2005 Tahoe Battery Light stays on and the speedo needle jumps while setting or driving

[dracer398]

Hi All!
I have a 2005 Tahoe that was setting for a while. It was running fine with no issues untill I parked it because of a blown rear brake line. The battery went dead co I charged it and got it running. I noticed the Speedo needle was jumping just setting there idling and also driving. I also noticed the battery Light was on. The alternator seemed to be working because it was showing around 14 volts. I shut it off and disconnected the battery. I grounded the positive cable to clear the codes. I reconnected everything and started it. I got the same results. So I connected my scanner and cleared the codes. Didn't help...
Has anyone ever had this issue before?

Thanks in advance,
Brian

[aleekat]

What were the codes? Was the 14v measured with a voltmeter or the gauge?

[Blue Bowtie]

2005 was in the range of years (2003-06) where GM had aging problems with some of the stepper motors in the instrument clusters.

While that MIGHT explain the speedo jumping around with no signal, it would not explain the BATT warning light being on. That's a charging issue or problem with the alternator wiring. Instead of the in-dash voltmeter, use a handheld diagnostic meter as @aleekat suggested in his question.

If you get the engine running, check the alternator output stud voltage, but don't just check D.C. voltage. Set the meter on an AC voltage scale and read the level of AC present. It shouldn't be much over 0.07 V, and anything too much higher can affect all kinds of systems, the instrument cluster included.

If you are under the hood spending some "quality time" with your conveyance, it would also be good to inspect the grounds, including the engine ground(s) at the intake/rear of the head to the firewall.

[dracer398]

Aleekat, it was measured with the dash gauge, my scanner was reading 13.6. Blue Bowtie I did measure at the alternator stud, AC voltage was .01 and voltage measured at the stud was 13.68v dc. I did a load test on the battery and it was in the "Weak" zone. So I'm going to try another battery. I checked the ground on the left cylinder head to body and the connections were clean.

[aleekat]

Your battery may be weak but your alternator should be putting out over 14v. Turn on everything and see what your alternator is putting out.

[dracer398]

Well, I changed the battery somehow this helped clear two lights after driving the vehicle for a while. It cleared my brake light (Code C0131) and cleared my traction control light. I ordered a reman alternator. I hope this cures the battery light and maybe the jumping speedo needle. The needle sometimes quits jumping but no speedo indication.

[aleekat]

Check the charging voltage after install. Remans have been know to be bad out of the box.

[dracer398]

Update: I changed the stepper motor on the speedometer and it still jumping. I got my new alternator but I haven't had time to install it. I'm also going to add extra body to engine and engine to chassis grounds. Hopefully this will work. I also found that some critter took residency in my under hood fuse block. I vacuumed all his left over garbage out but I think I need to clean the fuses and connectors. Is there a good safe way to clean this?

[maxwedge]

CRC electrical parts cleaner.

[Blue Bowtie]

If the temporary residents also used the UEC as an outhouse, it may require deeper cleaning and some repairs to corroded connections. One opened up, flipped, and the lower cover is removed, the potential for connection issues becomes apparent. You might be shopping for a 15786043 somewhere.

[dracer398]

Well, I dug deeper into the under hood fuse block. There was another nest under the fuse block. I remove the nest and found that the rodents chewed up my wiring. I had to solder in two wires that they completely chewed through. Then all the other damaged insulation I coated liberally with liquid tape. Now the speedometer works as it should and my battery light is off. Mice can do some pretty bad damage. I hope the little guy that was under my fuse block needs dentures after this!!! LOL

[Blue Bowtie]

Good work. It's fortunate that you have an obvious reason for the wiring damage. I've had some of those UECs deteriorate just from atmosphere and weather, and wire harnesses which seem to fail for no apparent reason, inside a wrapped harness, with no evidence of physical damage.

Hopefully that resolves the vehicle issue. Now on to the rodent population.