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Wife's car had both RED and YELLOW brake lights coming on briefly occasionally (2006 60k miles). I cleaned up chassis grounds. No trouble for months. Light came back briefly again. Wife remembered I just bought a $300+ scanner and said, "Why don't you use the new toy?" Checked codes: ABS control module voltage out of range and GEM voltage out of range (B codes). IN essence, battery provided <9V or >19V for several seconds.

I decided to tackle "GEM voltage out of range" because "ABS voltage out of range" was more involved. According to factory service manual, @idling, voltage drop has to be less than 100 mV between
1) alternator output post and battery+
2) alternator casing and battery-.

1) was 100 mV. Cleaned up the bolt/nut/washer and applied electrical grease. 1) dropped to 50 mV. Hopefully, it fixed both "voltage out of range" codes.

Assuming alternator output current @ idle 1A, 100 mV drop=0.1 ohm resistance. When alternator current peaks to 50A, voltage drop increases to 0.1 ohm x 50A = 5V. I knew about cleaning/lubing chassis grounds but not about alternator post. I previously did the B+ connections at power distribution panel.

FYI: Please do not misread my post. Pay attention to all brake warnings. I checked fluid, contacts, new fuse, proper functioning of brake, and also took the car to the dealer. They just changed me $120 for diagnostic run, without actually following through diagnostic procedures clearly printed in their own factory service manual.
 

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Even 0.05 ohm is too much.
I will have to redo mine this weekend since my 14 month old alternator blew yesterday. Limited lifetime warranty, but replacing it is not fun. And "limited" means no labor pay.

BTW, how much you have between the alternator enclosure and the battery minus?
 

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Wife's car had both RED and YELLOW brake lights coming on briefly occasionally (2006 60k miles). I cleaned up chassis grounds. No trouble for months. Light came back briefly again. Wife remembered I just bought a $300+ scanner and said, "Why don't you use the new toy?" Checked codes: ABS control module voltage out of range and GEM voltage out of range (B codes). IN essence, battery provided <9V or >19V for several seconds.

I decided to tackle "GEM voltage out of range" because "ABS voltage out of range" was more involved. According to factory service manual, @idling, voltage drop has to be less than 100 mV between
1) alternator output post and battery+
2) alternator casing and battery-.

1) was 100 mV. Cleaned up the bolt/nut/washer and applied electrical grease. 1) dropped to 50 mV. Hopefully, it fixed both "voltage out of range" codes.

Assuming alternator output current @ idle 1A, 100 mV drop=0.1 ohm resistance. When alternator current peaks to 50A, voltage drop increases to 0.1 ohm x 50A = 5V. I knew about cleaning/lubing chassis grounds but not about alternator post. I previously did the B+ connections at power distribution panel.

FYI: Please do not misread my post. Pay attention to all brake warnings. I checked fluid, contacts, new fuse, proper functioning of brake, and also took the car to the dealer. They just changed me $120 for diagnostic run, without actually following through diagnostic procedures clearly printed in their own factory service manual.
I'll repeat "old school" V drop test.

I have a copy in a word doc so I will copy and paste.

You need a digital Voltmeter with pointed probes. Use a MV range 200 to 500, you do not need a high-end meter, cheap one is OK. Turn key on, but not start, headlights on high, blower on high. This loads the battery cables up to a high load. Measure voltage from pos battery post to other end of cable, which will likely be the bolt in the fuse box. This bridges from post to screw to see if anywhere along the line there is a weakness. Do the same for ground post to engine block, and also to the body. Should be 100 millivolts or less and steady. Now, you might logically think that there would be little loss to the engine block as it is not under any serious load and the big ground cable. But, there is a secondary ground strap from the body to the engine near the firewall so the load is split between the two ground cables from the battery. Key is, 100mv or less and steady.

Now, turn the lights and blower off. Start the engine. Alternator should be charging hard as you have used up some of the battery topoff voltage. Measure from the ground post of the battery to the alternator housing. You are checking the ground from that to the engine block and more. Again 100 MV or less. If your alternator is accessible, measure from the big screw, output of the alternator to the positive battery post. This checks the integrity of the large wire from the alternator to the battery. In this case 200mv or less.
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Now consider, if the alt is puttin out 30A = charging hard as battery has been drawn down some, then 200MA = 0.007 ohms.

Now this would be a good practice once a year. Problem is doing the alt post on the DOHC. Hard to get to.

-chart-
 

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Problem is doing the alt post on the DOHC. Hard to get to.
Haha, tell me about it :D. I will be fighting that stupid post tommorow morning.
 

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Haha, tell me about it :D. I will be fighting that stupid post tommorow morning.
Hey, just take the tire off and inner fender off and there it is. :lol2:

Of course the alternator is quite another issue.

Good luck with that one.

Likely not of help but, I only did one, and that on a '98 and I was really close to taking it out through the wheel well. Close does not help. I took the pulley off with impact gun and it wiggled right out. I remember because I as so glad I had an electric impact. That alt had a bad bearing. I replaced it and put it back.

-chart-
 

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Discussion Starter · #7 ·
Thanks, chart...
I like your 0.2V approach better. One minor adjustment. Car alternators don't make 30A @idling, not even 10A.
 

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^^^^^ Yup, modern alts like the Ford 3G, 4G, etc produce lots of output amps at idle. The alts of the 1960s produced very little output at low shaft RPMs.
 

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I took the pulley off with impact gun and it wiggled right out.
Last time I managed to pull it out with just the steering knuckle out. Really tight, almost nicked the CV booth.
Today and tommorow looks like raining thou. And my garrage is full with other crap :(

Back to alternators - the alternators will output someting like "all or nothing" cycling the voltage on battery some 0.1-0.2V - with the current set by the battery size and what consumers are "on" at thet moment.
 

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Alt Output

^^^^^ Yup, modern alts like the Ford 3G, 4G, etc produce lots of output amps at idle. The alts of the 1960s produced very little output at low shaft RPMs.
Alt output, idle, in gear in Pic attached.
'01 DOHC.

Fortunately, pic is worth a thousand words, and data trumps opinion.

And I am the proud owner of this little "clamp on".:wub:

Anyway, idle, in gear, and sfter lights on hi and blower on hi for a few mintues with engine off. In this case, the bat chaget topoff has been used and charging system is adding it back. When I turned on the lights and blower it did not change telling me it was running at max for the rpm.

And remember, this is NOT the same as charge going into the battery as a car ampmeter would show. Some of this charge is going into the battery, rest going to the car operating things.

My Lin Intech turns the alt ~50% faster than the Sable, same alt, just mounted different. Appatently the alt is happy being run that fast, as they give nearly no problems. I measured the pulleys to get that ~50% value. That is part of the price for redundant lighting.

Happy charging.

ps It's cold out and this old coot hand do not take it. My excuse for mis typing.

-chart-
 

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Discussion Starter · #12 ·
I stand corrected. I was living one generation back. Thanks for reminding me of my age.
 

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Dang , that's a '70's over the wire ammeter.
Thanks for reminding me how old I am.....
 

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My Lin Intech turns the alt ~50% faster than the Sable, same alt, just mounted different. Appatently the alt is happy being run that fast, as they give nearly no problems. I measured the pulleys to get that ~50% value. That is part of the price for redundant lighting.
No, the Ford designer knows the the Lincoln drivers usually don't "push" the engine all the way up to 6500 rpm like the Taurus ones, so faster pulleys are OK for them. Profiling :p
Same trick on Taurus would end up damaging the bearings due to lead footed owners. I read that you did find out that by experience :)
 
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