08 Alpha Cluster Gauge Problems

[video=youtube_share;fgGrRM1p3ek]https://youtu.be/fgGrRM1p3ek[/video]

Problems The ALPHA has...
-Speedometer moves up and down when revving on PARK ----> (car not moving) **SEE VIDEO**
-Sometimes the speedometer don't even work at all causing the transmission not to shift into the next gear (RPM just revs high until I let off the gas pedal)
-Sometimes it will lag (It won't move/work until I hit a certain speed like for example from 0mph-29mph it won't move or work until I reach 30mph then the speedometer will jump up to at 30mph)
-Only stops working on 1st gear

--ALREADY REPLACED--
-Had my transmission rebuilt a few months ago
-New INPUT speed sensor (Goes inside/internal the transmission)
-New OUTPUT speed sensor (Goes outside/external but in the transfer case housing)
-New OUTPUT speed sensor wire connector

**Bad cluster**??
ALSO
**When I replace/took out the old output speed sensor it had diff oil on it, is that normal? Maybe the diff oil cause it to read the mph erratically?

I can’t speak directly to the issue, but make sure the connections are tight, and any ground is solid with lots of surface contact. Still tracing down similar issues with the fuel gauge.

Both the sender and gauge pod were replaced under warranty, problem still exists and so I suspect this is a wiring issue.

Your situation sounds similar.


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Wow, you've had some electrical issues with this vehicle! Especially considering where you are located, Bowser's recommendations of looking at grounds is an especially good one. Maybe other corroded wires. I've had battery cables get rotted out creating weird conditions. But I think you're also looking at transmission issues more than speedo issues. I'm no engineer, but I'm thinking the speedo is controlled by the trans and not the other way around, as you allude to. I would take it back to the transmission shop.

For example, I'm pretty sure it's an electronic speedometer vs. a cable operated speedometer (I am not 100% on this, I've never taken this apart), so the speedo would just be controlled by signals it receives from the computer, which in turn is fed by the transmission. I don't think the speedo sends signals to the computer to send to the trans. That said, maybe there's a computer issues but I'd put my money on the trans rebuild.

Just found out my scangauge II reads 0mph also when the speedometer stops working.
If my scangauge is plugged to the OBD port does that mean I have a issue with the ECU instead then ?
Because if I have a bad speedometer then why does my scangauge also reads 0mph when the H3 is moving/accelerating.
That tells me if the speedometer needle don't work then the digital speed on the scangauge don't work also.
Bad ECU?
Because if the speedometer cluster is bad it shouldn't stop the scangauge digital mph from reading. Correct?

Also replaced a
-New accelerator pedal sensor assembly
-Throttle body position sensor (TPS)
Still having issues

Planning to do a Colorado/Canyon instrument cluster swap next maybe the OEM H3 cluster is just going bad. If that still don't fix the problem then I'll know its probably a ECU or electrical wiring at fault

I would be surprised if the gauge cluster is the cause of your problem. As far as i know it doesn't produce any signals it only displays what the ecm/tcm are sending it through the serial data wire. I think the issue lies in your transmission. Are you sure the transmission isn't slipping? Did all of these issues exist right after the rebuild or did everything work for some period of time and then suddenly they started?

Any codes?




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No codes** Have this issue after the rebuild but alot had happen I fixed alot things that didn't need fixing thats why its causing all these problems. Like the saying 'don't fix it if it ain't broken'

Thats what I thought also if the speedometer only displays then its probably a signal issue thats why the scangauge doesn't read also when the speedometer stops working

I had my transmission rebuilt a few months ago by a family owned business they did it at their home/barn garage shop.

Thoughts I have on this subject; Is the ECM putting the truck in a closed or open loop condition? This truck has an electronic speedo. My '89 K1500 Chev also has an electronic speedo. I realize there is a big difference between the two vehicles but some conditions are similar. The gauge cluster in my '89 is a printed/ soldered circuit board. I've chased down hairline opens in the circuit board and I still have intermittent failure on the speedo as I drive down the road. When the speedo goes to 0 mph as I'm on the highway the engine changes tone and goes in to open loop (limp home mode). I actually give a quick rap on the front of the gauge cluster with my knuckle and the speedo starts registering mph again and the ECM goes in to closed loop with a corresponding sound in the tone of the engine. What I'm saying is the ECM is seeing a signal from the speed sensor on the trans through the speedo to the ECM. This may or may not be the way your Alpha works but it is something to check.

Here is the 08 wiring diagram, search cluster

https://schwarttzy.com/wp-content/uploads/2013/01/Hummer-H3-Wiring-2008-1-4-1.pdf






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alrock said:

Wow, you've had some electrical issues with this vehicle! Especially considering where you are located, Bowser's recommendations of looking at grounds is an especially good one. Maybe other corroded wires. I've had battery cables get rotted out creating weird conditions. But I think you're also looking at transmission issues more than speedo issues. I'm no engineer, but I'm thinking the speedo is controlled by the trans and not the other way around, as you allude to. I would take it back to the transmission shop.

For example, I'm pretty sure it's an electronic speedometer vs. a cable operated speedometer (I am not 100% on this, I've never taken this apart), so the speedo would just be controlled by signals it receives from the computer, which in turn is fed by the transmission. I don't think the speedo sends signals to the computer to send to the trans. That said, maybe there's a computer issues but I'd put my money on the trans rebuild.

Click to expand...

The H3 was from Fort Worth, Texas and was used for off roading just pick it up on September 2020

This is from the guy who rebuilt my transmission his exact words.
"You could have a bad wire harness. Could be something wrong in the transfer case possibly getting a bad read from from the Reluctor ring in the transfer case. There is nothing in that transmission that would affect your speedometer working but if you have something faulty in the speedometer system it will affect the transmission from shifting. With it being intermittent I would suggest a bad wire somewhere in the harness from the speed sensor to the ECU."

This probably won't change anything, but have you unhooked your battery cables and tied them together overnight just to see if draining the PCM would 'reset' it? I would double-check the connector pins down around the transmission in case one got bent or broken during the tranny work.

I doubt if it's your cluster too. I'd be checking connector pins in the tranny area. If you know someone who has a decent scanner like a Snap-On scanner, you can perform a 'gauge sweep' before removing the cluster, and/or hold the needles at full position to test them.

I've had my cluster apart (right down to the bare circuit board). There isn't much in there other than a microprocessor and a number of surface-mount devices and LEDs. It gets its signal from the PCM. Once ya get the clear lens off, you pull the needles off (carefully) and remove the black layer that has the speedo and gauge numbers on it. That reveals the circuit board. The needle motors are like miniature dc brushless motors as best as I can tell. They don't have a 'stop' to them as I recall. When yer finished, you pop the needles back on (they will re-center themselves when you turn on the ignition). You might pull the cluster and carefully at the connector going to the cluster as well. It takes 5 minutes to get the cluster out. You literally pull the plastic bezel in front of the cluster off with your bare hands, then 4 small bolts to remove the cluster, then pull out. That's it.

You can get the wiring diagrams at Schwartzy.com ...if I remember right. Might not be for your yr, I'm not sure, but should be similar i would think

@ Jeepwalker
My H3 has a PCM/TCM tuned because it got cams If I unplug my battery and tied the cables together will that reset my tune to factory?

What kind of tuning system? Was it software dropped into the PCM? W/o knowing the details I guess I can't say for sure. I doubt it but....

Previous owner cammed the Alpha engine and said it was tuned. Right now its running on premium gasoline I'm sure it has something to do with the PCM or TCM tuning. I also can go past 100mph, it doesn't have that mph lock, but my previous 2010 GMC Sierra Denali 6.2L V8 locks at around 90mph or something.

If I just drive normal my H3 tranny shifts at 2000rpm into the next gear I feel like that's not factory but that's actually good, it can save some mpg's...

I did a cluster swap and it did not fix the problem. Same o dead speedometer sometimes don't work, but will work...
That tells me it probably has something to do with the PCM or TCM or ECU or maybe even the speed sensor wire...
****I did run a Pedal Commander but recently I just took it off, do yall think it can mess anything else up??****
Was told not to switch modes on the fly/driving which i did sometimes but it was supposed to be on a dead stop to switch between the modes ECO_CITY_SPORT_SPORT+

Whats next to check you all?

I would think if you had a sensor dropping out you'd be getting service engine codes, even 'soft' codes. Have you checked to see if you have any 'soft codes'? If you know someone with a good scanner, like a Snap-on or TechII, where you can dig into the real-time readings, perhaps you can observe sensor readings while a partner is driving. I'm trying to remember, but I think the sensor outputs on a scanner are going to be what the PCM is interpreting (not the actual output from the sensor). But still, if the PCM was receiving flakey readings, that would be a place to start.

Or reset the PCM. I doubt the updates would disappear if the pcm is updated. When you update the software, you're re-programming the PCM. ...but verify that with whoever you got the update from, I'm just assuming it will stay in there. Could be buggy software too (??)