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THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHVoltmeter reading
Reported or suspected cause
likely caused by the "y" cable
Reported cause
No successful repair reported for this finding.
1
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Reported cause · Original poster
It looked like the problem was likely caused by the "y" cable so i bought one.
Leading evidence: 'likely caused by the "y" cable' (1 discussions report identifying this cause; no attributable repair resolution). Across 1 matching discussions, the most frequently mentioned possible cause is 'likely caused by the "y" cable' (1 discussions; 1 report identifying it and 0 suggest it). The most frequently discussed action is 'Check /' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Performed · outcome unconfirmed · Original poster
Further testing pointed to the alternator so they installed a Bosch re-build.
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Performed · outcome unconfirmed
I replaced the engine ground strap about 6 months ago; that eliminated an entire tribe of gremlins
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Performed · outcome unconfirmed · Original poster
Got ready to start work and ran into a time crunch with an upcoming trip.
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Suspected cause · Original poster
I suspect it was the alternator that was the culprit all along but the "y" cable certainly was due for replacement.
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Suggestion · Original poster
Was able to get a pretty stable reading around 13.65v and when i would lift the ground the readings went to random, replacing the ground the meter went back to 13.65.
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Suggestion · Original poster
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.
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Suggestion · Original poster
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?
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22 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
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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?
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.
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.
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.
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.
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.
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.
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.
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?
It's important to get to the back of the alternator because if the starter y-cable is bad, the voltage will be lower at the engine bay positive lug.
Please see the j hook tool I made to probe the back of the alternator
here
.
I did make that hook to reach the back of the alternator. The instructions describe testing between the alternator back to the battery terminals (B+ and B-) so it sounds like I also need wires to run to the battery, or can I take those readings using the engine bay positive lug and the chassis as the ground?
I did take just readings at both the battery (B+ to B-) and at the engine bay positive lug to chassis (lug at air cleaner mount) with the engine off and got the same reading (12.64v at both locations). With the engine on I got 12.53v at the battery and 12.64 at the engine bay positive terminal/chassis..
If you perform tests 1-5, you should be able to id the culprit. It's important to follow the steps as written in the instruction.
If you suspect the alternator, one quick test (test #5) is measure the voltage between the back of the alternator (using the hook) and the alternator case. When the engine is running (at idle) and with some load like low beam and a/c ON, the alternator should output at least 13.5v
I was able to get a reading on test #5. Was able to get a pretty stable reading around 13.65v and when i would lift the ground the readings went to random, replacing the ground the meter went back to 13.65. Repeated this several times for confirmation. So it doesn't look like the alternator is a fault. More like one of the cables so I'll test for that, esp #3 for the Y-cable. I guess that's good new about the alternator. I suspect this is the original Y-cable.
I thought an update on this problem might be useful to someone else.
It looked like the problem was likely caused by the "y" cable so i bought one. Got it ready to install (removed the "box" on the end so i could work the cable into place without removing the A/C). Got ready to start work and ran into a time crunch with an upcoming trip. So I decided just to wait until winter when i would be installing the M030 suspension to tackle this at the same time. So the gods of procrastination got me. I had to drive down to Phoenix (about 2 hrs away ) to visit Evoms for a mod to my air intake system. When they went to pull the car into the shop the battery was flat dead. Further testing pointed to the alternator so they installed a Bosch re-build. Had them install the new "y" cable at the same time. The old cable was definitely corroded but not completely shot. Between the two new parts, the car now starts easily and the voltmeter on the dash now reads around 14v when it is started up. I suspect it was the alternator that was the culprit all along but the "y" cable certainly was due for replacement.
Big take-away, don't procrastinate........
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