App Circuit 04 Tahoe

Joe Owner/Technician Benicia, California Posted   Latest  
Question
Electrical
2004 Chevrolet Tahoe LS 5.3L (T LM7) 4-spd (4L60-E)
P1125

Trying to find out if its normal operation. Doing testing on the app sensor and found the app1 portion of the sensor assembly has a 5v ref, good ground and a normal signal. App2 however, has a signal wire that looks like a 5v square wave. Tested the 5v ref supply from the tac module and it also looks like a square wave. Info on alldata shows these just being a potentiometer. Just havent seen this before is this normal?

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Stephen Technician
Gallatin, Tennessee
Stephen Default
 

I think it’s normal. I’m don’t recall the exact year but I have seen that pulse on two other chevy trucks, both 6.L. Two is all that I have tested. One had a fault the other truck didn’t and was only for comparison. I wouldn’t have called it a square wave, more of a regular timed pulse, low IIRC.

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Robert Diagnostician
Ballston, New York
Robert Default
 

Yes that is normal. It is a common practice among many manufacturers for circuit integrity.

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Joe Owner/Technician
Benicia, California
Joe Default
 

Here’s the pic of the 5v ref supply for the app2... sorry about the quality I’ll figure out getting pics on here from the scope tonight. I appreciate the help guys

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Geoff Diagnostician
Lahaina, Hawaii
Geoff Default
 

I have heard that referred to as the "diagnostic pulse" and it is visible on many different APP circuits, that I have seen captures of, over the past few years.

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Joe Owner/Technician
Benicia, California
Joe Default
 

Weird that both don’t do it , just my opinion I guess

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Robert Diagnostician
Ballston, New York
Robert Default
 

From what I understand it only needs to happen on one of them to prevent noise in the circuit and to verify circuit integrity. I know I have seen it quite a few times with the scope. Like you the first time threw me for a loop but I wrote it off because it is so repetitive it pretty much has to be generated by the module.

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Joe Owner/Technician
Benicia, California
Joe Default
 

Makes sense, appreciate the info!

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Jeffrey Manager
Yuma, Arizona
Jeffrey Default
 

An upload of your scope capture would be cool if you care to share. What you're probably seeing is the controller periodically pulling the voltage down to verify it's not shorted to power. It is normal (if that's what you're seeing) and is filtered out of the data stream, it's purpose is for circuit fault detection.

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Joe Owner/Technician
Benicia, California
Joe Default
 

Not a great pic but just posted one above

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Automotive Owner
San Diego, California
Automotive Default
 

Here's a capture from an 04 Colorado 3.5L, including the ATS BIN file for replay.

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Randy Diagnostician
Glendora, California
Randy Default
 

cool capture

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Joel Diagnostician
Soquel, California
Joel Default
   

it is normal I have a capture save some where . on mine app 1 and app 2 are digital,analog

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