az968gpw

The voltmeter on my '04's dash has been reading just between 12v to 13v while driving at all speeds, maybe closer to 13v at higher revs. This seems too low to me. What is normal reading? The battery is new, so thinking alternator or voltage regulator not working properly?

sasilverbullet

I wouldn't trust the meter on the dash, take it to autozone and have them check/test the battery.

Ahsai

Normal reading is 13.5v-14.5v at idle fully warmed up. Even 13v is too low and not enough to charge the battery properly.

Usually it's closer to 14v right after cold start. You may want to use a known good digital voltmeter to confirm the reading first.

az968gpw

Wasn't hitting close to 13.5v per the voltmeter. Sounds like it might not be charging properly. I'm concerned I could be stranded somewhere if it's not charging properly. So I guess it's off to the shop for testing.

I put the car on a battery tinder shortly before leaving for a few weeks, The tinder ran all night so i unplugged the tender before leading worried that i might damage some component.

Ahsai

A battery tender is designed to be connected to the battery for a long time (months) without issues. Note a fully charged battery will make the alternator output a lower voltage in general. However, that voltage should still be 13.5v or higher.

Mbren1979

A few things to add. When the car is running the gauge is reading charging voltage and not battery voltage. Gauges are sadly not much different then a dummy light, the info it provides is limited. To give an example, temp gauges have a happy spot so to speak. That temp is what is normal for the car to run at. Lets say that temp is 180 degrees on the gauge. The actual sending unit and pcm could be reading in the range of 160 to 210 but the gauge is engineered to show 180 while its at those temps. GM actually has a bulletin explaining this on newer models. Some gauges actually reflect real info. All depends on what each manufacturer sets up. When it comes to voltage - it can vary depending on loads. Are the headlights on? Fans on? A/C on? Blower motor on high? All these loads will varys the voltage demands. Simple answer is while the car is running you should expect to see more than battery voltage (12.6 V). You could see 12.8 up to 14.8 depending on demands and what the voltage regulator is asking for. If your concerned have a qualified mechanic check it out.

az968gpw

I need to do that as sometimes after driving it is slow to crank. Like not getting enough voltage to the starter.

Mbren1979

May not be a bad idea. The 996's are common for engine ground strap issues as well as corrosion build up in the positive cables between the starter and alternator. This issues will cause the same complaint and can be tough to diag.

az968gpw

Thanks, I'll check the power cables and see if that's an issue. The engine was out of the car about 16k miles ago (presume the cables at the starter and alternator were cleared of any corrosion then) and the battery connections are good (new battery) so might be something in between. I'll pull wiring diagrams.

dan_189

Most likely either the alternator to starter cable or the starter itself - or both

Ahsai

See my write-up here for thorough troubleshooting.

az968gpw

That's a great reference, thanks! I'll start there and see what it tells me.

porschedog

I replaced the engine ground strap about 6 months ago; that eliminated an entire tribe of gremlins

Ahsai

A short cut to diagnose a bad ground strap: when you are experiencing low voltage, use a jumper cable to bridge between the brass ground bolt on the intake air cleaner and the engine brace/any exhaust components (under the car). If the voltage jumps significantly, you have a bad ground strap.

az968gpw

Before starting the diagnosis process I thought it best to get the battery up to full charge so I left in on the battery tender for several days. It's was now showing charged, per the tender. The digital voltmeter I'm using to test with read 13.28v on the battery with the engine off after the battery tender showed fully charged and before driving the car. After driving the car in town for about 30 min the battery read 12.4v with the engine on and the a/c and lights on, and 12.59 after turning off the engine. That seems too low per guidance from earlier comments above.So now to start tracking down the problem. In the instructions i downloaded from the link Ahsai posted above it describes reading the voltage from the B+ and B- battery posts. Do you actually run wires from the engine compartment area to the battery posts for this or use the + lug just above the a/c compressor and the chassis ground?