SWM Horn Failure?

[SchwererVerlauf]

Hi, I’m trying to figure out why my horn and steering-wheel controls aren’t working. The horn is the only thing preventing the car from passing inspection.

The vehicle is a 2003 V70 with:

* Four-spoke steering wheel
* No DSTC
* Cruise-control and audio buttons

I replaced the stock AUM with an aftermarket head unit, so the audio controls aren’t relevant. I mainly need the horn working, but I’d rather not bypass the system by wiring a separate switch to the relay.

Current issues:

* Horn doesn’t work
* Cruise control doesn’t work

What I’ve tested so far:

* Replaced the clock spring no change.
* Had the airbag replaced under the recall no change.
* Activated the horn relay manually through VIDA. The horn works, so everything downstream of the CEM appears functional.
* Checked VIDA for input-value changes while pressing the horn and cruise-control buttons. None were detected.
* Tested continuity through the steering-wheel horn contact pads. They tested good.
* Checked voltage at CEM D12 while pressing the horn. It stays around 12 V, suggesting the CEM isn’t receiving the ground signal from the SWM/horn switch.
* Checked the SWM ground at A16. Measured 0–1 Ω, so the ground appears good.
* Checked continuity between SWM A15 and CEM D12. Measured 0–1 Ω. I also moved the harnesses during testing and found no intermittent connection.
* Back-probed SWM A15 to chassis ground while pressing the horn. A15 stays at 12 V, so the SWM doesn’t appear to be grounding the horn circuit.

The stalk controls including the turn signals, high beams and information display work normally. The power windows and hazard lights also work.

I’m out of ideas and would appreciate some guidance.

I’ve considered trying a donor SWM, but my understanding is that I need one from a 2002 or 2003 vehicle without DSTC. If I replace the complete stalk/lever assembly, it may also need to come from a V70 because of the rear-wiper controls.

From what I’ve read:

* The 2005+ SWM/lever hub and clock spring are different.
* The later clock spring requires a software download.
* The bus system and CEM may also have changed.
* Earlier and later model years use different firmware, bus speed or module revisions.

Is there anything else I should test before I can say the SWM’s PCB has failed?

[jonesg]

Try this, watch it on youtube.

[abscate]

The canbus changed in 2005 so you will need 2001-2004 parts. It does look like you have eliminated everything except that board, good diagnostic flow!

[SchwererVerlauf]

Try this, watch it on youtube.

I can get the horn to honk when I activate the relay with VIDA as I mentioned, I did post a wall of text so you might have missed it lol.

I pulled the relay out too, juuuust to be sure and I can hear it shut the contact with a magnet.
I've checked the fuse with a visual, and continuity test and it's fine, just to be safe again.

The canbus changed in 2005 so you will need 2001-2004 parts. It does look like you have eliminated everything except that board, good diagnostic flow!

Thanks, it's been a nightmare to figure this out, I have little electrical or mechanical know-how. It's been a good learning experience I suppose.

Is there anything I might want to consider or that I should be aware of when I'm looking for a used donor SWM from another car?

The XC70, V70, and S60 SWM should all just be drop ins, with no issue as long as its 01-04 correct? No programming needed with the CEM or VIN locks?
I'm unsure if the XC90 and S80 could be possible donors, if you happen to know about those two.