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Old 02-16-2008, 06:58 PM   #1
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Default Yet another question about OBD2...

Got something rather interesting in my testing...pin 16, blue connector, is supposed to be a 5 volt reference, according to schematics and pinouts. BUT....I just put it on my DMM, and it is registering battery voltage...something is not making sense.
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Old 02-17-2008, 08:06 AM   #2
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Anyone?
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Old 02-17-2008, 03:39 PM   #3
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I see this was moved and I don't know how to find the previous.
Q: To which connector are you referring (blue)?
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Old 02-17-2008, 03:50 PM   #4
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Ah...so it was moved...'tis ok.

I refer to one of the two connectors at the 1996-up PCM. Blue connector, pin 16. In everything I see, even the 1993 schematics, show that the MAP sensor and TP sensor uses a 5 volt reference, which I am not debating. What I AM curious on, though, is why this pin is registering battery voltage instead. And, yes...I took the harness off of the PCM to see if I wired it wrong and there are 12 volts going into it....and there isn't, so I know that my wiring is correct on that.
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Old 02-17-2008, 05:59 PM   #5
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All I have is the 93 manuals and I cannot find the MAP sensor (Manifold Absolute Pressure?), so I cannot be of much help.

But one of the golden rules of "tronics and tricity" is that if you read source voltage across something, there MAY, MAY be an open in the ckt and you are reading across it. All depends on the circuit. Maybe a missing ground. Don't want to lead you astray.

Like, on my MAF sensor (not MAp), if I read B+ from it at the PCM, I would suspect an open ground at the sensor, esp. as it has full B+ on one side of it.
I'm totally babbling here.
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Old 02-17-2008, 06:08 PM   #6
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There will be a MAP sensor in the '93 FSMs...you just gotta know where to look

It'* NOT going to be in the emissions and driveability section...no need for it there. It WILL be in the electrical section, under dash and gauges...since in 1993, the only thing the MAP sensor did was to tell you what the boost/vac is.
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Old 02-17-2008, 07:33 PM   #7
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I am guessing that in 96-up the MAP also feeds to the PCM, but not 93s(?). Just feeds the gage in 93. right?

Anyway, there is a source for 12+ v via the gage, through its solid state ckt. So if pin 16 is connected in anyway to the gage, you could be getting an open from the MAP side and reading the 12+ from the gage ckt.

Just a stab.
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Old 02-17-2008, 07:50 PM   #8
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If that were the case, I would have read 12v with power on, and blue harness head disconnected from the PCM, and positive probe to the pin (and negative to ground).

I didn't. 2 millivolts if memory serves...not even enough to worry about.

My next trick I think is to have the harness on the PCM...minus the wire that comes out of pin 16. If I probe that pin, and I read 5 volts at that time, then I will know something is up with that circuit,

Oh...starting in 1996, ALL vehicles had MAPs, not just supercharged ones. BUT...when they are supercharged and have a boost gage, then they will have two MAPs...one for the PCM, the other for the gage.
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Old 02-17-2008, 08:15 PM   #9
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My bad. I interpreted "battery voltage" in the first post to be +12v.

I'm taking my nap now.
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Old 02-17-2008, 08:34 PM   #10
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99 FSM shows pin 16 as a ground for the PCM. Are the PCM'* different from 97 to 99?
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