Volvo XC90, 2007 Horn on, limp mode, many faults
 

Volvo XC90 D5 - 2007 Horn continually on, limp mode, many faults...

Horn is on continually if the fuse is in place. I have had a look at the CEM in place and there doesn't seem to be any obvious signs of water damage. Looking at the wiring diagram there seems to be a relay/switch in the CEM that I guess is no longer staying open.

Water may well have got into the yawl sensor under the seat by the amp about 6-8 months ago. There are signs of corrosion on the amp and some of the wiring in that area.

I put it on an icarsoft scanner and came up with an alarming number of errors:
500F State: None Air Condition, Faulty signal
7700 State: None Engine control module (ECM)
18B0 State: None Swirl actuator control, Offset fault
1517 State: None Turbo control, Pressure too high
9140 State: None Throttle module, Faulty signal
9190 State: None Throttle module, Faulty signal
0A31 State: None Control module communication, Signal missing from Engine Control Module (ECM)
0A31 State: None Control module communication, Signal missing from Engine Control Module (ECM)
0A31 State: None Control module communication, Signal missing from Engine Control Module (ECM)
0040 State: None Air quality sensor, Internal fault
0004 State: None Siren, Communication fault
000E State: None Steering wheel angle sensor, Internal fault (this was a bit iffy before)
1F00 State: None ECM, software, Faulty signal

Where do I start?

Any help appreciated!

Horn: start at the horn switch.

Test all parts of the Horn with VIDA, and monitor the switch with VIDA

Thanks for the reply - I'll start that tomorrow when I get some time.

You have a bunch of coms problems which are typical for a water damaged CEM

Remove and inspect the CEM. If any signs of water damage, then also inspect carefully the connectors on the loom which plug into the CEM.

If any sign of corrosion exist, you must clean and repair the corroded parts, and also fix the water leak causing the corrosion

I would start checking your swirl flap arm is attached and moving as this is the likely cause for quite a few of these associated codes.

So:

1) Angle sensor needs replacing - £35 - breakers costs
2) You need a new alarm Siren - £50 - £200 - breakers cost to new.
3) Your aircon probably needs a recharge - £80

Re the other codes - I wouldn't touch any of them until I understood the root cause as they are likely linked to 1 faulty part.

Hope this helps.

Update...

1) Horn fixed.
Turns out the CEM unit had some water damage. Took it out and discovered a bit of damp on it so sent it off to be tested / fixed. Replaced and cleared the big drain tube - loads of compost at the bottom of the drain tube at the 90deg angle. I also drilled a 10mm hole right in the corner into the engine compartment to help with the drainage (it's an old car!) and liberally applied sealant round the cover. Found out later that Volvo do a kit - Seal 30728861 & rubber grommet 30775689. Happy that the CEM can now be ruled out now.

2) Swirl flap arm is attached and moving OK (I think)

3) Performance is still rubbish on hills and has very slow acceleration.

Starting to get a feeling that due to the age of the car it's looking more like turbo issues or one of the fuel/air sensors?

When was the last time the fuel filter was changed?