What's pin 28?

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#76

04-25-2020

Ziptie Mechanic

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From: Royston

Is there any reason I shouldn't try to jump 5v from the brown and white wire on the TB to the grey and red wire on the MAF?

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#77

04-25-2020

RonD

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Yes, don't do that

The grey/red wire is a ground, a reference ground, so your readings from before are correct, your meter is seeing the difference between computers ground and vehicle ground with the .0XX volts

So the grey/red wire is not the issue with the sensors

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#78

04-26-2020

Ziptie Mechanic

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From: Royston

Quote:

Originally Posted by RonD

ah! All this time I was thinking it was a 5v wire.

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#79

04-26-2020

Ziptie Mechanic

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From: Royston

Quote:

Originally Posted by RonD

I have tan/light blue wire as pin 36 for MAF sensor return
Then light blue/red to pin 88
The 2 MAF sensor wires

Red and black wires are for the MAF heater, 12v and ground respectively

Then IAT(ACT, air temp) use
Grey/red wire which is a shared wire with TPS, ECT, ISS, OSS and a few other sensors, 5volt, from pin 91
Grey wire goes to pin 39 signal wire

Pin 28 is transmission solenoid D, brown/orange wire
I looked at a few years and did not see 28 used for MAF

ah, that's why i thought the grey/red was a 5v wire.

I suppose I'll try to confirm continuity on pin 39, 88 & 36 to the MAF plug.

Btw, if the grey/red is a ground for the 5v circuit, is it 88 the LT BLU/RED that's supposed to supply 5v?

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#80

04-26-2020

Ziptie Mechanic

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From: Royston

Never mind

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#81

04-26-2020

Ziptie Mechanic

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From: Royston

Seem to have figured it out. Pins 39 and 88 have no continuity from the PCM plug to the MAF plug. So I'm just going to cut the wires at the PCM plug and jump it straight to the MAF plug.

Last edited by Ziptie Mechanic; 04-26-2020 at 11:10 AM.

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#82

04-26-2020

RonD

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Yes, grey/red will show up on some volt meters as 5v, not yours, thats why we tested the brown wire

So its a ground reference, which is actually what it is, but uses a "pull down" resistor circuit, or "pull up" I always get those confused

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#83

04-26-2020

Ziptie Mechanic

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From: Royston

Pin 88 jumped.

We have MAF data!

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#84

04-26-2020

RonD

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Cool

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#85

04-26-2020

Ziptie Mechanic

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From: Royston

Annnd IAT data.

Thanks for the help RonD!.

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#86

04-26-2020

RonD

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Very cool

So was it a single bad wire or 2 bad wires?

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#87

04-26-2020

Ziptie Mechanic

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From: Royston

Quote:

Originally Posted by RonD

Very cool

So was it a single bad wire or 2 bad wires?

Well counting the bad ground wire (black) 3 wires of the 6 had to be jumped. The black I jumped to a chassis ground on the passenger fender and 88 and 39 had to be jumped from the computers plug (few inches into the loom) straight to the MAF plug.

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#88

04-26-2020

RonD

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Its odd to have bad wires in a harness

Do you think it was a "mouse house", i.e. chewed wires, issue

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#89

04-26-2020

Ziptie Mechanic

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From: Royston

Quote:

Originally Posted by RonD

Its odd to have bad wires in a harness

Do you think it was a "mouse house", i.e. chewed wires, issue

There was a nest of something under the intake manifold. But I looked the harness over when I had the manifold off and I didn't see any damage to the wiring or loom anywhere so... I don't know. I agree with you though and it's part of what had me so irritated seeing as I have had much older vehicles with no harness issues.

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