Mediator7

I recently bought a 2005 C6 base auto and the high beam headlights, front side markers, and foglights do not come on under any light or switch settings. All the bulbs are standard oem styles. I replaced the relays ( 4 were pretty discolored) and fuses with ac delco units, plus I checked all the bulbs. They all worked for a minute or so then after I swapped the relays around a bit and tried again they did not work again. I rechecked the relays and fuses but no change. Also, i do hear a relay "click" when turning on the low beams manually but no sound from the fogs activation or high beams. So any idea why they didnt work, then worked for a moment, then didnt work again? Ive researched here a bit and have seen advice to check connections, possible fuse block failure, and possible switch failure. Before I go buying fuse blocks and switches, does anyone have any other suggestions by chance? Please HELP. Lol

4SUMERZ

It could well be the steering wheel turn signal multifunction stalk that is faulty.
Here is the headlight circuit which includes the fog lamps etc.
They use diffeent ground wires, so that is not likely the cause.

Good Luck

Mediator7

Thank you. Ill def put this to use and try to track down the issue.

Mediator7

Anyone else had this problem before?

Mediator7

So I have tried to interpret and understand this diagram and its a bit evasive. Anyone more capable?

4SUMERZ

I'm not certain what is not clear about the schematic. The top portion shows the fuses (engine fuse box) that power up all the lights in question.
The light circuits have a ground marked with a G designation ie: G101
The ground for SP101 or SP102 means that this is a slice in the wiring harness that connects many of the circuits, and they have a common ground point. These Ground points locations are marked on the schematic.

The issue that you have with the high beams, fog lamps and side marker lights not working is somehow connected either by the common multi-function switch on the steering column (they have been known to go bad)or possibly a common ground point not making proper contact, etc.

Looking at the schematic, and assuming all the fuses are OK, and all the wiring is in good condition, then look for a common ground for the circuits that you have issues with.
The Right High beam headlight and the fog light relay share a common grounding point G102 on the right frame rail. The ground for the relay would control both fog lamps.
Now, the Left High beam does not share that same ground point -G101 on the Left frame rail, so a bad ground for those 3 separate circuits can most likely be taken out of the equation as the issue as they have separate grounds.
The front side marker lights use separate ground points from left and right, just like the Headlights and fog lights.
It's unlikely that both grounds would be bad, but easily checked.

That leaves really the multi function switch as the only common connection to the 3 separate circuits. The Multi-function switch is grounded using G201 found at the base of the Left A pillar. That could also be checked to make sure that is OK.

Here are the circuit operation:

High Intensity Discharge (HID) Low Beam Headlamps

The headlamps may be turned ON in 2 different ways:
When the headlamp switch is placed in the ON position, for normal operation
When the headlamp switch is placed in the AUTO position, for automatic lamp control (ALC)
Battery voltage is applied at all times to the coil and switched side of the low beam relay. Ground is applied at all times from G201 to the turn signal/multifunction switch. When the turn signal/multifunction switch is placed in the HEAD position, ground is applied from the turn
signal/multifunction switch through the headlamps ON signal circuit to the body control module (BCM). The BCM applies ground to the headlamp low beam relay control circuit. This energizes the low beam relay, closing the switched side and applies battery voltage to the LEFT and RIGHT LOW BEAM fuses. Battery voltage is then applied from the fuses, through the low beam voltage supply circuits to the ballast in the headlamp assembly. When battery voltage is applied to the headlamp ballast through the low beam voltage supply circuits, the ballast charge the starter to start the lamp. High intensity discharge (HID) headlamps do not have filaments like traditional bulbs, instead the starter uses a high voltage transformer to convert the input voltage into a higher
voltage. This increased voltage is used in order to create an arc between the electrodes in the bulb.
Ground is applied from G101 for the left headlamp and G102 for the right headlamp.

High Intensity Discharge (HID) High Beam Headlamps
Battery voltage is applied at all times to the coil and switched side of the high beam relay.
Battery voltage is also applied at all times through the coil side of the low beam relay to the low beam relay control circuit, to the turn signal/multifunction switch. When the turn signal/multifunction switch is placed in the high beam position, battery voltage is applied through
the headlamp switch high beam signal circuit to the body control module (BCM). The BCM applies ground to the headlamp high beam relay control circuit. This energizes the high beam relay, closing the switched side contacts, applying battery voltage to the Left and Right High Beam Fuses. Battery voltage is then applied from the High Beam Fuses through the high beam voltage supply circuits to the left and right high beam headlamps.
Ground is applied from G101 for the left high beam headlamp and G102 for the right high beam headlamp.

Front Fog Lamps
Ground is applied at all times at G201 to the front fog lamp switch inside of the turn signal/multifunction switch. When the front fog lamp switch is placed in the ON position, ground is applied through the front fog lamp switch signal circuit to the body control module (BCM).
The BCM applies battery voltage through the front fog lamp relay control circuit to the coil side of the fog lamp relay. Battery voltage is applied at all times from the FRT FOG LP fuse to the switch side of the FRT FOG LP relay. When the relay is energized, the relay switch contacts close and battery voltage is applied from the FRT FOG LP fuse, through the relay switch contacts, to the front fog lamps. Ground for the front fog lamps is applied at all times at G101 for the left fog lamp and G102 for the right fog lamp. G102 also serves as ground for the coil side of the FRT FOG LP relay.
The BCM will send a message via class 2 serial data to the instrument panel cluster (IPC) to enable the front fog lamp indicator. The front fog lamps will deactivate when either the flash-topass or the high beam headlamps are turned ON.

Park, Tail, License and Marker Lamps
Battery voltage is applied at all times from the PK LAMPS fuse to both coil and switched sides of the PARK LAMP Relay located in the underhood fuse block. Ground is applied at G201 to the turn signal/multifunction switch at all times. When the headlamp switch is place in either the HEAD or PARK position, ground is applied to the park lamp relay control circuit. This energizes the PARK LAMP Relay and applies battery voltage to all park, tail, license, and marker lamps.
Ground for the front park and marker lamps is supplied at G101 for the left and G102 for the right. Ground for the license, tail, and rear side marker lamps is supplied at G302.

Turn Signal Lamps

Ground is applied at all times at G201 to the turn signal/multifunction switch. The turn signal lamps may only be activated with the ignition switch in the ON or START position. When the turn signal/multifunction switch is placed in either the TURN RIGHT or TURN LEFT position,
ground is applied to the body control module (BCM) through either the right turn or left turn signal switch circuit. Battery voltage is applied at all times from the BATT MAIN 3 fuse to the BCM. The BCM then applies a pulsating voltage to the front and rear turn signal lamps. Ground
for the left front turn signal lamp is supplied at G101. Ground for the right front turn signal lamp is supplied at G102. The left and right rear turn signal lamps are supplied ground at G302.

It's difficult to diagnose or troubleshoot over the ionternet, but maybe you will get it sorted out.

Good luck

Mediator7

Thank you for all that. I know that took a moment to type. Me and wiring diagrams have an uneasy relationship. Ha but im going to check the grounds. I fear it could be the fuse block but if the grounds are good, im going to probably try a multi-switch. Will update..

Mediator7

Also, now that I see that a body control module is involved I can only assume its a possible weak or failure point.

Mediator7

Okay update on this problem. I have installed a new multifunction switch but still have no high beams or fogs. I have also aquired a low mile used junction box that Im going to install next. Hopefully this solves the issue. Up until now all relays, fuses, and bulbs have checked out good. No corrosion has been noted anywhere. If anyone has any ideas please share. Thank you.

Mediator7

Hopefully this is the final update. I replaced the underhood junction block and problem solved. Foglights and High beams now work. I noticed the original box had been previously taken apart (bolts unswedged). I can only assume the previous attempt to repair or determine the problem was unsuccessful or didnt last. Either way all works for now. Feeling a little relieved.

HeliPilot27

When you say junction block, are you referring to the fuse/relay block? Still working?
Thanks!

Mediator7

Yep the large fuse block on the right fenderwell. I replaced it with a good one and all immediately worked correctly. Once I pulled the old one out I saw where some attempt had previously been made to fix the problem which failed apparently. Not long after this some little pothead druggie kid hit us and totaled the car. But it was working up until then.

HeliPilot27

Thanks for the reply, sorry about the car, that sucks! I am having similar issues so I probably beed to find a new junction box as well.
Thanks again!