Is anyone an automotive tech/ mechanic?

aggiebuilder2003

aggiebuilder2003

Joined
Jan 7, 2009
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I hope I have posted this in the right forum, but if not, moderator please forgive me.

I have a 2005 GMC Sierra half ton crew cab. Of late I have been experiencing problems related to the electrical system and speedometer. On occasion, especially if it is dark where the headlights are in use, I get a "strobe" effect where they go slightly dim, then bright, then dim very rapidly. This also takes place throughout the instrument cluster and pretty much everywhere something is lit up. I have also noticed that during normal day driving as well as when described above that the volt meter tends to go from a lower than normal to a higher than normal charge and bounces between the two sometimes for just a few seconds, sometimes the whole drive home. (About an hour)

In regards to the speedometer, most of the time it works fine, but then there are times where it just "gets stuck" for no aparent reason. I drove home on a 65 mph highway the other day and for 30 minutes of the drive it was stuck on 13 mph. I have no idea what is going on and have taken it in to a local shop that is pretty reputable, but no luck diagnosing the problem. The alternator and battery were the prime suspects and while the battery tested bad and was replaced, the alternator tested fine at the time and the mechanic has been unable to reproduce the problems described above. Can anyone help? Thanks in advance!

Chuck
 
I hope I have posted this in the right forum, but if not, moderator please forgive me.

I have a 2005 GMC Sierra half ton crew cab. Of late I have been experiencing problems related to the electrical system and speedometer. On occasion, especially if it is dark where the headlights are in use, I get a "strobe" effect where they go slightly dim, then bright, then dim very rapidly. This also takes place throughout the instrument cluster and pretty much everywhere something is lit up. I have also noticed that during normal day driving as well as when described above that the volt meter tends to go from a lower than normal to a higher than normal charge and bounces between the two sometimes for just a few seconds, sometimes the whole drive home. (About an hour)

In regards to the speedometer, most of the time it works fine, but then there are times where it just "gets stuck" for no aparent reason. I drove home on a 65 mph highway the other day and for 30 minutes of the drive it was stuck on 13 mph. I have no idea what is going on and have taken it in to a local shop that is pretty reputable, but no luck diagnosing the problem. The alternator and battery were the prime suspects and while the battery tested bad and was replaced, the alternator tested fine at the time and the mechanic has been unable to reproduce the problems described above. Can anyone help? Thanks in advance!

Chuck
 
In regards to the speedometer, Alot of Chevy trucks and Tahoes in the last several years have had problems with it sticking as you described.

My work truck, which is a 2004 Silverado, had the same problem. I did a little research on the subject and checked out a few chevy forums and found that this is a common problem. I have no idea if this is true or not (because as we know everything we read on the internet is true) but I heard that if the vehicle has less than 80,000 miles on it Chevy will replace the speedometer cluster panel for free, but if you have over 80,000 miles you're on your own. And I beleive it is about 600 dollars for a new speedometer cluster.

Because my truck is a company owned vehicle I chose to have a new speedometer installed but there is another option which is less expensive. I know this sounds funny, but if you check on Ebay under Chevy Speedometer Cluster, there are people that you can send your cluster to and they will fix it for you for about 100 bucks.

It seems that the problem, has something to do with the plastic gears that are behind the speedometer inside of the cluster.

If you decide to send your cluster off to someone, you can easily remove the cluster yourself. The plastic trim frame around the cluster and radio just pops off with a little pressure. After that all you have to do is remove the four screws that hold the cluster in and unplug the wiring harness and thats it.

Before I did anything I would recommend calling the dealership and asking them if there are any recalls you should know about.( They are not calling this a recall but it seems to be a common problem.) After they answer your questions about the recall, if they dont say anything about the speedometer cluster I would ask them specifically about it.

Good luck and let us know which way you decide to go!!
 
Yeah, I saw the same info. Unfortunately I have almost 100,000 on it. Sorry about the multiple same threads, my computer hung up and it didn't look like it made it on at first. Thanks guys!

Chuck

P.S. No ideas on the headlight thing hunh?
 
Do you have a closed loop charging system? I work mostly on imports but about 25% on domestic. If you do then you need a real tech to go in there and test it, he will have an up to date database and proper equipment to use to figure it out. If I knew the exact problem I would let you know in a heartbeat. All alternators have voltage regulators which are usually located in the alternator case but are also located in the engine computer, especially those with the closed loop systems. If indeed it is an internal problem then most likely you'll need a new engine computer which will then need to be programmed. Could be a bad connection and that itself could even be in the instrument cluster, but it might not. Good luck. ;)

Ya might try having a qualified technician wiggling the connector at the alternator to try to get the lights to blink, be VERY careful doing this as the engine will need to be running, if you are not qualified to do this dangerous test then do not attempt it.

Check battery connections, fuses, cables, and is the bolt for the ground cable securely fastened. If the transmission has ever been removed might wanna look see any loose wires around there. ;)
 
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Ryou,

I'm not sure if I have a closed loop system or not, but from my internet research and from talking to a couple of buddies that have had similar problems with their vehicles, it sounds as if the healight/ power problem is my alternator. In regards to the speedometer, I did some more internet research and it seems GM installed a bunch of junk instrument clusters in a number of their vehicles from 03 to 05. They issued a recall on the 03s and 04s, but with the 05s they would not issue a recall and would only replace them if it occured under 70,000 miles. I called the dealership where I bought the truck to see if something changed and of course, it hasn't. I have 99,000 miles on mine so I'm on my own. $540 bucks to replace the instrument cluster if I choose to. I asked about replacing it on my own, but the odometer info is stored in the cluster, so even if I replaced it myself, I would still have to get them to scan in my information. I looked into having it repaired because there is a local shop that does that work. They wanted $425 to repair it and would only warranty it for a year. Guess I'm going to pay through the nose either way.
 
I don't like to hear things like this, can you go above the dealer to a regional rep on the cluster? Sounds ignorant you can't get the same treatment as a truck a year older same problem. A common strategy is to "outlast" the customer, in other words they grind you down to where you think you have no options. I am not saying you have any options but I would try to write a letter or two if I were you. BBB?
 
I work at a GM dealership, unfortunately.:D

The speedometer is a major problem in GM's full size trucks. The stepper motor that drives the needle for the speedometer is junk... for lack of a better word. This actually is covered under warranty, even if you are out of your 3yr-36,000 mi. factory warranty, GM put out a 7yr.-70,000 mi. warranty on their Instrument Panel Clusters.

As for the lights flickering, I asked our main electrical guy and he suggested what Ryou suggested... the alternator could be bad. One simple thing you can check is your battery, not the battery itself but the connections. Get an 8mm or 5/16 wrench and make sure your battery bolts are tight as possible. You should be able to grab the batt. cable and pull it back and forth without it moving at the battery, at all. Loose connections at the battery are the source of many customer complaints.

Edit: I missed the part where you mentioned you were out of warranty. Replacing the IPC is very easy and requires no diagnostic time... the most I you should see in labor is 1.5hrs.. One can replace the IPC in less than 5 minutes, the only time consuming part is reprogramming it (which takes about 20 minutes). If you have a good repore with a dealership in your area, they may Goodwill it (give you a new one for free even though you are out of warranty), or atleast pick up the labor. One more thing I wanted to add was that I don't remember ever replacing an alternator on a truck similar to yours, so I don't advise just throwing one in there... as there is a very high possibility the problem you described is a wiring issue. Best of luck to you.
 
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The problem could be alot of things, could be a bad diode in the alternator, you may want to do the cluster first and see if that has any effect as there is a charging system circuit located there and the problem from what you have said is hard to reproduce. I agree with GregS to not jump the gun, be patient and research options, the truck does not seem in danger of becoming undriveable so that in itself gives you alot of leeway and in the meantime the problem may get more frequent and thereby easier to track down. ;)

+ there is yet another module which may affect the headlights, called the BCM
 
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GregS and Ryou,

I really appreciate you guys trying to help me out, and Greg, don't feel bad, I still stand by my Sierra 100%. I've just taken it as a fact of life that "they don't make'em like they used to." Since you guys are investing a lot of time in my problem I thought I'd summarize what the course of events has been and maybe it will cause a light bulb to go off for someone and help crack the mystery.

1. The headlight problem first occurred back in December 08/ January 09 when it was cold down here (mid to low 30s at night). At first I thought it was my battery getting ready to die, but it never did and seemed to "go away" after only a couple of occurences so I kept driving as it was. Also at about this time, to the best of my memory, the backlight on the passenger climate controller went out. I have a dual-zone AC.

2. When passing a guy on my way to dinner one night in June of this year the speedometer first "stuck". This didn't recur until here about 3 or 4 weeks ago and as I said, doesn't do it often. Speedometer is slightly "choppy" when accelerating.

3. The headlights again started doing their thing about 3 or 4 weeks ago. This happens more frequently than the speedometer thing and usually happens when I first start the truck in the mornings after it has sat in the driveway all night. AC, headlights, radio all going and the lights start to "blink" while sitting there idling. Starting to drive down the road doesn't seem to worsen it, but doesn't immediately correct it either. Also manifests itself during some night driving. All seems to point to heavy demand on the electrical system because all of the backlighting in the dash, radio controls, AC controls dim with the headlights at the same time and the charging needle falls or spikes with the highs and lows in the dimming lights.

4. I took the battery and alternator to be checked at the local Autozone about the time the headlights began to start their blink again. The battery test came back bad, (was the original battery) their machine did not have the correct settings in the computer to check the alternator. As it would have it neither did the O'reilly across the street. So, I bought a new battery and installed it and reinstalled the alternator. The problem seemed to go away for a week-ish, then came back.

5. Been driving it around since, took it in for its 100,000 mile tune-up two weeks ago, had the shop owner who is a high school friend of my wife check the alternator again, everything checked out. Lights are still blinky at times, hasn't done it in the last few days that I can tell. The charging needle has been a little bouncy though. Goes from reading about 12V to about 15V back and forth for a bit then either stays at 15V or drops to 12V and usually stays put the rest of the way home, about an hour drive. The needle also does this when the headlight thing is happening, I assume it is the same phenomenon just happening during daytime driving.

I think that sums it up to date. Since the lights went on the fritz before the speedometer showed signs of trouble I tend to disagree that the cluster is causing that problem. I didn't think about the AC controller going out at the same time until you guys mentioned the cluster as a possible cause of the power problems. Maybe the AC controller has something to do with it.

You should also know I installed an aftermarket adapter for my iPod as well. I did this work myself and I feel safe in saying that I did not nick any wires or pinch anything when putting this in. The iPod adapter had also been in there a while before this started happening since it was my father's day present the June prior to the first headlight occurance which happened the following December-ish. Thanks again for all your help. Hope this info helps you guys help me figure this thing out.

Chuck
 
Keep what GregS and I have told you in mind, it could be anything and it could be a nasty diag...or not, If it was my truck I would try full fielding, load testing, Vd test, to try to duplicate the symptoms or find some other anomalous activity then pull the schematic and keep poppin away, but since it is your truck after all that was done but I didn't yet kill the gremlin how much would you be willing to pay the diagnostic charges? there really is not many option besides waiting for the problem to stick / getting it to a tech unless someone is parts hanging which I don't do. By the way nobody agreed it was the cluster causing the lighting problem in the first place, although I would not rule it out, but good luck. ;)
 
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car electrical problems are THE WORSE to diagnose...reading the thread from the top, the charging system/calternator was first to mind...and i know about intermittent electrical problems; so even though the alternator initially tested fine, if it was me i would have replaced it at that point anyways...i have been stuck by an alternator going bad before (at night/in snow), it ain't worth it to play "if it ain't (actually) broke, don't fix it"....
 
aggiebuilder2003 said:
It's been a long time, but it turned out to be the alternator.

Chuck
Click to expand...
The alternator has a built-in solid-state regulator, correct? After reading your diagnoses to this point, I was thinkinng this was the culprit. I'll bet it still is. The Alternator (providing power) was working fine. The regulator was intermittent.

Glad it's fixed. :D

Coop
 
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