Setting position for auto levelling headlights - nightmare

[TUS373]

My old Lexus RX400h went if for MOT last February and when I collected it, they said that they had had to fix the automatic headlight leveling. They are xenon lights. There is a tiny adjustable bar on the rear suspension, that attaches to a potentiometer, that talks to the headlights, so that when a heavier load compresses the suspension, it compensates dropping the beam slightly.

It was all working OK, so I was surprised when they told me it was not working. I think what happened is that they touched the adjustable bar, it was already corroded, and it broke. They kind of bodged it back together for the MOT. Soon after, there was a warning light in the dash indicating an error with the system.

I bought a replacement bar. It is threaded at both ends, so can be spannered to make it long or shorter. It was fitted, but the warning light would occasionally come on.

So...I bought a new potentiometer in case the electrical part was also not working. They fitted it, and the warning light went off on the dash and stayed off. Fixed!

No. Now my headlights were pointing too high, dazzling on coming traffic. Back to the garage.

Their solution - adjust the headlights. They did this a month ago. I do not think they used the MOT type machine, but played with the adjustment screws on the units. But still....too high. I can tell.

Had car in yesterday for a pre MOT check and they told me that the sensor is faulty and that the adjusment screws on the lights are faulty. Well, they were OK a month ago - they never said anything.

So, back to square one. I have bought a complete new, after market sensor/bar combination, just in case this is needed to get through MOT. However, I am thinking that everying needs 'tuning' back together now. So say, set headlights in the middle of the up-down range, then install sensor and bar, make sure that sensor is in right position to start with, adjust bar length to correct length to influence the headlights.

How shoudl they actually go about re-setting everything? It has been going on as a problem now for 12 months with something always out and the beams set wrong. I am a responsible driver and need this fixing so as not to dazzle other road users, MOT or not.

Thanks!