Oceanbrave,

My mistake, I did the readings again on my old sensor as indicated below and I will redo my new sensor which is reinstalled in my car tomorrow.

black on pin 2 and red on pin 1 I get 1.524 DC V
Black on pin 1 and red on pin 2 I get 0.575 DC V

Maybe nothing wrong with this old sensor?

 

Hmmr reviewing your post further I have the following observations:-

• The great new is you have a really great meter! However if your picture is an actual test, then with 100% confidence the Fluke Multimeter is set on the "Capacitance" range as mentioned previously. This is the wrong measurement parameter, only the Diode Test function works for us, it's a bit like ordering whisky but then getting milk instead

• Re. the old sensor tests, these readings look the same as mine, however the scales are 1000 times too small ! I think you will find your values should be kΩ (x 1000) and not Ω (Ohms) i.e. 6.327Ohms => 6.327kΩ or 6327 Ohms, 198kΩ and 195kΩ. This only really matters if you consider that 6.327 Ω at 5 volts consumes 4 watts instead of 4mW i.e. 1000 times more.
• Regarding the new sensor, hopefully the 56.4 Ohms value is really 56.4kΩ otherwise that could be telling us something. In contrast your 34.5MΩ values look sensible.
• Your jumper tests show the ECU is working, 0.02V will be the floating voltage (29 psi) which I imagine is roughly the same psi as with 3&1 jumper, and the 4.25V looks sensible - so that's really good news ✔️

So bottom line, put the Fluke on Diode Test and check both sensors again, also be mindful of the ohms scales (take pics if in doubt) and in particular check that 56.4Ω value, but I'm pretty sure the Diode Test will reveal any problems there.

Though electronics is a bit technical, however you have got a Fuke (I assume it's yours and I'm jealous) which I notice still has its screen protector on it!

My fluke literally came out of a trash can 22 years ago, my 10yr old son fixed it and I've used it ever since, never owned a new one.

So below is a replica of the test you did, I would pretty much expect you to measure similar results for the old sensor, the new one is a bit of an "unknown" at the moment. Note the reads 0.597V, not ohms or nF, but actually the volts drop of a forward conducting diode - highly significant for us.

 

OceanBrave,

I have rechecked my old sensor again with photos, see below results;

1. Ohms test across pins 2 & 1 was 6.326 KOhms
2. Ohms test across pins 1 & 2 was 4.270 KOhms
3. Ohms test across pins 3 & 2 was 194.8 KOhms
4. Ohms test across pins 3 & 1 was 198.1 KOhms
5. Diode test across pins black 1 and red 2 was 0.567 DC V
6. Diode test across pins black 2 and red 1 was 1.525 DC V

1. 
   
   

 

Hmmr good job, and great results ✔️

Great pics too, that pretty much nails things measurement wise, BTW your figures are the same as mine but with one exception as I'll explain.

So a couple of things:-

Step 5
This is key step and clearly identifies the power pins with Black = +5V Ref, Red = 0V and the remaining pin being Signal ✔️

Step 2
Compared to yours my sensor measures the same ohms value across pins 1 & 2 in either direction i.e. it's impossible to identify which pin is which from these two results.
Unlike the diode test voltage, resistance values tend to vary between sensors, however the fact your sensor shows 6.326kΩ and 4.270kΩ may indicate there is an internal issue with it (possibly)

On the sensor production line, manufacturers will run the exact same tests as you did using automatic test equipment to quickly throw out any suspect devices.

So the $64 million question is about the new sensor's polarity - Which pins give the 0.6V ish value on diode test ? (assuming the new sensor has a similar internal arrangement)
Run the exact same tests on the new sensor and if we are lucky they'll provide the answer 🤞

 

Oceanbrave,

I agree, Scotch straight up will do me just fine.

I did the tests the easy way this morning, I didn't remove the compressor kit from my car, I just unplugged the computer and fitted pins in to 3, 11 & 19. I have attached a verification photo of this below.
The most important test being the diode test across pins 1 & 2 were interesting
The diode test with black on pin 1 was 1.915 DC V
The diode test with black on pin 2 was OL DC V and I checked this many times.
And there was no Beep from the meter indicating either direction was correct
The Ohms test across pins 1&2 was 56.37 KOhms
The Ohms test across pins 2&1 was 56.27 KOhms
The Ohms test across pins 3&2 was 10.55 MOhms
The Ohms test across pins 3&1 was 10.52 MOhms

 

Just quickly, did you try the diode tests involving pin 3 ?

Eg
1 to 3
3 to 1
2 to 3
3 to 2

If so then 1 and 2 seem to be the power pins with pin 1 = +5V, 2= 0V and 3 = Signal

Does this match your data? (Not at my pc so can't check)

 

Oceanbrave,

I did the Ohms test as you suggested across pins 3&1 and 3&2 both ways and all were OL DC Volts

 

Sorry it was the diode test, not Ohms

 

Oceanbrave,

You stated earlier for a diode test across pins 1&2, "the lowest reading only occurs for the power pins" therefore if my readings are 1.915 DC Volts with black on pin 1 and OL DC Volts with black on pin 2, wouldn't pin 2 be the +5V pin, the opposite to what it should be therefore I need to swap pins 1&2 around ??

 

Hmmr many apologies for the time delay, I'm in the UK so we're maybe across time zones?

Again great pictures all worth 10,000 words, plus I have a few points.

Point 1
"You stated earlier for a diode test across pins 1&2, "the lowest reading only occurs for the power pins" therefore if my readings are 1.915 DC Volts with black on pin 1 and OL DC Volts with black on pin 2, wouldn't pin 2 be the +5V pin, the opposite to what it should be therefore I need to swap pins 1&2 around ?"

For a diode, the black probe would indeed indicate +Ve as 1.915V would be the lowest reading as OL is "Out Of Range" i.e. higher not zero

Anyway this logic only applies for values in the 0.7V range (Silicon), but ironically you could still be right as I'll explain later.

Point 2
I have the same harness+sensor and set-up here on my work bench, so to check I just verified your connections along my connections and a diagram which I made a while ago, so I think we are all good! (pictures below)


So for the record, I repeated your tests with the results below, showing Connector Pin Refs (not the sensor) and your readings in brackets():-

Possibilities
The new sensor does appear to behave differently, so it possibly has no internal diode (may use a more modern way of transient suppression)

The ** figures for Tests #3 & #4 are the lowest resistances for both sensors, so we could assume "Power Pins"

So working on the basis there's "no diode" the new sensor has no value for Test #4, but the old sensor Test #4 (1.824V) & new sensor Test #3 (1.915V) have similar values, so this possibly indicates the new sensor is indeed reversed.

At this point I'd say it's worth swapping pins 1 & 2 because you have the correct wiring, the sensor isn't working and it's most likely already wired in reverse (so nothing to loose?)

Also the GM drawing could be wrong, and it's worth noting it shows the "connector pins" not the "sensor pins" which appear to differ from other similar sensors out there (as I posted earlier)

Of course I can't guarantee anything and these are only suggestions. It would be a "no brainer" if we had an unlimited source of sensors (but alternatives may still be available for that thread size)

Just hope you get it working, my goodness you've done enough work on this...