2007 V8V . ended up out last night after dark and found that the high beams will not "latch" on . the high beams work but the only way to keep them on is to hold the stalk toward you with your finger . Any suggestions , quick fixes ? Tks everyone .

 

Same switchgear as the Volvo I believe. If the lights are switched off and come on automatically the highs won't latch, however if the main switch is set to on they will latch.

 

Maybe that's the answer , It was light when I went out so I just let the lights come on in auto . Tks for the tip I will try the lights in manual and see if that's the issue .

 

The programming for Canadian DRLs means that if you're in the off position, the high beams won't latch, but you should still be able flash the brights by pulling the stalk.

If you do change to the "lights on" setting, your headlight washers will activate when you use the windscreen washers. I always leave mine in the off position unless I need the high beams. I really hate the headlight washers messing up an otherwise fairly clean car.

 

So I may be wrong, but I thought you push the stock forward to turn the high beams on, and pull towards you to flash them.

 

This is the correct answer . they do latch on with the headlight in the on position .

 

I'm bringing up this older thread because it accurately describes how the headlight high (main) beams should function. For the high beams to remain illuminated, the headlight switch must be on, otherwise, pulling the control stalk back will only cause the high beams to flash.

In my case, even with the headlight switch in the ON position, the high beams won't remain latched in the continuously ON position, but will only flash when the lever is pulled to the rear.

To troubleshoot the issue, I located in the Workshop Manual for the DB9, Circuit Sheet 33 on page 18-1-62. This diagram indicates the latching function is controlled by Relay R8 which is located in the CEM (Central Electronic Module). The obvious solution would be to replace this relay, but...

In the same manual, the CEM Fusebox Sheet 7 on page 18-1-27 contains the following: "NOTE Relay 18 Comfort and Relay 15 Fuel Pump are the only accessible interchangeable relays. All other relays referred to are internal to the CEM."

Apparently. the CEM contains a number of relays that can't be changed. This would affect a number of systems. Is there any solution other than replacing the entire CEM?

I further note that the Underbonnet Fusebox has this note - "Relays 1-8 are replaceable, above that are not."

How are relay problems in these areas repaired?

 

@KOCF
I would assume the fault was in the switch 'MAIN BEAM' in the Switch indicator , or in the 'PROFET' in the Switch-Master Light. Check the voltages on the C0036-7 and C0036-8 cable connectors to pinpoint. They should be =0 for a latched high beam.
Names and numbers ref to page 18-1-62.
Good luck.

 

Hi Agaton
Thanks for your insight. The car is new to me, and this is my first adventure chasing sparks in a DB9.
Reference page 18-1-62, I know that the Switch-Master Light must be in the DIP position for the high beams to latch on rather than only flash. The only way I can keep the high beams illuminated is to continuously hold the Switch-Indicator lever in the high beam position. This gets old quickly.

Since the high beams do flash with the Switch-Master Light in any position, as they should, when the Switch-Indicator (which is the turn signal stalk or lever) pulled to either MAIN BEAM or FLASH TO PASS positions, then C0036-7 must be powered or the high beams wouldn't flash.

It looks to me that relay R8 in the CEM is the latching relay that receives power from the high beam transistor which when proper logic conditions are met, closes this latching relay, thus allowing CEM bus 2 to power the high beams. I think that either the transistor is defective or not getting power or the relay has failed.

I've attached the 18-1-62 schematic we've been discussing with components highlighted as well as a photo of the CEM fuse panel.

My puzzlement is, assuming relay R8 is bad, or I just want to change it to eliminate it as a cause, how is it possible to access the components inside the CEM?

The CEM does not look like a field serviceable item and would certainly be very expensive to replace. Anyone have knowledge of this?

 

Hi.
First I should state that I have assumed that the switch gear is the same as in my Vantage, i.e. the 'Switch indicator' itself is latching. First complete pull latches, the next releases etc. Therefore there in no need for a 'latching relay'. I interpret the schematic as follows: R8 supplies power to the main beam. R8 is activated via CEM electronics either by the 'flash' function (C0036-7 grounded via C0036-6, and this is independent on other light switches), or by the 'MAIN BEAM' switch (C0036-7 grounded via C0036-8).
This second case requires that the 'MAIN BEAM ENABLE' has a GND potential. This is supplied via the MOSFET if the 'Switch-Master Light' is in a suitable position (DIP?)
Note that R8 will activate if C0582-31 is _grounded_ , not the reverse.
I have no idea how the CEM is serviced. My guess would be replacement like most other parts.

PS-This may be a stupid question, but have you pulled the selector all the way back? You should be able to feel the switch action (like a push-push switch). Otherwise I stand by me original recommendation: C0036-8 should be GND in DIP mode or the 'Switch Master Light' is broken. If that is ok, C0036-7 should be GND in main beam mode or the 'Switch indicator' is broken.

 

Agaton:
I believe you have discovered the problem. Both your Vantage and my DB9 use the same 4G43-37-10907 "Switch-Indicator Steering Column", except mine does not latch. I assumed it was made this way, hence the need for the latching relay. Since yours does latch mechanically in the high beam position, it looks like mine is defective and I just need a new switch. Thanks very much.