Instrument cluster, intermittent issue with gauges not working

K.KILGORE

MEMBER
2001 GMC SIERRA
4.3L
V6
2WD
AUTOMATIC
163,600 MILES

New to me truck purchases 3 days ago.

The truck listed above is a 2WD step-side with a tilt steering column.

The headlight switch needs to be replaced. When turning on, you have to turn back just a tough to get headlights to come on. The auto on and off works just fine.

The frame is in excellent condition. That is the reason I bought the truck. The previous owner told me of the issue. Said issue would go months and not happen. Then maybe act up for a few days. Then wait months before it happens again.

It has an intermittent issue with gauges not working. The fuel, temperature, oil pressure, and tachometer will bounce or completely stop working.

Haven't been driving when this happens. So don't know if the speedometer is affected. The check engine light is on, but I haven't had a chance to have codes read. Waiting until I get it transferred in my name before driving. Just moving around in driveway to mow and move my boat around.

The message center shows not charging but voltmeter shows charging.

I'm thinking it is a ground issue but don't know where to look or the ground points.

FWIW. I have a 2000 Blazer with a 4.3L with a bad frame that I can take parts off of if needed. That is how I plan to repair the headlight switch.

5 Replies

JACOBANDNICKOLAS

MECHANIC
108,269 POSTS

Hi,

The instrument clusters in the GM trucks during this time period are known to fail and need to be rebuilt. What you described sounds like that is the case. The solder joints fail internally on the printed circuit boards. As a result, the gauges act a bit crazy.

As far as the charging, I attached the wiring schematic below for the charging circuits. Take a look through them.

Also, let me know how you determine the alternator is producing.

I will watch for your reply.

Take care,

Joe

See pics below. Note: I had to cut the schematic in half to make it readable. I did overlap them so you can follow from one to the next.

Images (Click to make bigger)

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Sunday, April 24th, 2022 AT 7:38 PM

K.KILGORE

MEMBER
3 POSTS

Thank you for the reply and the information.

I was just going off the intermittent instrument cluster to determine if the truck was charging. When the gauges are acting normal the volt gauge does show charging and the message center is blank.

I'll use a multi meter to verify the alternator is in fact charging the battery.

I'll report back what I find out. It will take a while. I'm out of town this week.

Again, thank you.

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Monday, April 25th, 2022 AT 10:49 AM

JACOBANDNICKOLAS

MECHANIC
108,269 POSTS

Hi,

I look forward to hearing what you find. Hopefully, it is something simple. As far as the alternator test, I don't know if you need it, but here is a link that explains how to perform the test:

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

Let me know what you find and have a safe trip home.

Joe

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Monday, April 25th, 2022 AT 6:17 PM

K.KILGORE

MEMBER
3 POSTS

Thanks for the alternator test article.

I used a nylon wheel on a drill to clean the stud and lug on firewall used by ground strap. And the stud and lug for the engine bay light on hood. Then applied dielectric grease before reassembly.

I cleaned the side post battery cables the same way with bolts removed and applied dielectric grease there also.

Used the diagrams you provided and determined pin A8 (ground) going to the instrument cluster now has 1 OHM short to the metal in steering column, key switch, and door nuts. This was after cleaning the firewall ground location. So, I don't know what it was before.

The headlight switch from the blazer wouldn't work as a donor. Since blazer switch was made with a place for fog lights. Which the Sierra doesn't have. So, I took the existing switch out of Sierra, disassembled, stretched a little spring for the contacts. I applied some more dielectric grease and reassembled. Switch works as it should.

Using multi-meter, determined the battery had 11.98 DC volts. (Was playing radio while working on it) Started truck and gauges worked as they should. Message center was blank. Just had a service engine soon light on. So, I still need to get the codes read.

With the engine idle and at 1,500 RPMs, alternator was putting 14.25 DC volts at battery with headlights, blower, and radio on. Switched meter over to AC and had 0.33 AC volts at battery at 1000 RPM.

I'll keep a check on everything and report back to this question if anything new develops. I don't know if the gauge issue is resolved or if a replacement is in my future.

I only drive this truck on weekends, taking a boat to the lake and such. So, it may be a while before any issues raise their ugly head.

Thank you again for all your help.

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Saturday, April 30th, 2022 AT 7:29 PM

JACOBANDNICKOLAS

MECHANIC
108,269 POSTS

Hi,

You are very welcome. I'm glad to know you got things taken care of.

Please feel free to come back anytime in the future. You are always welcome here.

Take care,

Joe