My proble. Is my 02 envoy voltmeter was under charging. So I checked battery and found positive cable hot ot touch, burned finger. Further inspection found corrosion at +cable wires. Stripped insulation back cleaned all corrosion and reassembled. Started truck checked cables no more heat. But then noticed volts fluctuating between 14.7-15.9. Tested with dvm same readings. Turned on all accessories volts kept going up. Put it in gear volts came down some. Very erratic readings. Prior to all this meter read at 14 volts. Lost as to what it could be altenator or pcm. I have continuity at red and grey wires at alt connector. Any help would be appreciated. Also no codes.
Erratic volt readings
- Thread starter dwalts55
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Mooseman
Moderator
Thanks for reply.. Battery tested at auto zone and advance auto. Tested good. Batt. Has held 12.7 volts. Draw test with starter dropped to 11.3.
Mooseman
Moderator
Yes the lights flicker at times. Advance auto tested alt on car. 15.7 output. I turned on all accessories just a little drop then back up. I cleaned grounds, tested grounds, inspected mounting bolts loosened and retorqued the. (That lower on sucks.lol). Did a ground ckt. Voltage drop test alt housing to negative post 0.4. Also swapped battery from my other car. (Same type batt). No difference. I'm baffled. I'm thinking when that cable got hot the regulator may have overworked and got damaged but not completely blown. I should add vehicle has 290k miles.
what are you disconnecting at the alternator... the "multi wire" / control plug or the "output" plug / wire? It would appear from your description, that the alternator is putting out a "normal" voltage with "no load" (assuming that you disconnected the output wire and measured there). Then, if it is loaded, there is a problem and the voltage goes high. That would point at the regulator or the alternator itself. The problem is you need to see the actual output characteristic (ie waveform). This would confirm what is up. My guess that the advance auto test is telling you what you know. You didn't indicate what they actually said.... other than the voltage reading... did they say "it is your alternator"?
another test that you can run.... disconnect the alternator plug (control signal wires). Key on engine off, measure the voltage at the generator turn on signal / wire (to ground)... what is the reading?
Of course, you started with "it is not charging" and it is odd then the voltage is so high and still the complaint. Of course, a clamp on meter would tell how much current is being output readily on the red output wire... that would probably be to nice to happen. Lucky I got one of those (cheap but works)....
One last point, do you have a battery indicator on in the instrument panel?
Of course, you started with "it is not charging" and it is odd then the voltage is so high and still the complaint. Of course, a clamp on meter would tell how much current is being output readily on the red output wire... that would probably be to nice to happen. Lucky I got one of those (cheap but works)....
One last point, do you have a battery indicator on in the instrument panel?
I disconnected the 2 wire control plug and measured at battery. I did not load it up also I idid not test the turn on signal at connector. I will check that this morning. The advance auto guy said the alt was overcharging and bad. But he wasn't confident in it. Also there is no battery light on in dash and no pcm codes. I can't check bcm codes. Just never had gauge bounce around this much b4. A little history. About 3 years ago the gauge started discharging. The connections on battery were corroded so I cleaned them up and its been fine till now. So I cleaned again this time, but cut back some insulation where some corrosion formed and now these arratic readings. I'll post what my next tests revealed. Again thank you.another test that you can run.... disconnect the alternator plug (control signal wires). Key on engine off, measure the voltage at the generator turn on signal / wire (to ground)... what is the reading?
Of course, you started with "it is not charging" and it is odd then the voltage is so high and still the complaint. Of course, a clamp on meter would tell how much current is being output readily on the red output wire... that would probably be to nice to happen. Lucky I got one of those (cheap but works)....
One last point, do you have a battery indicator on in the instrument panel?
Ok. Disconnected the alt plug 2 wire connector. Measured voltage at gen. turn on wire at 5v. I assume this is 5 volt reference.
Started engine with control plug disconnected. Tested volts at batter terminals it was 11.8. Must have done something different yesterday. Turned off eng. Plugged in alt. restarted eng . At idle volts 14.3 to 14.9. Once in awhile it would go to 15.2. Turned on everything in truck. Volts read from 13.5 up to 14.9 and maybe hit 15.2. At 1500 rpm in gear everything on 14.0 to 15.1. So its not bad today. I hate electrical.lol. But I am using a 20 dollar meter, so. From what I found 15.5v is not out of range for this vehicle?
not sure what you mean about "cutting back the insulation"... the factory connectors on the cables are "crimp style" wire eyes / bolt ons... so I don't understand what you did.
You measurement of the gen on appears to be somewhat high (spec indicates 4.7)... but maybe your meter or other things in the measuring points.
Again... you posted that your system is "under charging"... why are you stating this? A voltage meter can't really determine "charging" unto itself... only an ammeter can determine "charging".
It appears that your battery is charging both as tested by advance auto and via your meter observations. The only thing left to check is the "duty cycle" sent on the other control wire. You need a scope to look at that or a high end obd interface to get the duty cycle data. Further, the duty cycle appears to b a status line and thus the only control of the alternator itself is the on/off associated with the "gen on" line which can be commanded via an tech2 or equivalent for full on / off.
You indicate that you have 200k plus... on the original alternator... if so, the brushes / commutator are probably well worn which probably doesn't help.
You measurement of the gen on appears to be somewhat high (spec indicates 4.7)... but maybe your meter or other things in the measuring points.
Again... you posted that your system is "under charging"... why are you stating this? A voltage meter can't really determine "charging" unto itself... only an ammeter can determine "charging".
It appears that your battery is charging both as tested by advance auto and via your meter observations. The only thing left to check is the "duty cycle" sent on the other control wire. You need a scope to look at that or a high end obd interface to get the duty cycle data. Further, the duty cycle appears to b a status line and thus the only control of the alternator itself is the on/off associated with the "gen on" line which can be commanded via an tech2 or equivalent for full on / off.
You indicate that you have 200k plus... on the original alternator... if so, the brushes / commutator are probably well worn which probably doesn't help.
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My apologies, I should have mentioned that when I had this problem years ago I cut off the factory cable mounts and installed clamp on ones. Thats why I stripped insulation back. The dash gauge showed volts dropping. Got home found positive cable very hot and some corrosion at wire. Disconnected peeled back insulation cleaned more corrosion. Reattached to batt. started veh, dash meter read charging now, but went up to high volts. Then I put dvm on it. Thats when I got high readings.
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Let me add yesterday I took a break from the truck to do some yard work. When I got back on it I saw gauge in normal range so decided to take for a drive. Gauge stayed around 14 with little movement. (Normal area). It got dark so lights came on and I had a/c and blower on. All ok till came to stoplight. At light noticed gauge climb between. 14 and 19 and lights flickering. Then whole go down and up till I accelerated. Then it went to normal range. Think Monday I'll take it to a shop with good equipment have them check waves. Just don't want to go through replacing alt and it be the pcm. Pic not accurate. Did go up 2 more hash marks. Took phone to long to snap pic.
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Mooseman
Moderator
Alternators will go into high output like that when there is a poor connection at the battery (or no battery). I wouldn't have a lot of trust in that setup. The fact it gets hot shows high resistance created by a poor connection. I'd get a proper connector.