Calling C5 Officiandos.

[C2 VET]

I think the BCM has the program because when I switch the Twilight to on on the DIC the lights come on. I'm assuming the safety side of things is that is the sensor fails when the twilight is activated that the default setting is lights ON. When they come on in this setting you can't turn them off unless you turn the ignition off.

 

[C2 VET]

The yellow and green wires are present in C1 but disappear into the look with about 40 other wires. I’ll have to get the bore scope out and look inside the dashboard for the connector

 

[C2 VET]

I found the connector in the dashboard taped up out of the way. It looks like the car never had one but the option was always in the loom. Anyway, now my new sensor is connected the lights don’t come on in daylight when I enable the twilight sentinel on the dic the lights stay off. They didn’t come on again when I covers the sensor however. We shall see how things go when it gets dark !

 

[Frank MUGFORD]

Hi Frank

For a C5 Check at the BCM under passenger floor
As I show here is wiring to the horn and then wiring from PCM and to BCM
Check wire B10 at connector C1 and check when horn button is pushed does the BCM horn relay control circuit work

Make sure when by the BCM, Onstar network and fuse panel that no water damage of some critter liking to eat your wires

View attachment 31066

Hi Frank

For a C5 Check at the BCM under passenger floor
As I show here is wiring to the horn and then wiring from PCM and to BCM
Check wire B10 at connector C1 and check when horn button is pushed does the BCM horn relay control circuit work

Make sure when by the BCM, Onstar network and fuse panel that no water damage of some critter liking to eat your wires

View attachment 31066

Thanks for this. So far I've checked the fuse which looks OK and replaced the relay with another which I am assuming is OK but which does not, even so, prove its integrity. Following another line of thought, I'm going to check the actual horns which I understand can suffer damage from water dripping fom the retracted pop up headlamps. Yet another line of thought suggests a faulty laminar contact sheet underneath the airbag; seems there is an after market fix for replacing this.
Thanks for your learned help team Zr.

 

[teamzr1]

Thanks for this. So far I've checked the fuse which looks OK and replaced the relay with another which I am assuming is OK but which does not, even so, prove its integrity. Following another line of thought, I'm going to check the actual horns which I understand can suffer damage from water dripping fom the retracted pop up headlamps. Yet another line of thought suggests a faulty laminar contact sheet underneath the airbag; seems there is an after market fix for replacing this.
Thanks for your learned help team Zr.

You are correct in that known of water getting into the horns
How about using a multi meter probes to horn wires and watch meter while someone pushes down on steering wheel
and see if voltage appears
Also try with black probe directly to chassis in case of a ground wire issue

Or follow the ground side of horn to the ground slice pack mounted on the frame
That does pry apart, and you may find water got in and corroded the pins

 

[teamzr1]

Ground splice pack for horn

Location: Engine compartment, on top of the right frame rail, just behind the right headlight

Circuits: horn, right headlamp door, underhood lamp, headlamp door control module, fog lamps, A/C compressor clutch, AIR pump, Splice Pack 102.
Note: the stud attaching the ground tab to the frame can get corroded and easily snap off if you are not careful.

 

[Frank MUGFORD]

Hi Frank

For a C5 Check at the BCM under passenger floor
As I show here is wiring to the horn and then wiring from PCM and to BCM
Check wire B10 at connector C1 and check when horn button is pushed does the BCM horn relay control circuit work

Make sure when by the BCM, Onstar network and fuse panel that no water damage of some critter liking to eat your wires

View attachment 31066

Hello Zr1. I think I might have already responded to this but heyho! Can't find it. Thanks anyway; you are an absolute mine of information and help. This is where I think I am at the moment:-
The fuse checks out and the relay would appear to be OK. The horns speak when the emergency button on he FOB is pressed so that proves their integrity. Hence it must be the laminar contact sheet underneath the air bag in the steering wheel don't you think, unless (as you suggest could be) some munchers have got at wiring elsewhere?
I'll check the points you make regarding the BCM as noted. Regards.

 

[teamzr1]

Hi Frank
Good thinking on your part to do the FOB test says a lot about horns themselves, relays, ground etc

How horns work :

Battery voltage is supplied to the coil, and switch of the horn relay #36, in the underhood electrical center. The horn relay coil is energized when circuit 28 is grounded.
This may be done through the horn switch on the steering wheel, or through the Body Control Module when the horns are used as an alarm or a signal, for the Universal Theft-Deterrent System.
When the horn relay coil is energized, the normally open horn relay switch is drawn closed, and battery voltage is supplied to the horn feed circuit 29 through the horn fuse #11.

Common fault is the horn brush in steering wheel


Easy test with as below is that horn relay, push horn area of top of steering wheel and see
if ground than shows up as I pointed to
If no ground, then have to take airbag off to see horn switch or horn brush
Or maybe that wire from that to the relay