In the example attached all that is mentioned is Signal Return (PCM Pin 46) and ECT Signal (PCM Pin 7). I have the EVTM and can chase all of that no problem. I guess the crazy question I have is this; Is the signal return the 5VDC line while the ECT Signal is the thermistor adjusted Voltage heading back to the PCM? I have to believe it is. Although what's odd is that with the connector disconnected from the sensor I read about 5V on EACH PIN. That quite simply can't be correct in my mind unless I'm crazy. Starting to think I have another issue but I have to wait until the weekend to dig in.
Again - sorry to beat this thread up again but does anyone have an accurate account for what Ford means when they use the term "Signal Return"? In the EVTM it's common to a BUNCH of sensors - I highly doubt its anything other than a 5V feed into each sensor.
Correct, simply a low voltage baseline. That's the 5v DC ref. out of the PCM/EEC and the
input to several sensors.
Just to be sure we're on the same page, the 'signal'* is the
output from the sensor, fed into the PCM/EEC. DO NOT ATTEMPT TO READ ref. voltages with the related connector(s) unplugged from their sensors. They -must- be read with the system live, connected and with sensor loads in place Trying to check reference voltage by unplugging the connector is a no-go.
Always backprobe, then check key on. DVOM recommended so you know it's value and not just that it's hot. This can be critical so you don't get fooled into relying on an out-of-spec reference voltage.
I read the output off the ECT via backprobing as well. After confirming 5v ref. in (might be as low as 4.5v actual), you would expect to see a voltage drop coming out from 3.51v at 50°, to 0.46 at 212°
LG/Y is signal out at ECT. This goes to the EEC. Backprobe it to check when engine runs and heats up. Ground black lead off meter to complete circuit to test. If meter does not auto range, be sure to use lower scale to read DC 5v and less. Have to admit I've never paid much attention to ref. voltage in the past. Been trying to adopt better elect. troubleshooting skills, including using a an o'scope for testing. The more you learn about sophisticated auto circuitry, the better chance you have of keeping cars like the SC going, I guess. A test light will get you only so far these days.
About your diagram... 46 should be the 5v ref. (
again, used by several circuits) ...beyond me why that diagram calls it SIG
RTN (return), tho. I'm calling radishes on that...
7 is the (
adjusted) output from the sensor/thermistor. What are 46 & 7 named in the PCM's/EEC's connector face/pinout in the EVTM?
*Note my habit is to refer to sensor output as a 'signal' (variable), and ref. voltage as a 'feed' (constant), but that's just me, so don't be confused. The factory diagrams call 7 'feed', opposite my habit. No matter, we both agree/consider 7 as the ECT's adjusted output that the EEC uses (among other inputs) to decide fuel strategy.
Sorry if I'm repeating myself here.
Ken