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Volt gauge and oil pressure gauge fluttering

Tiny
HEATH01
  • MEMBER
  • 2002 CHEVROLET AVALANCHE
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 220,000 MILES
Just notice the volt and oil pressure gauges are fluttering more at idle than at driving speed. The battery is a 42 month AC Delco installed in 2017 and the alternator is 2018 vintage. I checked connections, all seem to be tight. Any ideas what is causing this?
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Monday, August 30th, 2021 AT 1:55 PM

11 Replies

Tiny
SQM
  • MECHANIC
  • 6,383 POSTS
Hello,

It sounds like the stepper motor for those gauges are getting weak. Each of those gauges has stepper motor that receives the signal from the ECM and displays the value.
If those motor goes bad the gauge will read incorrectly.
Those stepper motors are a fairly common issue for these Chevy trucks and SUVs.
First you need to check and verify the out put of those gauges, that way you know that the issue is the gauge and not other component.
You can check the voltage output to the battery. With the engine running check the voltage to the battery. If its holding steady then it is the gauge. If it is fluctuating then you could have an issue with the alternator.

Here is a helpful video of how to do that test:

https://youtu.be/Z-p4dMJUpUw

https://www.2carpros.com/articles/how-to-check-a-car-alternator

Let me know what you find.
Thank you.
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Tuesday, August 31st, 2021 AT 7:57 AM
Tiny
HEATH01
  • MEMBER
  • 16 POSTS
SQM,

I did the voltage checks, all were good except the AC check had 25 volts. I decided to replace the alternator with a new not rebuilt one, and the battery and belts since all were about 4 years old. I did a quick check on new battery while idling for AC voltage and got 30 volts. Hmmm, that doesn't seem correct. Any ideas why that is? I haven't driven it yet to check if the gauges are still fluttering but at idle they seem okay.
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Wednesday, September 8th, 2021 AT 2:46 PM
Tiny
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Have got a chance to test the voltage in DC?
At the battery, these trucks should have around 14 -15 volt DC with the engine running.
30 AC voltage is about 19 DC volt. Which is high.
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Wednesday, September 8th, 2021 AT 6:15 PM
Tiny
HEATH01
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Yes, I checked the DC voltage it is 14.6 with A/C on, fan on full, lights were on. So what is causing the high A/C reading?
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Thursday, September 9th, 2021 AT 12:45 PM
Tiny
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  • 6,383 POSTS
Well, as far as the vehicles system is concern as long as the DC voltage is in that range, everything will work just fine.
Even though the calculation from AC to DC makes it seems high, given the nature of the two currents, in a 12V electrical system it calculates differently and the output checks out.
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Thursday, September 9th, 2021 AT 8:06 PM
Tiny
HEATH01
  • MEMBER
  • 16 POSTS
So, is there any issue with shortening battery life because of the AC voltage? Or is it possible the voltmeter is not very accurate?
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Friday, September 10th, 2021 AT 12:51 PM
Tiny
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It's more likely that the calibration on the voltmeter is off.
As your are getting the correct amount of output from the alternator to the battery. So that will not impact the battery life.
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Friday, September 10th, 2021 AT 12:53 PM
Tiny
HEATH01
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Okay, thanks for the help.
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Friday, September 10th, 2021 AT 1:01 PM
Tiny
SQM
  • MECHANIC
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You're welcome.
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Friday, September 10th, 2021 AT 1:15 PM
Tiny
HEATH01
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  • 16 POSTS
SQM,

So, my meter was off on AC voltage. I had everything checked at my mechanic, grounds, voltage etc. Today I put in the new battery and now my speedometer read 100 MPH and stays there. What did I do?
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Sunday, October 3rd, 2021 AT 12:06 PM
Tiny
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When you turn on the key, does the speedometer move at all? Or is it stuck at all the way to right all the time?
It is strange but you could have a bad stepper motor (that controls the speedometer).
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Tuesday, October 5th, 2021 AT 7:06 AM

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