2003 Saturn Vue Dimming Headlights

Greetings all, and thank you for reading this.

My 2003 Saturn Vue V-6 AWD headlights dim while driving. They don’t entirely go out, but at the very least it is distracting. It happens on both hi and low beam. The battery indicator light also pops on briefly, and generally unpredictably. The only indicator of the battery light turning on is it seems to happen more often when I come to a stop, when the fan turns on. And possibly more often while using the AC. The headlights always dim, nothing seems to make this happen more or less.

This vehicle has a new alternator. Actually, it is on its second new alternator. The first was installed in November 2014. It was overcharging and I was getting all kinds of funny lights on, before replacing it February 2015. I’ve had the current problems since this time. My mechanic has tested the alternator, starter, battery, and connections. Has also checked all the grounds. Apparently, my vehicle is 100%?

While the dimming lights don’t really bother me, I have a teenager who wants to inherit this vehicle. I would like to resolve this before passing it on. I would appreciate any advice.

thank you

Have u replaced the timing belt yet? Just asking

Your alternator is controlled by the ECM. So when you let up on the gas the alternator is supposed to output more to compensate. It sounds like this is not happening. I would check the ECM input to the alternator. If that is good I would get a New alternator, not a remanufactured one.

Try replacing the battery cables + and -, you may have corrosion on them giving you a bad connection. With the age of the car it is not worth cleaning them, just get new ones,

The battery light turning on means that something is not right with the charging system but you most likely realize that. You stated that the current issue happened near or at the same time the alternator was replaced so my thinking is that the replacement alternator has an intermittent problem. Other things like the vehicle wiring and the ECM, as @knfenimore pointed out, are involved with the charging circuit and could be causing the problem but my bet is on the alternator. Even though things were tested it appears that the problem wasn’t occurring while the tests were being done since nothing wrong was found but yet there really is a problem. Intermittent issues can be tough to find at times but logical deduction points to the alternator since the problem wasn’t happening before the replacement took place.

How old is your serpentine belt? It could be slipping.

Thank you all for your comments. To answer a few questions both my timing belt and serpentine belt were replaced at the 150,000 mile tune up, I will check to make sure the serpentine belt is tight. I can’t actually get at the timing belt without removing more of the engine than I have tools for. I will change the battery cables, they are original and its time. Its not clear to me what is involved in checking the ECM. My mechanic doesn’t appear to be aware of a way to check this, and is reticent to replace my alternator without reproducing the problem or finding a diagnostic problem. In general, he lets my car idle in his shop. But it in my opinion it doesn’t appear to draw enough electricity to cause a light to flash while idling. He can’t see the lights flicker during the day… Any advice on what to request would be appreciated, thank you.

That is, I replaced both belts this spring when they replaced my alternator. Thank you.


My advice is to get a new mechanic

It sounds like he doesn’t even know how to TEST an automotive charging system

And if he doesn’t know that, you can be sure he doesn’t know how to diagnose and repair it

I advise you to not replace the battery cables just for the sake of changing them, because they’re old. Check if all of the connections are clean and tight, first

Unless the battery cable clamps are in extremely poor condition or have been proven to be bad somehow I don’t recommend you change them out. If you are not having starting issues those cables should be fine.

The ECU controls the charging rate current of the alternator to the battery. The voltage from the ECU varies as the required load on the battery changes. Monitoring the voltage on that lead with a voltmeter will show any changes on the lead.

Another possibility for the problem is there is just a wire problem in the wiring to the headlights. If the dash lights also dim and blower speed changes this would mean the charging voltage is varying. The charging system may be fine but since the battery warning comes on at times that again points to the alternator circuit or just a slipping belt. If the battery warning light turns off just by revving the engine slightly that may be a clue for a loose belt.

Again, all, thank you for your input.

Cougar, the lights on my dash dim with my headlights, I should have mentioned that before. It wasn’t clear to me, do you see that as evidence of a problem with the ECU? This is part of the altenator, yes?

My mechanic had asked me to step on the gas when my battery light flickers on, although I believe he was trying to rule in or out a problem with the computer system. The problem is my battery light flickers on so briefly, it isn’t possible to step on the gas to test this.

Unless there is other input, I think I will ask my mechanic to test the ECU the next time I take my car in to be serviced.

thank you

I second the motion for a different mechanic and preferably a shop that specializes in electrical problems.

I agree, a good mechanic would be a God send. I don’t seem to have a lot of those in my area. It is very much my experience that mechanics here like to replace parts and if that doesn’t work they shrug their shoulders. I find myself diagnosing more and more problems with my car, because I can’t find someone to at any price…

@db4690 is spot on, what’s needed is to test the charging system, not the individual components. There almost certainly has to be something wrong with the charging system if the battery light is coming on in normal operation.

Let’s say for sake of argument that your mechanic is 100% right, there’s nothing wrong with the charging system and/or battery. Then the only conclusion possible is that battery light must be coming on b/c there’s something wrong with the light or the circuit that lights it, and doesn’t represent a problem other than that. So let’s make that assumption.

BTW, this all could be verified if you had your mechanic hook up a voltage meter to the battery you could monitor as you drive around. The voltage should hover around 13-14 volts with the engine running, and never go below 12 volts at all, except briefly during cranking to start the engine.

So if there’s nothing wrong with the battery and charging system, what’s causing the headlights lights to dim? It could be the headlight bulbs are bad. More likely, the sockets the bulbs connect to are corroded. Other possibilities are high resistance connections somewhere between the battery and the headlights. for example, if a relay is involved in the headlight function, the relay could be bad. Or the ground connection between the bulb sockets and the chassis could be corroded and failing.

I doubt the trouble is with the ECU or the wiring but it is possible. My money is on the alternator, even though it was replaced. It may have been a rebuilt and had an intermittent problem that was missed on the checkout.