Hi. I've got my local friendly garage load testing the battery/alternator in the morning, but thought I'd ask here for additional support for this issue.
For a couple of days now, I've had the battery light flickering at me but the light never flickers consistently.
At low rev's (below 2500-3000RPM) the light is almost always on. At higher rev's (above 2500-3000RPM) the light is almost always off. But that's only if the engine is under load, if I'm booting it (I have booted it and the light has stayed on above 3000RPM a couple of times). If I feather the throttle above 3000RPM the light will probably still be on. If I rev to say 5000RPM, the light is off under load, but if I let off the throttle the light comes on from 5000RPM all the way down to idle. Odd. A sharp right hand corner at 1500RPM might turn the light off too, but not always.
Last night on the way home I got approximately 6 miles down the road and the voltage was dropping, I know this as things like the ABS and DSC light lit up, airbag light then the voltage dropped that much that the xenon's stopped working so I pulled over into a closed petrol station. I left the engine running and removed the airbox. By this point the ABS, DSC and airbag lights had gone dim due to the low voltage, the engine remained running but was struggling to run. I played with the big red wire that goes to the jump point on the drivers side strut and twatted the alternator out of frustration, and a few seconds later the car sprung back to life. All lights on the dash went out including the battery light and I could turn the headlights back on. I drove the car home a further 14 miles and the battery light didn't even come on once. I'm not sure if hitting the alternator was a coincidence or not.
This morning I started the car and the battery light was on again. I got the car to work (20 miles). I left work and used the OBC to read the voltage which was approximately 12.4v with engine running. After about 2 miles, the battery light went out and the voltage reading went up to 14.1v. It stayed at that for about 10 miles. I turned the heater on and everything was fine. I turned stereo on and everything was fine then all of a sudden the battery light flickered, the voltage dropped to 12.4v. 1 mile later 12.3v, another mile later 12.2v, another mile later 12.1v, I think you get the idea. I get home let it idle with the lights off and I'm down to 11.8v.
The battery is on charge ready for the morning.
I've checked the battery clamps, I've checked the battery jump point by the drivers strut, I've checked the connection to the back of the alternator. I've tested the voltage from the engine to the body to see if the earth strap was broken, but I got a reading of 0.2mV which I believe means the engine IS earthed correctly. I've plugged up INPA and aside from the suspected low voltage codes, nothing untoward.
The forums/threads I've read tell me that people have problems with the battery light being off at low rev's and coming on at high rev's but my problem seems the opposite.
I'm thinking brushes? Please help.