Quite a while ago I posted about a strange issue with the OEM stereo in my Lexus IS250. It would randomly turn off, or turn on all by itself while driving. Sometimes it would do it once then be fine for several weeks, sometimes it would do it multiple times on a 15 minute journey. Sometimes it wouldn't do it at all for weeks.
Eventually - by the time honoured system of pressing random buttons and seeing what happens - I was able to pin it down to an issue with the power/volume knob on the fascia. It seemed that by adjusting the volume with the knob, rather than the steering wheel controls, it would trigger the turning off/on behaviour. If the volume was set just right then it seemed that the random switching off and on wouldn't happen (much), leading me to suspect that the knob had somehow been damaged. It was quite strange because its not situated in harms way, so I'm not quite sure how the damage occurred but it did seem to be that.
By this point I had purchased a 2nd hand head unit and it had sat on my bookshelf for several weeks. I had a day off from work and decided that it was a good day to attack the job. The plan was to swap the entire unit over for my new one in the hope of fixing the issue.
Removal was a fiddly job involving removal of various bits of centre console trim, using a screwdriver to carefully unclip the centre console vents, then unbolt the entire stereo and satnav unit without punching a hole in the screen with the gear selector! With this carefully done, I was able to undo the wiring harnesses from the back of the stereo/nav unit and lift the whole thing out of the car and take it indoors to tinker with.
The next step was separating the stereo/cd player from the nav unit, this required unbolting the brackets from the sides of the unit then sliding the stereo off the bottom of the nav unit. So far so good. Next, I refitted my replacement unit, bolted the brackets on then took it back out to the car to refit the wiring harnesses, and this is where I hit the first snag
The wiring harness on the back of the stereo was totally different. OK, back to the drawing board. Very close inspection revealed that the old stereo was a P3833 model, and the replacement was a P3831. It looked identical, but the harness for connecting the stereo to the rest of the ICE, and steering wheel controls was very much not the same.
The rear of the 'old' head unit looked like this:
While the new unit looked like this:
Not ideal. So back to the drawing board. I had a sit sown and a think then had a brainwave. If it was just the volume knob that was playing up, then possibly I could swap over the fascias, so I kept the majority of the old stereo mechanism, but changed just the fascia plate.
The fascia plate unscrewed fairly easily - 2 screws each side
With these undone, I used a blade screwdriver to lift the tabs holding the fascia to the mechanism and it popped off
The two fascias were identical, and connected to the mechanism with the same oblong connector block
I carefully mounted the new fascia to the old mechanism, refitted the screws, then bolted the stereo the the sat nav with the brackets and took it all out the the car. I've had situations like this before where all the bits physically attach to one another, but refuse to work how I expect so my confidence was low at this point!
I gently lifted the (fairly heavy) stereo and sat nav unit back into the dashboard, and connected all of the harnesses up. At this point the stereo mechanism was the original one, so the harnesses all connected fine - only the fascia panel was different. I left the rest of the trim and vents unplugged in case I needed to take it all to pieces again, but turned the ignition on and was delighted to find that it all worked as expected! The new fascia buttons all worked, I could change the volume and power the stereo on and off with the knob on the stereo unit. So obstacle 1 overcome.
Next I reassembled the centre console and dashboard and bolted the stereo and nav head unit back in properly then went for a drive to make sure it would stay working.
I'm pleased to say that 3 weeks on, its still behaving perfectly. There must have been an issue with either the power/volume knob or the PCB in the fascia causing it to intermittently send the 'power' signal to the cars ECU and either cutting the power, or switching on the power as though the power button had been pressed, even when it hadn't.
The only issue now is that the stereo model number on the front of the fascia is now wrong! So for future owners, its a P3833 mechanism with a P3831 fascia!
Total cost of repair was just £23 for the second hand stereo and an hour of my time taking it to bits and rebuilding it. Far far cheaper than replacing the whole unit with a used one (~£350) or replacing it with a new Teyes head unit (~£550) which were the only other two options. I might even be able to recoup my costs selling the P3831 mech and damaged fascia to someone (with issues disclosed!) who needs a mechanism but has a known-good fascia.
