In attempting to diagnose my no spark problem, I checked the thermosensor by pulling out the harness and attaching a test light to each of the w wires while the ignition was in the on position. I got no voltage.

What could cause this? A broken wire somewhere?

 

Have you tried measuring pin 2I (Green/White wire) of the ECU w/key to on and the sensor plugged in? Should read 2-3 volts cold and close to .5 volts engine fully warmed for an S4.

 

Bone cold and it reads .2 volts. Is that indicative of a faulty thermosensor?

 

Do you get 5 volts w/the sensor unplugged w/key to on and engine cold?

 

I just tried it again to make sure I measured it correctly..
I unplugged the harness from the sensor and I unplugged the harness from the ecu and measured there.
Engine cold, key in the on position, this time measured .03 volts.

 

The voltage that would be present on the G/W wire w/key to on comes from the ECU so you cannot unplug the harness from the ECU.

 

ok. I plugged the harness into the ecu, pulled the harness out of the thermosensor and measured there .. 5.05 volts.

I guess that's the voltage i s/b getting, so I've gotta assume that wiring is ok.

If the wiring's ok but the thermosensor is bad, would that cause an issue with cold starting? (no starting).

 

The sensor selects how much fuel to use when starting the car based on the coolant temp so normally the engine would inject more fuel when starting the car. W/everything plugged in and the reading taken by backprobing the ECU it should read 2 to 3 volts cold and if it still reads .2 volts then your sensor is likely in need of replacement.