Dim Lights - Electrical Problem

[azhar_akbari]

Hi, I have Accord 2002 SE and I am experiencing an electrical problem. When I turn on the defogger or the blower, I see the lights get dim. It happens all the times no matter if I am idling or cruising. Can it be the alternator problem?

[mpumas]

Could be. It could also be a loose connection in a fuse box or damaged wire or connector. The question is how dim? You need a volt meter to do some trouble shooting. The defroster and blower are fused at 40A and 30A off the 80A main fuse. The headlights are fused at 20A on each side also off the 80A main fuse. So if the lights go dim when the blower and defroster are turned on, look to the 80A main fuse.You could be losing voltage at that point. Check voltage on both sides of the fuse both with load and no load. Get back to us with your results.

[lorunner]

On those cars there is what they call an ELD what it does is basically only provides the car with what power t needs from the altenator. So basically if the car is running and there is no draw the altenator is in a kind of sleep mode. Thats the best i can describe it. As you turn on accessories the ELD calls for more power and the altenators output increases. So what you are experiance is more than likely normal. It all depends on what your deffinition of dim is.

[mpumas]

lorunner-I know you are the expert on Hondas and I respect your advice. I have a question on the ELD. I see it as a current measuring device. If it detects a high current draw, I think it sends a signal to the ECU telling it to increase engine speed which in turn causes the altenator to increase voltage/current output. Is that the way you understand it?

[AccordCodger]

Good grief - that would make you accelerate when you didn't want to, just by turning on the rear window defroster. I DON'T think so!

[lorunner]

Partially. The ELD which is located in the under hood fuse box does send a command to the PCM and the PCM switches the altenator between high and low output. It doesn't however raise the engine speed. Like AccordCodger commented on the car would take off unespectidly if that happend. The way it switches from high to low is by the voltage regulator inside the altenator. Not by engine speed.

If anything as the engine speed increases the output decreases. and vise versa

[mpumas]

The increase in speed is small, only about a hundred or so RPM, just enough to keep the engine from stalling from the extra load from the alternator when idleing. And there is a connection from the voltage regulator to the ECU which does what you says it does.