Hello all. My 2004 V40 has cold start problems, and after months of troubleshooting, and checking & replacing almost everything, I am convinced the problem lies in the ECT sensor or wires.
Two questions:
First, is it possible for the temperature sensor to send a partial signal? Meaning, could it just send a signal to the gauge in the dashboard, letting me know the engine is cold or warm, but not send the signal to the computer, allowing it to adjust the air/ fuel ratio?
Could the sensor or wires be bad, yet show the correct temperature on the gauge on the dashboard?
Second, I want to run new wires from the ECT sensor to the computer, but I don’t know which pins or wires go where. Does anyone know where they plug in on the computer (ECM)??
Your help is greatly appreciated.
Thank you!

 

1) easy enough to test the temp sensor - its located under the thermostat housing - follow the upper radiator hose to the block and its under that. you'll see its connector just off to the left of the thermostat. Measure resistance - should be high -ie 3000-5000 ohms cold (depending on ambient - google for a chart). When the engine warms, the resistances drops to under 300 (- ie 200ish at running temp). If unsure, you can remove the ECT to test. Truth is, if you go the the bother to find the connector and remove the ECT, you might as well replace the sensor and the thermostat. I wouldn't assume computer wiring is bad - I'd start with more common, simpler causes 1) bad ECT sensor 2) intake air leaks/torn vacuum lines 3) exhaust leaks (particularly at the flex pipe). To ease your curiosity, wiring diagrams can be found on line. You can also consider removing the ECM clean its connectors with electronics cleaner and reinstall (but again, not a common fault area).

 

Thank you for your help. How exactly do I test the resistance? I have a multimeter, but I don’t know what goes where. Thanks.

 

your multimeter should have a setting for ohms - (check to see if it has specific ports for the cables to plug into for ohms vs KOhms - numbers you are looking for is +3000 cold so chose the appropriate range. Ohms get measured by touching the probes to the two leads to sensor when the connector is disconnected - you may need to flip the probes incase the needle goes backwards.. No voltage from the car should touch the probes when measuring resistance. I bet you can find a vid on Youtube...