2004 Malibu Intermittant Battery Light

I have a 2004 Chevy Malibu Maxx that randomly dings and shows me the battery light.
It usually happens when going uphill or during really hard accelerations.

It is also showing OBDII code P0621.

The car has no other issues. Always starts, always runs well.


What causes this problem? Where should I start looking? I'm thinking it's probably a bad connection somewhere.

I have a 2004 Chevy Malibu Maxx that randomly dings and shows me the battery light.
It usually happens when going uphill or during really hard accelerations.

It is also showing OBDII code P0621.

The car has no other issues. Always starts, always runs well.


What causes this problem? Where should I start looking? I'm thinking it's probably a bad connection somewhere.

Check the wiring harness closely between the generator and the PCM. If it all looks ok, and if this is a V6, you can try and insulate the B+ wire from the back of the generator where it runs past the ignition module/spark plug wires. Use Nickel tape, or something comparable (the tape is a little pricy). It's possible that the B+ wire is picking up voltage from the plug wires. It's also possible there is a problem with the PCM, but since it only happens on acceleration I would lean towards something else.

Do you happen to know which pins I can check on the PCM connector?

I don't have a service manual for this car :-/

Does your vehicle have a voltage gauge? If yes, what is the voltage when your light comes on?

If the voltage is dropping, then you either have an alternator or PCM problem....

Update on this issue:

I shielded the + alternator cable that runs under the ignition wires to the battery. I used aluminum foil 4 layers thick and grounded the shield to the engine. I've checked it for proper ground using an ohm meter several times. It's definitely working.

The problem seems to happen less, but it still happens.

I installed a volt meter inside the car and watched it while I was driving. When the battery light comes on the voltage does not change at all. It's right about 15v the whole time. I'm using an analog meter, so it's hard to tell exact voltages. but it's accurate within a volt or two.

I connected the meter between engine ground ( right behind the alternator bracket ) and the + battery cable at the alternator.

I tried re-creating the problem by wiggling the wiring harness around, but have failed to do so :-/

Still looking for a solution

Update on this issue:

I shielded the + alternator cable that runs under the ignition wires to the battery. I used aluminum foil 4 layers thick and grounded the shield to the engine. I've checked it for proper ground using an ohm meter several times. It's definitely working.

The problem seems to happen less, but it still happens.

I installed a volt meter inside the car and watched it while I was driving. When the battery light comes on the voltage does not change at all. It's right about 15v the whole time. I'm using an analog meter, so it's hard to tell exact voltages. but it's accurate within a volt or two.

I connected the meter between engine ground ( right behind the alternator bracket ) and the + battery cable at the alternator.

I tried re-creating the problem by wiggling the wiring harness around, but have failed to do so :-/

Still looking for a solution

I installed a volt meter inside the car and watched it while I was driving. When the battery light comes on the voltage does not change at all. It's right about 15v the whole time. I'm using an analog meter, so it's hard to tell exact voltages. but it's accurate within a volt or two.

I connected the meter between engine ground ( right behind the alternator bracket ) and the + battery cable at the alternator.

I tried re-creating the problem by wiggling the wiring harness around, but have failed to do so :-/

Still looking for a solution

I installed a volt meter inside the car and watched it while I was driving. When the battery light comes on the voltage does not change at all. It's right about 15v the whole time. I'm using an analog meter, so it's hard to tell exact voltages. but it's accurate within a volt or two.

I connected the meter between engine ground ( right behind the alternator bracket ) and the + battery cable at the alternator.

I tried re-creating the problem by wiggling the wiring harness around, but have failed to do so :-/

Still looking for a solution

I installed a volt meter inside the car and watched it while I was driving. When the battery light comes on the voltage does not change at all. It's right about 15v the whole time. I'm using an analog meter, so it's hard to tell exact voltages. but it's accurate within a volt or two.

I connected the meter between engine ground ( right behind the alternator bracket ) and the + battery cable at the alternator.

I tried re-creating the problem by wiggling the wiring harness around, but have failed to do so :-/

According to my Haynes manual code p0621 means: alternator L-terminal circuit.
What does that mean? I don't see it labeled on a schematic anywhere in the book :-/

Still looking for a solution

Does the Horn work? The Alternator and Horn seem to be on the same circuit!

Did you change Spark Plugs with aftermarket ones? I know it sounds weird but theres info on it here http://www.hptuners.com (http://www.hptuners.com/forum/showthread.php?19767-Damage-due-to-jump-start-quot-service-charging-system-quot-P0621&;) Seem to be an issue with Vettes, but it may help you diagnose better.

Seems to be a problem with Diesel Trucks too!

I would take the Alternator out and take it to AutoZone or Advance Auto and have it tested. If it checks out good, you can move to wiring and PCM.