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Ever since I got this 1997 c5 I've been trying to sort a few things.
I consistently have a lower than normal voltage reading on the dash gauge.
Now. Here's my situation. Car starts / Runs / Drives fine. I do not have any cranking hesitation or sign of a weak battery. I do not nor have I seen a charging circuit error. Car made it home on a 90 mile trip without issue.
BUT the dash seems to think the voltage is way lower than my real time measurements.
Here's the situation and my observations.
Key on, not running:
Voltage at underhood fuse panel b+ terminal:
Voltage displayed on DIC:
I actually took video of both with the car running but dont' know how to put the video up here, but the basic idea is this:
All engine running measurements were taken at idle.
DVM (connected to underhood fuse center b+ terminal) shows 13.6-14.1 volts with the car running.
DIC shows 12.0 - 12.7 volts with the car running, and jumps constantly and erratically between those numbers.
Now I decided to test voltage at the only readily accessible spot I could think of - the power port in the center console:
Engine off:
Engine running:
This is what I have done so far:
After searching on this site I found a thread about the ignition switches causing problems. I replaced the ignition switch with a BRAND NEW one from a GM dealer. I actually replaced the ignition switch, and found the wires bunged up with t-taps etc from a previous remote start installation. BUT that had no appreciable affect on the dash's display.
I'm scratching my head and considered swapping out the alternator, but the mechanic / engineer in me says that it doesn't make sense. If batt voltage was really that low, I'd have a hell of a time cranking the car. I don't. If the alt wasn't charging properly, I'd kill the battery, or have other issues. I don't.
Add in all my other measurements, and my logic dictates that the charging system is just fine, but that the volt gauge in the DIC is just bad.
My car has had the cluster out, to add the aluminum gauge rings, and led backlighting (by the previous owner). I'm wondering if either of those two things (or setting a needle in the wrong place etc) could mess up the gauge?
Has anyone ever seen an inaccurate volt gauge in one of these cars?
I resoldered my climate control panel and got the display back. I've replaced stepper motors in GM Truck / SUV's several times, and resoldered / replaced resistors in third gen f body clusters bc of the tach going crazy, so it wouldn't surprise me if something in the electronics was causing the gauge to indicate low.
Dash gauges are downstream of the ignition switch as you may know.
I recently replaced the ignition switch in a friends 2004 (60K miles)because he consistently was seeing voltages of under 13 volts on the dash gauges while driving yet after significant manual recording of voltages at the battery and at the alternator those were consistently between 13.7 and 14.2. So clearly the battery was being properly charged but the reporting mechanism was not reporting accurate information. Gauges being downstream of the ignition switch was our basis for changing the ignition switch. Voltages at the fuses after the ignition switch were about 0.3 volts more than what the dash gauges were reporting so we knew the gauges were not terrifically accurate..
After the replacement of the ignition switch the dash gauge readings now show about 0.5 volts less than the voltages at the battery and alternator. Voltages at the fuses before the electrical devices that are supplied by the ignition switch show about 0.1 volts less than the battery and alternator. So we have concluded that the instrumentation that displays the voltages is either inaccurate or has resistance after the fuse. Either way it was not worth any further effort to try and isolate the problem further in our estimation. More junk electrical from GM. Should we expect better on a car that originally sold for over 60K.
The major difference on this 2004 is that the voltage display does NOT have the jumping values that you experience. HTH.....
PS, when we opened the original ignition switch the contact surfaces had significant scorching and pitting. In fact almost identical to those shown in the Bill Curlee thread about servicing the ignition switch.
I JUST replaced the ignition switch, that was my initial thought as well, based on Bill Curlee's thread. Made no difference whatsoever in as far as the dash except it seemed to read a bit higher when the car was running, albeit still low (I have never seen 13v on the dic). It seems to be 1 - 1.5v low. I will open my old one up and look at what the contacts look like this evening. I need to check voltage @ said fuses powered by the ignition switch.
With the car off I'm seeing 10.8v on the DIC and 12.3v on the Battery.
Like I said other than the DIC gauge having an crazy display. Everything else seems fine. My dash with the car running will go 12.7v 12.5v 12.3v 12.5v 12.7v and repeat in as long as it will take you to read that. Seems like I was getting about .2-.3v lower readings before the ignition switch swap.
If we extrapolate that -1.5v as a semi consistent error, then the Alternator is putting out 14.2v, 13.8v, 14v, and 14.2v respectively during that display cycle. Which WOULD seem perfectly normal.
I'm wondering if some sort of resistor (or solder joint) is failing in both your friends 04 and my 97, with mine having more of a readout discrepancy because of another 7 years of age affecting it. It's certainly happened in other GM products. And even in my c5's HVAC control panel.
Hey, I watched a trailblazer catch the rear tail light harness on fire, and apparently their window switches also catch fire. I don't understand GM's propensity to run high electrical currents through mechanical connections. Haven't they heard of relays?
All of these buttons, controls etc should be just triggers to relays designed to handle high current loads.
Thanks for the insight. You seem to be confirming my theory that the alternator is fine, but the dash just doesn't want to play along.
GM does use relays but they consistently undersize those as well. Wait until you start having problems with the door locks not working.
Was the 12.3 volts battery voltage you reported what you are reading with a digital multi meter with the engine off???
If so that is LOW. It should be above 12.5. In fact the No Load voltage of the battery on a good fully charged battery should be between 12.7 and 12.9 volts or more. No Load voltage is the battery voltage across the battery posts with the neg battery cable disconnected. Many of the electronics in the car will not function correctly with No Load voltage at 12.5 or less, although the car will start with 12.2 volts or less. Electronics just are not happy. Things like the BCM for example.
You might want to try charging your battery fully and see what you get.
Yes sir. 12.31v engine off BUT the battery connected to the car still. In fact the interior lights may have been on. This car has an off brand "hi tech" battery in it. (That's the way I bought it) and when I bought it the keyfobs had to be reprogrammed and the time was off on the radio - hence at some point the battery had gone dead. I have a battery tester at my shop. I should do a battery test and an alternator test eh?
Alternator seems to be OK based on the voltages with the engine running. I would test and charge the battery to insure it is at FULL charge if you think it may have been dead at one point.
I have a 10 amp fast charger, and one of those 2.5 amp trickle charger / maintainers. I'll throw it on the maintainer and see what it has to say - it usually gives me a "battery percentage" reading, I'll leave it on overnight until it goes into maintenance mode.
Actually the 12.31 v reading may be with the interior lights on etc. After doing all my tests, (and the car running for 10 or so min), I shut it off and then tested the power port on the center console and it showed 12.49v with the car off.
I haven't really driven this car much because of this whole voltage issue. It's kind of shaken my confidence in taking the car on longer trips because of the fact that I really have no desire to get stuck somewhere. Would you recommend an optima for the c5? I have one in my impala SS.
09-16-2014, 01:05 PM
Is my alternator bad or is my dash just crazy??
