Alternator? or Transmission? Confused..need a little advice here

[mellobudd]

Hi there fellas, weird thing happened to my 2005 SL a month back. I was travelling on the highway (110kph/68mph) when I noticed the airbag warning light flashing, ignored, I continued another 30mins of driving when all of a sudden the car felt like it was loosing power and wont accelerate at all! Like, it ran out of gas or something. Then I noticed the CEL light on together with the airbag warning light. Thankfully, I was able to pull over to the emergency lane and tried to start the car but it wont. Called the tow, and a couple of friends to bring a porta charger. Charged the battery and the car started but wont accelerate. I'm starting to worry that it may either be the transmission, or the alternator. A mechanic friend tested the alternator and battery and they were throwing low voltage, around 10 i think. Bought a new battery and car starts fine and brought the car home. Now the car will start and run but it looks like it is draining the new battery so he had the alternator tested while the car is running, alas, the alternator it throwing low voltage so I got a new alternator and just waiting to have it installed. Question is why the airbag warning light flashing again? I just replaced the sensor a while back the first time it went off. Could it be transmission related? Car has about 120,000 (194,000) miles on it. Thankfully I have another car to go around. Im just worried about the extended warranty on the transmission because of the milage. Thanks in advance!

[Pilgrim]

Did you read the owner's manual on this topic? Many cars flash warnings at you if the voltage drops below allowable levels. When you see odd lights on the dash, your owner's manual is the fastest and most helpful reference you can get.

No, based on your description it's not the transmission - it's the alternator.

For future reference - any time the car is running, if you put a voltmeter across the battery terminals it should show at least 14V. With the car not running, it should show about 12.5V. If it shows less that 12V you have a dangerously low battery and you should find out why - chances are that the battery is failing.

[mellobudd]

I did my research here in the forum, but there are so many possibilities and issues that almost but never the same as mine. That's why im asking the veterans to see if theres any one in here that had the same issue? However, it's just good to know that its the alternator. I kind of read somewhere here that the supplemental airbag warning light and something else could possibly be inclined with the transmission failing. I might be wrong but i swear I saw that topic here. Anyways, thanks for the reply and looking forward to install the new alternator!

[njjoe]

mello-

The air bag control module is sensitive to low voltage. Having a bad alternator and a discharged battery can create the condition that will trigger the airbag warning light.

-njjoe

[Pilgrim]

Originally Posted by mellobudd

I did my research here in the forum, but there are so many possibilities and issues that almost but never the same as mine. That's why im asking the veterans to see if theres any one in here that had the same issue? However, it's just good to know that its the alternator. I kind of read somewhere here that the supplemental airbag warning light and something else could possibly be inclined with the transmission failing. I might be wrong but i swear I saw that topic here. Anyways, thanks for the reply and looking forward to install the new alternator!

As a follow-up to my earlier email, I suggest that you idle the car and check voltage between the battery's + and - terminals with a voltmeter. I'll bet you can confirm your alternator diagnosis by observing that the system isn't running at 14V or slightly more.