is Zero talking back to the engine control unit constant regardless of the temperature. Is this a duff sensor or is the wiring at fault? Any suggestions on how to determine this will be much appreciated.

 

[static zap]

You are confused with how it works , your 2.3 volt is the reading ,It should vary between a cold engine and a hot one
(Hot normally lower if i remember right. ...)
Earths measure 0V to earth if they are good !
(but maybe something else when cranking -hence separate !)
.. Forgotten typical volts at moment (been a few years !)
reading live data should turn that into a figure -if way off -Sensor( May be to blame)

 

[wales660]

You are confused with how it works , your 2.3 volt is the reading ,It should vary between a cold engine and a hot one
(Hot normally lower if i remember right. ...)
Earths measure 0V to earth if they are good !
(but maybe something else when cranking -hence separate !)
.. Forgotten typical volts at moment (been a few years !)
reading live data should turn that into a figure -if way off -Sensor( May be to blame)

Hi

The 5 volts is my supply voltage to the ECT so you saying the supplies voltage is changed by the ECT resistance and travels back down the same wire? My understanding is 5 volts reference will enter the ECT on one leg and as there’s a resistor which is variable to heat it will alter the voltage exiting on the other leg. What I’m saying is my supply voltage is 5 volts unplugged from the sensor and 2.3 volts plugged in and still measuring the volts going into the sensor by back probing it. There’s no voltage leaving the switch on the exit leg. Also there is no continuity on the exit plug to ground which tells me it’s an ecu ground not a vehicle ground. I think I should be seeing 5 volts entering the ECT and see lower voltage exiting the ECT which will be the information for the ecu. I’m unable to look at live data as it’s a Japanese import which wil not talk to a scanner. Even Mitsubishi dealers don’t have a scanner for it.

 

[plugsandsparks]

It depends... the 5V reference you talk about could have a built in pull up resistor inside the ECU, so when open cct you will indeed see 5v but put any resistance into the cct and it will reduce proportionally

 

[wales660]

It depends... the 5V reference you talk about could have a built in pull up resistor inside the ECU, so when open cct you will indeed see 5v but put any resistance into the cct and it will reduce proportionally

Ok thanks vehicle electrics work in mysterious ways

Thanks

Jeff

 

[static zap]

Found a Citroen vid that mentioned over 2V cold ,showing 2.5v
(results will depend on how cold ..brrrr...)

View: https://youtu.be/zIMjsrOvCqU

( I wimped out on the practical approach )
Just don't think water ingress..

 

[wales660]

Hi

I get it now but must admit i was looking at it totally wrong , thinking the sensor ground was summin else. Thinking of it now with sensor grounds being sometimes shared i dont know what i was thinking there. Guess i didn't understand the circuit. Just need to work out now what the voltage should be present at different temperatures to ensure it's getting the right information to correctly function.

Thanks

Jeff

 

[static zap]

I think getting over complicated is part of our nature , I was amazed watching my dad with a thermostat thrown in a bowl of near boiling water. Plenty of sales literature about ABS ,and crank sensors ... When they get complicated enough to self calibrate ,things will get really confusing !
..the joys of innocent looking TPMS..

 

[plugsandsparks]

I do car electrics as part of my hobby ( a reluctant but necessary chore)
Replacing OEM electronics is where i am at the moment. Have two sensors that i have left to last - Gearbox oil temp and engine oil level, no idea what they are - so trial and error to get the calibration done..... :-(