Hi folks,

I've searched the forums for a possible answer to my problem, but could not find anything related. We purchased used 2008 Honda Accord Coupe for our 16 yr son. The passenger high beam headlight is not working. The bulb is fine, as I have swapped both high beam bulbs to each side. Both bulbs work on the driver's side, but not the passenger side. I'm getting 12 volts at the passenger high beam connector when the car is just sitting parked with no lights on (strange). The voltage does not change when actually turning on the high beams. The drivers side has zero volts with high beams off and 12 volts when turning on the high beams. I've check both fuses in each fuse box inside the car and all 4 fuses are good. I obtained a copy of the electrical drawing for the head lights, but there is no information regarding the "high beam control circuit". Any help would greatly be appreciated.

 

How the Headlights Circuit Works
The Headlights circuit is composed of the Driver’s MICU, the Passenger’s MICU, the Headlight Switch, the Dimmer/Flash-to-Pass Switch, the Left and Right Headlights, and the High Beam Indicator.
The Driver’s MICU and Passenger’s MICU control the Headlights with built-in Low and High Beam Control Circuits based upon the position of the Headlight Switch and the Dimmer/Flash-to-Pass Switch.
The Driver’s MICU and the Passenger’s MICU communicate Headlights information directly between each other and via B-CAN.

High Beams
When the Headlight Switch is moved to the ON position with the Dimmer/Flash-to-Pass Switch in the HIGH position, ground signals are supplied to terminals R8 and R22 of the Driver’s MICU.
The Driver’s MICU and the Passenger’s MICU activate their Low and High Beam Control Circuits, supplying battery voltage to the Low and High Beam Headlights, causing them to come on.

 

Thank you tech8 for the explanation of how the control circuit works. Since I'm seeing 12 volts at the passenger high beam connector pins when the car is parked and lights turned off, does that mean the driver's MICU is the problem since it supplies the ground signal? Also, why isn't that high beam staying on constant? That's what really has me confused. I forgot to mention, I did test the black negative of the connector to the chassis and did have continuity with all the lights off. Any suggestions on what to test next or solution to the issue is greatly appreciated.

 

When you measure voltage on the orange wire, are you touching the voltmeter's black lead to the connector's black wire or chassis ground? Are the measurements the same?

If you're seeing approximately 12 volts at the orange wire with headlights off, it can possibly be an issue with the passenger MICU or wiring; such as a short.

 

I was testing both pins in the connector and had 12 volts with all lights turned off. I did test the voltage on both sides of each fuse on the passenger side fuse box (neg to chassis) and had 12 volts there also.

 

That's unusual that the high beam bulb doesn't light up if there is 12 volts and ground at the orange and black connector wires.

If remove passenger side Fuse No. 1 (10A), is there still 12 volt at the orange wire?

 

I thought it was strange also. Unfortunately, I'm offshore working and won't be able to perform any further testing until I get home. I can possibly ask my father-in-law to test that for me. Any other test you would done if I can get him there to test for us?
Thanks a bunch for your help!

 

I would try a battery cable reset first. See my posts #8 and #9 in this other thread: https://honda-tech.com/forums/honda-...oblem-3323865/

 

We recently upgraded his stereo and amp, so we disconnected the battery a few times. Is it possible that's what caused the multiplexes to be out of sync? The car already had an after market stereo in it. It was just an upgrade.

The video in the thread with #2 battery reset procedure is unavailable. Is there another video or can you explain the procedure?

 

Refer to this:

 

I removed the #1 fuse and there was zero volts on the orange wire. I also checked the voltage of orange wire with the fuse in and had 12.5 volts with the negative lead of the volt meter on the black wire pin (in the plug) and also with the negative lead of the volt meter to the chassis. I also performed the 15 minute battery cable reset and the 10 minute (with key on II). Still no passenger high beam light. Any suggestions is greatly appreciated. Thanks

 

Whenever you're taking voltage or current readings,the subject in question should always be loaded. In this case, plug in the connector to the high beam, turn on the high beams, and then take your readings,by back probing the connector or piercing the wire. (also make sure to connect the black lead of your meter to a suitable chassis ground)

My guess is you will not have 12v on the orange wire with it connected to a powered bulb.

 

Correct, zero volts with bulb in connector and high beams turn on. Would this suggest the passenger MICU needs to be replaced? If so, who do you guys recommend ordering from and where can I find the part #? Thanks!

 

Not just yet. With everything connected the way I told you above,you need to check the ground wire of the bulb. Should read .03v or less.

Also you need to use your wiring diagram and find and test power supply for the bulb directly at the MCU connector(I dont know which one,I dont have the diagram in front of me)

Im working so I may or may not answer today. I ll try to get on when I can.

 

Sorry for the delay. My work schedule offshore and when I can get access to my son's car is crazy. I've checked the ground wire of the bulb to the chassis and had 0.00 to -0.0003. I'm not sure what power supply / MCU connector you are mentioning to test. The only drawing I have is this one. Any additional information on what to check next is greatly appreciated. Thanks!