just trying to build a test spec up for checking voltages ect of the sensors whilst connected to the ecu... i have the resistances for the ECT and ACT sensors and these are NTC sensors.... so as the temp increases, the resistance decreases.

with the 5v supply from the ecu as supply in to what is effectively a potential diveder circuit Vout=((R2xVSupply)/(R1+R2))

leads me by calculation that teh input resistance on th ecu itself is somewhere around the 2.5K ohm mark. Can someone confirm this either by measement or data book...?

with 2.5K as the R1 valve, 5 as VSupply and the sensor itself as R2, i can get a nice graph in excel of voltage across the pins of the ecu vurses temperature, instead of open circuit resistance

 

bttt, was just lookin through my old posts and found this - does anybody know...?

 

IIRC it's 3K Dave

fit a fixed resistor in placed of the sensor to confirm

 

What are u trying to do? They are NTC, but output isn't linear.

I'm pretty sure the impedence of the ECU will be much much higher than 3k as not to load the sensors. I have the Vout vs Temperature values of the sensors somwhere if you want them. I never measure resitance when checking them, i always measure the voltage output.

 

to clarify, if I read it as Dave meant it, he's asking for the effective pullup resistor value connected to 5V in the ECU which provides drive to the sensor input pin and forms the potential divider with the sensor. So technically not the "input impedance" as such

 

richm = correct

so that i can use the voltage as opposed to the resistance.....

i was looking at doing my own monitor when i posted originally - but now as the new RPlabs /MSD monitor software is available.... why both re inventing the wheel...

 

I didnt think many people went so in depth on these types of things, nice to see though