Maybe I just never noticed before but last night that the dash instrument panel lights seem to be flickering a bit. Played around with it today by cleaning up some ground connections although I couldn't get to all of them, but no change. The problem seems to be only with the AC on and the headlights on. I looked through some old posts about the issue affecting the headlights too, but I can't see any problem with the headlights flickering. I'm not exactly sure what to check next. The alternator is fairly new - about 4 months and I've had that tested and it came out fine. The battery is also new - changed about 2 weeks ago. Does anyone have any suggestions on what to try next? I appreciate any thoughts.
Flickering dash lights and courtesy lights on '04 Envoy
- Thread starter jimmackey11
- Start date
Have you found the couple of threads that discuss where all the grounds are, especially the one for the dash area on the right side of the transmission hump at the bottom of the radio stack?
Does the voltmeter on the dash wiggle at all? If not, that's good because the gauge is driven by a data message from the PCM.
In general, dash lamps are on a dimmable bus, so a flaky dash light adjustment wheel, or a flaky power or ground connection to the the BCM at the rear fuse block could be the root cause. Or a flaky Megafuse connection up front.
Does the voltmeter on the dash wiggle at all? If not, that's good because the gauge is driven by a data message from the PCM.
In general, dash lamps are on a dimmable bus, so a flaky dash light adjustment wheel, or a flaky power or ground connection to the the BCM at the rear fuse block could be the root cause. Or a flaky Megafuse connection up front.
I've only seen the ones with the engine area grounds not the ones in the dash area by the transmission hump. For your question about the voltmeter on the dash gauge I haven't tried that - I'd have to locate that too as to where exactly to test it. A bit - large bit - of a newb testing electrical grounds and things like that.
OK - checked out the ground cluster on the side of the transmission hump and nothing registering there, so good news on that! Checked out the rear fuse block and a couple more ground connections in the engine area and everything seems OK but I cleaned everything up just in case. So no bad news so far but the mystery continues....
I had the battery, alternator, and starter all checked out today just to be sure and all came back awesome. So, does anyone have any more suggestions as to what the problem could be now? I also have some flickering in the courtesy lights. All of this when the AC is on - not noticeable with the AC off.
Is the voltmeter dash gauge needle steady during all this? Did you check the connections to the rear fuse block and BCM?
The dash voltmeter is pretty steady at about 14.3 volts - occasionally only a very minute drop to maybe 14.1 volts but never below that. I checked what I could see at the rear fuse block. I was looking for any diagrams or pictures of what to check and what you can take apart there. I was nervous to remove the 4 nuts that seem to attach it to the floor without getting some confirmation. I can only imagine the trouble it could cause to disassemble this incorrectly! For the main power and bundles that lead into this area everything looked clean and tight. What steps or connections should I do exactly? Any guides or previous threads that would be helpful?
On the drive home tonight pretty much the same story - flickering courtesy lights, dash lights with the AC on.
Don't disassemble it, but I would take a socket (carefully) to the red wire connection. That's the feed from the 125A megafuse up front. Also check the megafuse screws up front. If the dash gauge meter looks OK without drooping, then I'd suspect the PCM is getting a good steady voltage.
Wait a second.......while you're driving, the RPM is not down at 600 RPM where it is for idle. It's up at driving speed. So when the AC cycles on and off the alternator is spinning nicely and the only change is the mechanical load of the compressor being added to the serpentine belt.
How old and in what condition is your belt?
How old and in what condition is your belt?
the roadie said:
Anything on the megafuse connection other than just checking and maybe cleaning the screws up a bit that I should be looking for?
Nothing other than make sure they're tight and no oxidation. It would be very useful if you could bring wires from there back into the cabin so you could check with a handheld meter during a droopage event. Very hard to figure out what you're seeing without slapping a real meter on one of the flickering lights. When you mean courtesy lights do you mean the reading lights or a visor mirror light? You could put a meter on those and have somebody read it while you drive and observe the droopage.
Lots of "observations", maybe a bit more qualifications may help. So "things happen when the AC is", OK. So if you just let your vehicle sit in park running in the driveway, do you notice the "flicker"? Next, if you do, carefully have a second set of hands go around "nudging" things to see if they can find a "connection issue". Next, if you don't have the issue in park, next try in gear with the brake on (firmly). Do you get "flicker". Again, have the second set of hands nudge things and observe. As roadie asked what is your idle engine speed in park and in gear???
Vicompc
Member
- Dec 5, 2011
- 109
I had the same problem with mine, but the headlights flickered along with the interior and dash lights. When I would watch the gauge it looked normal
. I also took the altenator in and had it tested on truck and it came back normal. This went on for almost 6 months and I couldn't figure out what was causing it, I finally took the altenator off the truck and took it in to be bench tested. What was interesting is on the truck it tested fine but on the bench test under load you could see the fluctations. I replaced the altenator and have not had the problem since.
BTW I also tightened up every gorund on the truck while trying to figure this one out and chcecked the headlight switch.
. I also took the altenator in and had it tested on truck and it came back normal. This went on for almost 6 months and I couldn't figure out what was causing it, I finally took the altenator off the truck and took it in to be bench tested. What was interesting is on the truck it tested fine but on the bench test under load you could see the fluctations. I replaced the altenator and have not had the problem since. BTW I also tightened up every gorund on the truck while trying to figure this one out and chcecked the headlight switch.
Oh, just a hint to anyone ever reading this thread....the main current for our headlights doesn't go through the switch like older vehicles did. All the switch does is control relays (by way of the BCM and PCM and the front fuse block). So a dirty switch may fail to turn them on, but if it operates at all, and the lights are still flickering or flaky, the root cause has to be somewhere other than the switch. Might save somebody time someday. 
budwich said:Lots of "observations", maybe a bit more qualifications may help. So "things happen when the AC is", OK. So if you just let your vehicle sit in park running in the driveway, do you notice the "flicker"?
I notice the flicker while driving and while in park in the driveway
With the Envoy in park, AC on & lights on, yes there is a flicker. Readings from the multi meter:
Battery - 13.83-13.85; Courtesy or reading light connector - 13.29-13.36; RPMs - slightly above 500
With the Envoy in the driveway in gear with the emergency brake on and chocks there is a similar flicker. Readings from the multi meter:
Battery - 13.86-13.89; Courtesy or reading light connector - 13.29-13.37; RPMs - slightly above 500 (same as in park)
Next, if you do, carefully have a second set of hands go around "nudging" things to see if they can find a "connection issue".
Tried some nudging of various connections and grounds with no effect that I can tell.
Next, if you don't have the issue in park, next try in gear with the brake on (firmly). Do you get "flicker". Again, have the second set of hands nudge things and observe. As roadie asked what is your idle engine speed in park and in gear???
Well, hopefully the above helps take me to the next step, and I appreciate all the advice and input!
while I think that helps quite a bit. First, the "in park, in driveway", basically helps eliminate any "going down the road" testing and suggestions that bumps and such from the road are an issue. Second, it is then more easy to do some more.... BUT you likely don't have to... I think your idle is way too low. At least based on my limited experience. Mine sets at around 625-650... are you sure that you are reading that correctly. IF so, I suspect you are limiting the output of your alternator... at least in idle / park.... but of course, that doesn't explain things IF this happens going down the road at "full clip". However, it may be that because of the low idle, that perhaps your battery isn't fully charging resulting in a "constantly strained" system... just my thoughts right now.
Also... note your battery voltage readings with a meter versus the gage... a "slight difference"... but potentially interesting.... unless your meter is off quite a bit (ie. uncalibrated), those readings appear to be a little low. So there is some "funnies"... a low rpm reading and more interesting a low battery reading. My "new guess" is that you have an alternator issue either in terms of a "lost rectifier" resulting in a "less than true DC voltage" or possibly a "brush issue" such that is not always in contact.
Driving around a bit today and based on comments from budwich, decided maybe I should put the multi meter back on the battery and repeat the tests from the other night just to check and here's what we have today:
With the Envoy in park, AC on & lights on, yes there is a flicker. Readings from the multi meter:
Battery - 14.00-14.05; RPMs - slightly above 500
With the Envoy in the driveway in gear with the emergency brake on and chocks there is a similar flicker. Readings from the multi meter:
Battery - 14.01-14.06; RPMs - slightly above 500 (same as in park)
So those battery reading are a tick higher than the other night's tests using the same multi meter. Would there be some logical explanation for the difference or is that normal? It's about .15-.18 volts higher tonight.
I am a little bit concerned about the RPMs being low. I've read a bunch of threads about owners getting their PCM flashed/updated but I can't find exactly which ones addressed this issue. Does that matter or will the dealer automatically catch up all the updates missing? And a few weeks ago, just to try and troubleshoot some issues, I broke down and went to the dealer to check and they said I didn't need a PCM update but that was for some random hesitation accelerating from a stop, so maybe they just didn't think the random hesitation had anything to do with the PCM?
With the Envoy in park, AC on & lights on, yes there is a flicker. Readings from the multi meter:
Battery - 14.00-14.05; RPMs - slightly above 500
With the Envoy in the driveway in gear with the emergency brake on and chocks there is a similar flicker. Readings from the multi meter:
Battery - 14.01-14.06; RPMs - slightly above 500 (same as in park)
So those battery reading are a tick higher than the other night's tests using the same multi meter. Would there be some logical explanation for the difference or is that normal? It's about .15-.18 volts higher tonight.
I am a little bit concerned about the RPMs being low. I've read a bunch of threads about owners getting their PCM flashed/updated but I can't find exactly which ones addressed this issue. Does that matter or will the dealer automatically catch up all the updates missing? And a few weeks ago, just to try and troubleshoot some issues, I broke down and went to the dealer to check and they said I didn't need a PCM update but that was for some random hesitation accelerating from a stop, so maybe they just didn't think the random hesitation had anything to do with the PCM?
0.3 or even 0.4V is within normal tolerances for temperature changes and state of charge of the battery.
When you see flicker, what sort of frequency is it? 1 Hz, or 5 Hz? Or slower?
If the battery is stable, and a good one sort of HAS to be due to the physics, put your meter on something that's flickering. Measure it where you see the problem.
If you don't see the meter moving on DC volts, change to AC and report those readings.
How do you know the RPMs are low? By reading with a scan tool or looking at the inaccurate tach? Don't obsess over that. The normal PCM table forces the idle to be 612 RPM typically (or 625, I forget). The PCM is a lot more accurate than the tach stepper motor display.
When you see flicker, what sort of frequency is it? 1 Hz, or 5 Hz? Or slower?
If the battery is stable, and a good one sort of HAS to be due to the physics, put your meter on something that's flickering. Measure it where you see the problem.
If you don't see the meter moving on DC volts, change to AC and report those readings.
How do you know the RPMs are low? By reading with a scan tool or looking at the inaccurate tach? Don't obsess over that. The normal PCM table forces the idle to be 612 RPM typically (or 625, I forget). The PCM is a lot more accurate than the tach stepper motor display.
Only from the dash tach - haven't invested in a scan tool yet but that's probably coming real soon! Maybe I've convinced myself it's to slow but it certainly "feels" smoother and more "normal" when I raise the RPMs pressing the gas pedal slightly and the dash tach shows the RPMs around 650. That's not very scientific I know.the roadie said:
any ways, unless the voltage swings have some "time" to them, it is unlikely that a digital multimeter will see anything either.
When was the last time you cleaned your throttle body? Further, you can get a ~$30 odb interface for your computer (or otherwise) with free software that will give you a lot more info which might help you out.
I guess the one question for right now is "has your rpms always read 500 at idle / park"????
When was the last time you cleaned your throttle body? Further, you can get a ~$30 odb interface for your computer (or otherwise) with free software that will give you a lot more info which might help you out.
I guess the one question for right now is "has your rpms always read 500 at idle / park"????
I wish I could remember - that's awful to admit I know but I really don't remember noticing what the RPMs were reading over the years. I've really not had many problems until about 3 or 4 months ago and it seems I've had to replace a bunch of things. It all kinda started with the engine "feeling" like it was running a bit rich and stalled out a few times, then the coils started going. That's when I started on the Trailvoy site and now this site.budwich said:
You just need better tools than the goofy instrument cluster. The truth is out there.jimmackey11 said:
the roadie said:You just need better tools than the goofy instrument cluster. The truth is out there.
Fox Mulder would be proud! Now, for recommendations on best options for a scan tool? Man, love this site! I'm learning a lot and have a long way to go!
If you have an Android phone, search this site for discussions about the "Torque" app. No need to buy more than a Bluetooth OBDII dongle and the cheap app to do everything a $100-150 scan tool can do.
Darkrider_LS
Member
- Jan 25, 2013
- 9,332
the roadie said:
Torque app is nice! I have been using the free version for awhile now and will probably be moving to the paid version soon.
meerschm
Member
- Aug 26, 2012
- 1,079
ScanTool.net LLC - OBDLink SX Scan Tool/OBD Interface - ScanTool.net
if you have a laptop PC.
is another option.
android or apple smart phones make Roadie's suggestion a more tempting alternative.
if you have a laptop PC.
is another option.
android or apple smart phones make Roadie's suggestion a more tempting alternative.
Actually that "history" is probably just as important as your current thread posts. First, did you put your system thru a "relearn cycle" when you installed the new throttle body??? IF not, that could explain issues with idle rpm and maybe a lot more. The "coil issue" is perhaps some what interesting as it maybe related to an "imbedded" electrical issue that you are seeing with the flicker.... maybe...jimmackey11 said:
I am still thinking that your idle is too low putting issues on your electrical system in terms of long term drains and also possible a loss of a rectifier on your alternator resulting in "less than DC" which might be a cause for a few things.
Anyways, personally, I use a cheap odb interface to a mini-pc, works fine for most things but as other have suggested there are many options but I think they will help you both now and in the future.
the roadie said:You just need better tools than the goofy instrument cluster. The truth is out there.
Roadie - a quick question - do you reprogram (or whatever the correct term is) your PCM using the ODB scanning tool/app or do you just use it for getting info? There seems to be a few programs out there that say you can "tune" your PCM but I'm also finding a lot of info out there that says you can only do that if you get a separate tuning app and hardware. So, what's the real truth on all this?
I've got a bluetooth ODB2 interface on order.
budwich said:
I agree with budwich on this. I took an alternator with a known-bad diode problem to autozone for their bench test and it passed. I also tested that alternator on a vat45 with it in the vehicle, and it passed both the output test and the diode test. The only tool that caught it was a lab scope that could graph a diode pattern (OTC vision). The reason I say this is because it proved to me that the common tools for testing alternators can't pick up "small" diode problems - they really have to fail to set a red flag. The symptoms that the vehicle (02 Trailblazer) was having was flickering lights - headlights, interior lights, etc, worse at idle in park. The hotter the alt got, the more noticeable the flicker was. A new alt solved the issue. And just because the alt is new doesn't mean anything. I've installed plenty of new alternators that had issues right out the box.
If this is referring to the "new" procedure that has been floating around recently, there is no evidence to support that it is necessary (or actually does anything).
MAY03LT said:
I have seen more than one person say the same thing - it makes me wonder if I should just replace the alternator. Also, does anyone have some advice on the alternator brand? Usually the OEM AC Delco is the standard answer but those are really hard to find so hunt down the AC Delco one or is there a "better" brand? I have also seen where people have installed a 200 amp alternator and not the 150 amp so is there any benefit to that? I would imagine you can go too high on the amps and start frying stuff as the wires won;t be the right gauge?
MAY03LT said:
From reading a couple of places not sure if it was only here, but I guess I would do anything to check out my idle speed. I know from my limit recent experience with my TB that after "messing" with the tb, I did some sort of "start up sequence" to allow the thing to find "base conditions" which were a bit different before the "messing".
budwich said:
I've done the battery disconnect while changing the TB. I also did the "relearn" of sorts where you disconnect the TB, then disconnect the battery for at least 30 minutes, then reconnect the TB, then the battery to force it to do some sort of reset. If there is another option I'd be glad to try it!
Interesting observations this morning - had to go to work early this morning so while it was still quite dark, jumped in the Envoy and started it up. I had the door open still and the courtesy/reading lights started immediate to flicker at a pretty good rate. It was in park, lights on, no AC. The flicker lasted a good 15 seconds or so while the RPMs were still quite high (as normal at startup), but then as the RPMs came down to roughly 500 on the tach the flickering appeared to stop or be unnoticeable. I believe the alternator does not kick on right away at cold startup and takes 15-20 seconds to do so. Does this mean the alternator is ok and the flickering is something else?
but only you can tell us if your alternator was working... what did your voltage gage indicate during the time period? Personally, I think you have an alternator issue.
Vicompc
Member
- Dec 5, 2011
- 109
budwich said:
I agree, this is the same issue a I had. My altenator passed the Bench tests but it turned out it had a bad Diode that was causing the fluctuations. I tried a Napa brand alternator and an Autozone one and had the same issue, I ended up putting in a AC Delco from GM and have had no more issues sense.
