ABS Reference Voltage

Carl Technician Texas Posted   Latest   Edited  
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Braking
2008 Chevrolet Silverado 1500 5.3L 4-spd

i found out thru much digging a little info on abs. i had no reference voltage for both front sensors. so looked up tsb's and did not find anything at first. but digging deeper and thru different channels i found this #PIT4683F: ADDITIONAL WHEEL SPEED SENSOR DIAGNOSTICS (JUL 31, 2012) the abs module disables the 12 volt reference when it has determined a problem.

yikes.......It does however provide a 12v pulse on key on... the bulletin goes on to state after having performed the dtc diagnostics and before replacing pcm perform this bulletin.... our job almost requires more of being a research technician than auto technician these days...

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Caleb Diagnostician
Indiana
Caleb Default
 

Yep this is true. But it's not that big of a deal. Just put a PICO on the circuit and capture it when turning the key on. You will catch the module doing its self test.

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Gerald Owner/Technician
Missouri
Gerald Default
 

And you have to cycle the key for it to self test again. It will not reset by clearing the codes from the module

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Tim Mechanic
Arkansas
Tim Default
 

Great information Carl! Thanks! I have this exact truck so it may come in handy for me. 😁

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Gary Owner/Technician
Colorado
Gary Default
 

ikes.......our job almost requires more of being a research technician than auto technician these days. We also have to include this "learning time" into our labor rates because it's becoming a constant issue. Sometimes I spend an hour or more researching a problem that I fix in just a few minutes, so the cost has to be recovered somewhere. The days of the old mechanic who used to carry all…

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Matthew Mobile Technician
Illinois
Matthew Default
 

Yes, this is also a great example of why some of the "traditional" testing methods will fail techs. Current measuring resistors in circuits, circuity self tests, etc. will shut down voltages and drivers to protect the module. Some testing techniques can lead a tech to believe that there is a fault in the module, when it is a fault in the testing process.

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Caleb Diagnostician
Indiana
Caleb Default
 

Exactly Matt, and more often than not this seems too outrage more techs than it should. Why would I want too use a meter when I can quickly get the entire picture on the scope?? Why guess with a meter? As far as I am concerned you have too be smarter too use a meter than a scope lol. Oh well.

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Troy Owner/Technician
Washington
Troy Default
 

so my favorite reply when some one asked how much to diagnose there check engine light or what ever tell them to give me an hour and then regroup it may be figured out but it may just be a direction, they will say I can get it done for free at the other shops and yes they may but I dont work for free ! and these folks think that they can get a code read and diaged for free and most shops that do…

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