Ok so while i was using mpps to read my map, mpps shows my battery is 19.3v ... it should be 12v right?

 

 - Would this be a dodgy alternator?

Is that while running of just ignition on?

The battery is 12.6v and should go up to around 14v with the alternator going.

Either way, if the reading is correct, that's crazy high.

All you need is a working DVM/DMM and check the battery voltage with engine not running and again with the engine running at idle, and again running at about 3000RPM.

I'd expect regular bulb failure and battery boiling up its electrolyte if it was seeing 19V coming its way regularly.

Just to confirm, battery voltage should be a nominal 12 volts.

Edit:- Also, when charging, as above, battery volts max should be 14.6 volts - I think, alternator is rated as a 14 volt regulated output.

Edited 9 May, 201511 yr by rum4mo

I don't believe that reading.

I don't believe that reading.

+1 even an overcharging alternator shouldn't be that high

that just on ignition, but if the alternator was goosed isnt it possible to give weird readings? Idont mean over charging, i mean what ever is responsible for volt measure off the alternator.

The alternator doesn't hold voltage like that.

Basically... Check the voltage properly and report back. Until then forget it really, it will just be an error.

ok, but its a bit dodge when i come to flashing the ecu... as i need to make sure its a solid 12v :P

I'd go out and buy a cheapo DVM. I've got four. One I got from an old employer(we suspect he got these with an order of dodgy cable) , another a a present from my kids. One other was road kill from possibly the top of a BT van ,and the best a top of the range FLUKE from old employment. All read very similar, so for car work, there's no reason to splash the cash. If in doubt of accuracy- go to Maplin and buy a 9.1v Zenner diode and a 1000 ohm resistor. Connect one end of resistor to +ve of a car battery and join diode to resistor and other end to -ve. In one configuration ,you wil get a reading on the volts range of approx .7v, and if diode reversed of 9.1v. (approx). ( USE 20V range). Meter is now calibrated , as near as needs be. Now try it on the battery reading 19v. If any ore than 16v- TURN OFF ENGINE AND GET OUT. COME BACK WHEN BATTERY IS COOL.

As a few people have pointed out.

A 12v battery isn't going to read over 19v Is it?

Alternator isn't going to put out much over 14 max, so it's a false reading or something.

A few folks did point it out, but how many know that a simple test of the older dynamo was to disconnect the output and field coils from the car electrics, short the output to the field coils and use a mains Lamp across the output to deck. If all was well ,the lamp would light ( that means output is close to 220v). I'd not discount high voltage on an alternator, so if battery was warm or hot, I'd check voltage on charge. ( BUT CAREFULLY)

19V plus, if correct, would mean that the regulator was at least 200% FUBAR!! And as well as blowing bulbs and boiling the battery, certainly would kill pretty much all the electronics.

 

Buy a cheap multimeter (you can get one that's good enough for about £6), put it on the 0-20v scale, and take readings across the battery terminals engine off (expect 12v) and engine idling, main electrics off (expect about 14.4v).

As above^^^^^^^^^^

 

You need a good multimeter for most DIY car work, spend on a good one to last you a while, invaluable tool to have................I buy circa £80 ones which do me.........