I'm wondering if either is on the way out on my wife's MK4 Golf (X-plate).
I don't really want to go to a garage tomorrow (Kwik Fit being the only one open locally) and say hi can you test this for no charge >IF< vagcom can do the job for free. I have a full version of vagcom, I'm just not great at using it fully.
The car had been ok for long enough. The battery is maybe 12-18 months old. A tire was flat yesterday so I had the car running while using the compressor to blow it up.
Wife drove about 20 miles out. Didn't start great but started. When she came to come back home the car wouldn't start.
I jumped it and as she approached home it started to judder a bit I think she said. Then she parked it up on the drive. Came to start it again and it wouldn't start.
All dash lights come on as they should. Fans blow as they should. The radio will work. Remote locking still works.
I've got a battery charger on there at the moment but having a chat with someone about it they say it'll likely be the alternator.
Just wondered if there was some reading or test in vagcom that would help identify if either battery or alternator is good.
From what I've seen of the VAGCOM and the US-market Mk.4 Golf, I don't think the VAGCOM is gonna be the tool of choice in this situation.
Most VW's I've seen of this vintage have internally regulated alternators, meaning that the PCM has no input on charging rate. So, there likely won't be a bidirectional command for the alternator, or any kind of feedback data on field strength.
You'll definitely have some kind of battery voltage PID, but that won't tell you anything a good ol' DMM can't. :silly: You could absolutely use the VAGCOM to verify that the alternator isn't charging the battery, but not much more.
A DMM and a test light will be much better, IMO. With those, you can voltage drop the battery cables, block ground, and verify the regulator has what it needs to work.
As above --- VAG Com will give you charging voltage but it isn't a reliable indicator. A cheap digital multi-meter is more suited
I take you have already checked the battery connections are clean and tight.
After you charge the battery (4 hours absolute minimum 8 hours is better)) when it is in the car turn the side lights on for 3 or 4 minutes then switch them off. off and check the voltage across the battery if it is still below 12.4 volts it is possible you have some kind of battery fault but first try charging the battery for a few more hours if no improvement get the battery tested. A good fully charged battery in the current UK weather should produce about 12.6 volts across the terminnals.
Once you have the battery connected in the car with engine running at idle lights, and other loads such as the heater fan off typically expect the voltage across the battery to be about 13.7 to 14.7v , raise the rpm to around 2,500 the voltage may should stay below 14.9 volts. Turn the headlights on and again with the headlights on check the voltage at idle and 2,500 rpm. Then hold the engine speed to 2,500 RPM and turn the lights of the voltage should not at any pointin these tests drop below 13.4v or jump above 14.9v.
You can do an additional test with all major electrical loads on, lights, heater blower, radio on, with all loads on at idle battery the battery voltage should stay above about 13.1 volts.
These are the most basic tests you can do on an alternator.
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