8th Generation Honda Civic Forum banner
1 - 6 of 6 Posts

·
Registered
Joined
·
3 Posts
Discussion Starter · #1 ·
[ 2008 Civic LX manual] All fuses intact, bulbs not burned out, and new bulbs didn’t help. Turn signals, high beams working fine. Both low beams do not turn on. If it’s not fuses or bulbs what is it?
 

·
Registered
Joined
·
185 Posts
Did you check all the fuses? I believe there are more than one for the headlight circuit.

If the fuses are good, and the switch on the steering wheel is ok, then you'll need to trace the wiring back. Any recent work done on the car the might have disconnected something?

The MICU controls the headlights via an internal relay. If you are comfortable reading schematics, you could trace the wiring using the diagram at the link below and see where you have (or don't have) voltage. If the MICU is getting voltage but not sending out voltage to the headlights, but is getting an "on" signal from the combo switch then the MICU may be suspect.

2006 had issues with the MICU where weird things would happen. For example, one of my 2006 Civics had an issue where the LR door would not turn the overhead light on, but the other doors would yet the wiring and switch was good. Later, the immobolizer system wouldn't recognize the key, and it turns out their is a TSB for faulty MICUs. Once they replaced the MICU, the overhead light started working with the LR door. Something to do with the mulitplexer signals that are used to reduce the amount of wiring that runs throughout the car.


Good luck.
 

·
Registered
Joined
·
3 Posts
Discussion Starter · #3 ·
No recent work done. When I turn switch to low beam the car thinks the lights are on so I don’t think it’s the switch, if it was broken i.e. didn’t complete the circuit the car wouldn’t think they were on right? I’ll try checking the voltage before I bother buying and installing a new switch for it to fix nothing lol. What do you have to do to replace the MICU ?
 

·
Registered
Joined
·
185 Posts
In the underdash box, the fuses are #16,17, and 21. I'm guessing those are the ones you checked.

The MICU was replaced by the dealer as part of a TSB. They had to reprogram the keys and I didn't have the equipment to do it. Since then I've read where some people have been able to swap in a MICU from a salvage yard and didn't need to reprogram anything. I'm sure there are videos online on how to replace it, but it should be a matter of unbolting it and removing/reconnectiong a boatload of connectors (whilst kneeling on the ground with the sill plate gouging you in your stomach).

I'm not saying the MICU is your issue - I was just letting you know that the relays that turn the lights on are inside the MICU and don't appear to be replaceable. If you trace the wires and you can't find anything wrong, the MICU may need to be looked at. If you have switched power going into the MICU from the combo switch, and don't have power out of the MICU for the headlights, then I would think the MICU has some issue.

You might search to see if there is a way to reset the MICU. I know on older Accords you had to reset the power window multiplexer when you lost power, but I don't know if the Civic has some way to reset the system or not.

Good luck.
 

·
Registered
Joined
·
276 Posts
[ 2008 Civic LX manual] All fuses intact, bulbs not burned out, and new bulbs didn’t help. Turn signals, high beams working fine. Both low beams do not turn on. If it’s not fuses or bulbs what is it?
If you've checked all the fuses and they are good, the next thing to do would be to use a multimeter to check the voltage at the low beam holders with the headlight switch in low beam position. You also need to check if the ground wire from the holder is good even if you are getting 12V at the low beam bulb holders. Also suggest that you clean the clips/pins of the bulb holders with isopropyl alcohol to clear any dirt/grime buildup. This should help in most cases.

If it doesn't then the next thing to check would be headlight bulb switch on the steering wheel for any contact issues.

Sent from my SM-A505F using Tapatalk
 
1 - 6 of 6 Posts
Top