To accurately check the voltage regulator on the vehicle,
the belt, auto-tensioner and all pulley driven accessories must be in proper working order and the battery fully charged!!!
On vehicle test procedure:
- Engine off and all accessories off.
- Use an Amp meter to verify no significant parasitic current loss at battery.
(There may be a few milli-amps for the radio presets, clock etc.)
- Briefly turn on the headlights (10 seconds) to remove any surface charge.
- Connect a volt meter to the fully charged battery (13.0 - 13.4 volts).
- Run the engine at 2000 rpm.
- The volt meter should read steady between 13.5 and 15.0 volts.
- Turn on: High beams, heater fan on high, radio up loud and rear defroster (if you've got one.)
- The volt meter should read steady between 13.5 and 15.0 volts.
As to the
auto-tensioner, there is no adjustment. It correctly tensions a correctly installed, proper length belt; or it's got a weak or broken spring and you replace the entire auto-tensioner assembly.
Most GM auto-tensioners have a tension indicator, but that's
only valid if the belt is correctly installed and the proper length. (An old belt might be stretched.) A ribbed-belt tension guage is the official testing tool, but I've yet to find a mechanic or shop that owns one. They all just rely on a mechanic's calibrated thumb and seat of the pants experience.
Short and sweet. If the tensioner doesn't feel funky/jerky when you take the old belt off, it's a near certainty the spring is not broken (at least 99.5% of the time.) If you put on a new, correct part # serpentine belt all correctly routed on the pulleys and the tension indicator on the auto-tensioner reads correctly, it's a virtual certainty the auto-tensioner is OK and the belt is correctly tensioned (say 99.99% of the time).
While you have the serpentine belt off, check the other pulleys it turns. Any pulleys that should turn freely (idlers, AC Compressor Alternator) - give 'em a good spin. Listen for noise and that they don't spin down to quickly. Idler pulleys will spin longer than AC compressor and alternator pulleys (drag from the brushes). Turn all pulleys that can be hand turned to feel for bearing roughness as you turn them. (That includes all the ones you just gave a good spin.)