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Drive By Wire Question

imp

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59 Ranchero F250 D'Line
Below is the schematic from Ford Shop Manual showing the Throttle Actuator Control wiring. I circled the portion which feeds the throttle plate drive motor, wires number 1835 and 1836. Lacking the Powertrain Control/Emissions Data Manual, my shop manual has no info on expected resistance or voltage readouts.

Does anyone know whether those two wires are anything special, like resistance wire? Should I not read nearly zero ohms along the length of each wire? I disconnected at PCM and TPS, and am measuring directly connector to connector. Any help deeply appreciated. Fighting a P-2106 "TAC Forced Limited Power" DTC now for weeks! imp

 



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They'd be designated as 'VREF' if they were voltage sensitive.

Interesting, they are both listed as voltage send and voltage receive (+/-) yet 1835 is listed as motor feed and 1836 as motor ground. So if there is an issue with the motor and it's sending back an incorrect value, that may cause the P-2106.

Though, many of the other parts on that page are a referenced voltage.

I watched this video some time ago, it looks at the different components/causes.

As far as line voltage, or OHMs resistance, I was testing line integrity of my charging system to PCM wire. Using a 9 volt battery, from connector C139 to C102a, I registered 9 volts, but from the PCM connector (C175a) to C139, it only read 3 volts. There's no resister inline, so I can't explain that one. But I'm not an electrical engineer. The issue for me lied with the connector C102a being faulty. The prongs in the connector were corroded or loose. Wiggling it got it to work for a period, then issues.
image.jpeg
 






They'd be designated as 'VREF' if they were voltage sensitive.

Interesting, they are both listed as voltage send and voltage receive (+/-) yet 1835 is listed as motor feed and 1836 as motor ground. So if there is an issue with the motor and it's sending back an incorrect value, that may cause the P-2106.

Though, many of the other parts on that page are a referenced voltage.

I watched this video some time ago, it looks at the different components/causes.

As far as line voltage, or OHMs resistance, I was testing line integrity of my charging system to PCM wire. Using a 9 volt battery, from connector C139 to C102a, I registered 9 volts, but from the PCM connector (C175a) to C139, it only read 3 volts. There's no resister inline, so I can't explain that one. But I'm not an electrical engineer. The issue for me lied with the connector C102a being faulty. The prongs in the connector were corroded or loose. Wiggling it got it to work for a period, then issues.
View attachment 91105

Thanks for replying! Notice that PCM terminals 47 and 48 are both marked "+ - ". The motor driving the throttle plate must run both directions, so the polarity depends on whether it is opening or closing the throttle. Shop Manual explains it that way, makes sense, DC motors reverse when the polarity is reversed. Notice the dotted coiled line around those two wires, that is shown in the explanations as meaning "shielded", like a coax T-V cable, but these leads are not, but are twisted pairs, like telephone wire. The wheel speed sensor leads are also twisted pairs.

Distance from the Throttle Motor connector to the PCM connector is only about three feet, so if plain No. 18 wire the resistance should be very nearly zero. I'm seeing over 500 ohms for each wire. Tempted to parallel them with wire outside the harness, but fear toasting the PCM. That's why my OP.

On your problem, are you still having trouble? I will look into the connectors you mentioned, see if I can be of any help. I'm very fortunate my old man pushed me to go to DeVry Technical Institute out of high school, and I got a 2-year Electronics degree. imp
 






They'd be designated as 'VREF' if they were voltage sensitive.

Interesting, they are both listed as voltage send and voltage receive (+/-) yet 1835 is listed as motor feed and 1836 as motor ground. So if there is an issue with the motor and it's sending back an incorrect value, that may cause the P-2106.

Though, many of the other parts on that page are a referenced voltage.

I watched this video some time ago, it looks at the different components/causes.

As far as line voltage, or OHMs resistance, I was testing line integrity of my charging system to PCM wire. Using a 9 volt battery, from connector C139 to C102a, I registered 9 volts, but from the PCM connector (C175a) to C139, it only read 3 volts. There's no resister inline, so I can't explain that one. But I'm not an electrical engineer. The issue for me lied with the connector C102a being faulty. The prongs in the connector were corroded or loose. Wiggling it got it to work for a period, then issues.
View attachment 91105

OK, tell me if I got straight on what you did. You disconnected C175 B from the PCM? You wrote C175 A above, connected one terminal of a 9-volt battery to terminal No. 24 in the PCM connector C175B, then put your voltmeter leads on the other battery terminal and terminal 2 in C139, and measured 3 volts? Something's fishy. If you can measure ohms directly between 24 and 2, you should see zero ohms. imp
 






The infinity symbol just means a twisted pair. If it was dashed lines in the shape of a cylinder, then it would be shielded.

I don't think there's an issue running separate wires.

But your resistance is crazy. Testing the wires disconnected certainly shouldn't be showing 500 OHMs. Are you testing at the back of each connector, or through its front? Could be corroded pins.
Does applying a 9v battery get 9v through? I took the 9v power connector out of a Goodwill alarm clock that cost me 1.28. On wires that don't show VREF, I've not had issues doing this.

On my alternator, I spliced in a new connector and it solved my issue.
 






OK, tell me if I got straight on what you did. You disconnected C175 B from the PCM? You wrote C175 A above, connected one terminal of a 9-volt battery to terminal No. 24 in the PCM connector C175B, then put your voltmeter leads on the other battery terminal and terminal 2 in C139, and measured 3 volts? Something's fishy. If you can measure ohms directly between 24 and 2, you should see zero ohms. imp


Sorry, meant C175B. And yes, I got only 3 volts and thought it was fishy too. Being a layman, I realized every time I messed with the connectors, I stopped having charging issues for a month. So I waited for it to occur again, but only messed with one connector (C102A) at the alternator and it fixed it. So I replaced that harness connector and all is good. I can't explain the 3 volt reading.
 






Sorry, meant C175B. And yes, I got only 3 volts and thought it was fishy too. Being a layman, I realized every time I messed with the connectors, I stopped having charging issues for a month. So I waited for it to occur again, but only messed with one connector (C102A) at the alternator and it fixed it. So I replaced that harness connector and all is good. I can't explain the 3 volt reading.

Main thing is, you got the trouble straightened out. It just dawned on me what they're doing: that connection to the alternator has very low current flow, so they probably use a resistance wire which drops about 5 volts leaving 8 or 9 at the alternator (8+5=13, battery voltage). Just a guess. imp
 






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