9550

so, im checking voltages of various sensors. using the haynes manual as a reference, i probe the "signal" contact with my red lead, and the ground with black. im getting negative voltages in a couple spots. if i switch the leads, i get positive voltage. i did it with 2 different meters
for example, i backprobe the tps and i get like -0.9 volts at idle. if i switch the meter leads and put the red probe on the "ground" and the black on the "sig", i get +0.9.
doesnt make sense unless the haynes manual is wrong?
does it make a difference?

mjr46

what makes sense is you are using the meter backwards!!! with a dvom it flows the current in one direction, if you hook it up backwards it'll read a neg coefficient, the black should always be used as a ground and the red to probe b+ 12 v sources

SSFenris

VDC always has polarity. VAC does not, but your car also has no VAC circuits (your alternator is designed to spin, not wobble). I'd check your pin-out again, and check the connection of your leads to your meter (black to the terminal labeled with lines, red to terminal reading 'volts'). In general, in a situation like that, I'm looking for amplitude of the signal, not polarity (the car worked at one time, yes?) Your alternator can only output voltage with one polarity, so by saying 'it's reversed in SOME spots', makes me wonder. Did someone hack up your harness? Polarity doesn't just 'reverse' without a good reason.

mjr46

Reread his post you are misunderstanding what he is doing......he's talkind about first using the positive lead on DVOM to check circuit then he reverses to back probing with the neg lead and then sees same reading but only a neg reading...what is occuring to him is just what I stated above

9550

no, actually i did it the same way both times, only reversed the probes.
put pins through the back, red on sig, black on ground, checked with key on, got negative reading, switched the probes and got positive reading. used two different meters, same results. the meter leads are definitely in the correct plug.
i still could be doing something wrong(and not understanding the replies here), but i just want to be clear. im fairly handy with meters and familiar with voltage and current and such. im no electrician, but i have a pretty good clue (at least i think so 8-) )

and actually, when i said a couple were wrong, i only checked a couple, and they were like that.

the car idles well enough when its cold, but once it warms up, the idle struggles (loping) and finally dies. so i started checking some sensors.

this entire exercise is really one big crash course for me, i appreciate the patience

Joel5.0

Start with the basics, confirm correct polarity with the battery and make sure you are reading VDC. You should also start by checking what the ECM is interpreting in terms of working conditions, run a set of DIY KOEO/KOER self tests and LUK.

9550

yeah, i did the code check
the codes didnt make sense, but best i could figure was a 122.
i say it didnt make sense because it repeated the 122 twice. there is a definite possibility that i was not adept in reading the codes.
when the test first started, there was a very very very quick flash of the cel (i used the cel, not a meter). it didnt even completely light up it was so brief.
i will try to run it again in the near future.

Joel5.0

122 - TPS circuit below minimum 0.6 volts (O), TPS circuit has intermittently failed below minimum 0.6 volts (M)

The initial flash is the fast codes flash and it's normal, then the CM codes are flashed twice, separator code (1 flash) and then the CM (Continuous Memory) codes are flashed twice. Check the examples and the video in the link.

SSFenris

So, you put the (+) lead on your signal pin, your (-) lead on the ground pin, and you're getting a negative voltage?

9550

so it seems