It's the alternator, right?
Thread Starter
Burning Brakes
Joined: Jun 2004
Posts: 860
Likes: 0
From: Birmingham AL
It's the alternator, right?
Hey Everybody--
Not a huge problem, but could become worse I suppose: when driving at night and I let off the gas and/or hit the brakes, I notice the headlights dimming a significant amount. Not to zero light output, but a substantial drop from normal brightness. This car is a 2002 coupe, has 160K miles on it, and has the original alternator, as far as I know. I have one w/ far less miles handy from a part-out, so I'll probably just swap that one in. But can anyone tell me if that sounds like the alternator might be the culprit?
Thx,
Fred
Not a huge problem, but could become worse I suppose: when driving at night and I let off the gas and/or hit the brakes, I notice the headlights dimming a significant amount. Not to zero light output, but a substantial drop from normal brightness. This car is a 2002 coupe, has 160K miles on it, and has the original alternator, as far as I know. I have one w/ far less miles handy from a part-out, so I'll probably just swap that one in. But can anyone tell me if that sounds like the alternator might be the culprit?
Thx,
Fred
Team Owner
Joined: Jul 2006
Posts: 22,167
Likes: 4,172
From: Kannapolis NC
I doubt it's the alternator. Did you measure the output across the battery with the engine running with a meter? It's normal for the lights to dim when you hit the brakes or the power window switch, but if it's dimming more than usual, you probably need to clean up some connections and grounds. I'd check very carefully the battery connections including the red cable from the battery to the starter solenoid lug. That one ties the battery and alternator together and is commont to corrode or get loose. When you are driving and monitor the voltage on the DIC, does it vary greatly, like 12v up to 15v for no reason? If so, once again, I'd check the same connections.
Burning Brakes
Joined: Jun 2003
Posts: 1,079
Likes: 1
From: Niagara Falls ON
What kind of battery do you have? If it is an Optima make sure that you have it fully charged with a charger that is designed for those batteries..Ctek will do the job.
That is, if you have that type of battery.
That is, if you have that type of battery.
Thread Starter
Burning Brakes
Joined: Jun 2004
Posts: 860
Likes: 0
From: Birmingham AL
I doubt it's the alternator. Did you measure the output across the battery with the engine running with a meter? It's normal for the lights to dim when you hit the brakes or the power window switch, but if it's dimming more than usual, you probably need to clean up some connections and grounds. I'd check very carefully the battery connections including the red cable from the battery to the starter solenoid lug. That one ties the battery and alternator together and is commont to corrode or get loose. When you are driving and monitor the voltage on the DIC, does it vary greatly, like 12v up to 15v for no reason? If so, once again, I'd check the same connections.
Fan belt? Fans ain't got no belt! :P If you mean the serpentine belt, tension is fine there.
Thanks guys,
FT
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
I doubt it's the alternator. Did you measure the output across the battery with the engine running with a meter? It's normal for the lights to dim when you hit the brakes or the power window switch, but if it's dimming more than usual, you probably need to clean up some connections and grounds. I'd check very carefully the battery connections including the red cable from the battery to the starter solenoid lug. That one ties the battery and alternator together and is commont to corrode or get loose. When you are driving and monitor the voltage on the DIC, does it vary greatly, like 12v up to 15v for no reason? If so, once again, I'd check the same connections.
The very first place to start is at the major power connections in the charging / starting system. The starter solenoid is a major source of trouble if not properly clean and tight:
The BATT terminal on the back of the alternator needs to be clean and tight.
The battery cables/terminals MUST be torqued to 11 ft/lbs to make proper connection with the battery.
The ground connections on our cars are another major source of electrical turmoil. G-101, 102, 201. 202, 301 & 302 are connector type grounds and can get corroded on the pins INSIDE the connector and compromise those connections.
G-101, 102, 201. 202, 301 & 302 Look like this:
G-101 & 102 are the worst offenders as they are exposed to the elements and those connectors are NOT water tight!!
Ground locations:
G-104/108 is the main chassis to battery ground wire and must be clean and tight for proper component/module operation:
Bill C
Le Mans Master
Joined: Nov 2005
Posts: 6,993
Likes: 25
Hey Everybody--
Not a huge problem, but could become worse I suppose: when driving at night and I let off the gas and/or hit the brakes, I notice the headlights dimming a significant amount. Not to zero light output, but a substantial drop from normal brightness. This car is a 2002 coupe, has 160K miles on it, and has the original alternator, as far as I know. I have one w/ far less miles handy from a part-out, so I'll probably just swap that one in. But can anyone tell me if that sounds like the alternator might be the culprit?
Thx,
Fred
Not a huge problem, but could become worse I suppose: when driving at night and I let off the gas and/or hit the brakes, I notice the headlights dimming a significant amount. Not to zero light output, but a substantial drop from normal brightness. This car is a 2002 coupe, has 160K miles on it, and has the original alternator, as far as I know. I have one w/ far less miles handy from a part-out, so I'll probably just swap that one in. But can anyone tell me if that sounds like the alternator might be the culprit?
Thx,
Fred
You could take the alternator in to have it tested but I've seen PLENTY of alternators that tested good that were not. The only good way to tell is with a scope to see how clean the DC coming out really is.
Last edited by dougbfresh; May 3, 2012 at 04:19 PM.
