RPM and Speedo needle fluttering - Chevy Colorado & GMC Canyon
 
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post #1 of 9 (permalink) Old 10-19-2015, 10:12 AM Thread Starter
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RPM and Speedo needle fluttering

Any else notice this? At steady speeds, the tach needle steadily moves up and down a little bit, the speedo does it, but it doesn't jump as far.

It seems like a nit pick, but it's getting to the point where it seems like some one is waving an orange flag at me while im driving.

90% of my driving is at night, so it may make it seem worse with the back lighting.

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post #2 of 9 (permalink) Old 10-19-2015, 10:22 AM
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My tachometer barely moves without an input from me like stomping on the gas or the brake. Similar for the speedometer.

Are you driving at a speed where the transmission is hunting for a gear?

Couple of things to see if it affects the movement:

1. Try same drive in TOW/HAUL mode and see if that reduces the flutter.

2. Repeat same drive in manual mode, and keep the transmission limited to no higher than 3rd or 4th gear.

If some of these things reduce the flutter, then sounds like you are hunting for a gear to much. If no impact to the fluctuations, then probably is some sort of electrical issue. SavageBob probably understands the operation of the speedometer and tachometer better than most, definitely better than I. He may have some other thoughts.

When I watch my two meters, it appears that there is some sort of dampening built into the electrical circuitry. In old days when the transistor was a new fangled device, I would have suggested that my truck has a capacitor in the circuit for dampening purposes.

When you look at the speedometer, does the digital speedometer fluctuate as much as the analog device?

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post #3 of 9 (permalink) Old 10-19-2015, 10:34 AM
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I know mechanical speedos can fluctuate due to a few different reasons. I have never seen a modern electronic speedo/tach fluctuate personally and to me would indicated something electrical. Never seen my colorado gauges do that before.


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post #4 of 9 (permalink) Old 10-19-2015, 11:10 PM Thread Starter
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This is with the cruise set, not accelerating. Semi flat road at 60mph, flutters like a butterfly.

I love electrical problems. My "infotainment system" froze as well, didn't want to waste internet space on that.

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post #5 of 9 (permalink) Old 10-19-2015, 11:33 PM
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The throttle position is still changing although cruise control is set. Any deviation such as wind or grade or just because will force a throttle position change. Granted I suspect it would require noticeable movement before the tach would fluctuate. And speed should be very stable.


Any chance you have electronics that are interfering with the electrical system?
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post #6 of 9 (permalink) Old 10-20-2015, 09:37 AM
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Quote:
Originally Posted by 08Canyon View Post
The throttle position is still changing although cruise control is set. Any deviation such as wind or grade or just because will force a throttle position change. Granted I suspect it would require noticeable movement before the tach would fluctuate. And speed should be very stable.


Any chance you have electronics that are interfering with the electrical system?
I vote for some sort of electrical problem.

The throttle position can change all it wants. If you are doing 60 MPH steady on the highway and maintaining a steady overdrive gear like 5th or 6th, really should be 6th in the scenario described, then the engine is locked in with the transmission. If tire rotates at a certain RPM, the engine should be rotating at the appropriate RPM given the complete power train gear ratio. Only way that changes is with transmission slippage or gear change.

It could be caused by transmission hunting for a gear, but I think that would really transmit to the whole truck in vibration based on what is being described. I think the gear hunting would catch your attention more than a fluttering tach/speedometer.

Make sure it is reproducible and then take a service tech for a ride and show them. While I would tend to shy away from electronics interfering, unless you have done some major projects to your truck electrically, would put my bets on a loose connection or else a bad BCM or some other black box on the truck. A local service tech figuring out an interference issue will be a long shot. (As they are mostly just parts changers, innovative thinking is not in their toolboxes usually.)

Someone on a different thread suggested that speed is no longer taken from the transmission but from the ABS wheel sensors. Bad sensor, bad connection, etc. in that area? Dirty rotor, broken tooth on the rotor that causes unusual reading?

This seems to be a one of a kind problem, so unless the mechanic has seen it before or GM has seen it on other vehicles and issued a service bulletin, resolving it may be a long diagnostic headache.

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Last edited by CaryBosse; 10-20-2015 at 09:45 AM.
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post #7 of 9 (permalink) Old 04-21-2017, 07:31 AM
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Quote:
Originally Posted by wildwest450 View Post
Any else notice this? At steady speeds, the tach needle steadily moves up and down a little bit, the speedo does it, but it doesn't jump as far.

It seems like a nit pick, but it's getting to the point where it seems like some one is waving an orange flag at me while im driving.

90% of my driving is at night, so it may make it seem worse with the back lighting.

I know this thread is an older one but I just searched and found it. I bought a Canyon just last month. It's been in for service 3 times the first 500 miles. The problem was finally determined that the module in the dash was bad for the DIC. The entire instrument cluster was replaced with a new one. I didn't get to drive the truck much the first 3 weeks due the vehicle being in the shop more than it was in my possession. Now that I have drove the the truck a few times I have noticed the same exact thing with mine. Speed and tach flutters just a little. This is still a new truck with approx 800 miles. Did you have any resolution with this issue of was it determined to be "normal"?
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post #8 of 9 (permalink) Old 04-21-2017, 03:50 PM Thread Starter
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Originally Posted by mmdavidson0128 View Post
I know this thread is an older one but I just searched and found it. I bought a Canyon just last month. It's been in for service 3 times the first 500 miles. The problem was finally determined that the module in the dash was bad for the DIC. The entire instrument cluster was replaced with a new one. I didn't get to drive the truck much the first 3 weeks due the vehicle being in the shop more than it was in my possession. Now that I have drove the the truck a few times I have noticed the same exact thing with mine. Speed and tach flutters just a little. This is still a new truck with approx 800 miles. Did you have any resolution with this issue of was it determined to be "normal"?
I actually just got used to it, never took it in.

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post #9 of 9 (permalink) Old 04-21-2017, 04:28 PM
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I have seen an In-line filter that flattens out the electrical signal to the gauges. The last I saw was on a Buick Grand National. but I bet they are still used. I think I can send you a wiring diagram for your colorado.
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