Alternator Testing?
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Senior User
Joined: Jan 2005
Posts: 356
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Alternator Testing?
Hi Guys,
My battery idiot light came on last night- battery is new, on these newer vehicles can you still test the alternator by disconnecting the battery? If not what it the correct way to test if its working ok?
thanks in advance
My battery idiot light came on last night- battery is new, on these newer vehicles can you still test the alternator by disconnecting the battery? If not what it the correct way to test if its working ok?
thanks in advance
Postmaster
Joined: Jan 2003
Posts: 4,417
Likes: 3
From: Durham, NC
Absolutely not!!! Don't ever disconnect the battery with the engine running!!
Large voltage spikes can be created (from Di/Dt), which will feed into the electrical system killing expensive electronic components like PCM, etc. ..
In addition to large voltage spikes created by Di/Dt, the alternator itself creates voltage spikes, which are normally filtered by the battery. The alternator can be tested by measuring the battery voltage with and without the engine running, and by turning on electrical accessories with the engine running. Without the engine running, the battery voltage will be 12.6V-12.8V
(after setting for awhile, allowing surface charge to dissipate), and the running voltage should be 13.6V to 14.2V.
Large voltage spikes can be created (from Di/Dt), which will feed into the electrical system killing expensive electronic components like PCM, etc. ..
In addition to large voltage spikes created by Di/Dt, the alternator itself creates voltage spikes, which are normally filtered by the battery. The alternator can be tested by measuring the battery voltage with and without the engine running, and by turning on electrical accessories with the engine running. Without the engine running, the battery voltage will be 12.6V-12.8V
(after setting for awhile, allowing surface charge to dissipate), and the running voltage should be 13.6V to 14.2V.
Fleet Owner
Joined: Jan 2004
Posts: 26,007
Likes: 575
From: Brentwood,CA
Originally Posted by txplayboy001
That still works on the newer vehicles.
that test should never be used even on older vehicles. Its a stupid idea which will ruin the PCM or ECU in newer cars.
Hotshot
Joined: Jul 2005
Posts: 11,931
Likes: 180
yea guys, dont disconnect the battery. get a votl meter and measure the battery to be 12.5 volts not running. start the mtoor and you will see 14 volts at the battery terminal (alternator charging). stop buy any shop and they can do it in 5 minutes. dont disconnect the battery to test.
