Daylight sensor troubleshooting

[poolski]

I recently installed a new head unit in my 2009 Jazz. To do that, I disconnected the battery to make sure I didn't fry anything important while arsing about with the electronics.

Once I reconnected the battery, I found that about 30 seconds after starting the engine, the headlights would come on when the light selector was set to AUTO. This would be fine if it wasn't broad daylight.

I'm wondering whether I've blown a fuse somewhere or there's some weird electrical imbalance or short within the head unit's wiring loom.

The fact that the lights don't come on IMMEDIATELY suggests that there's a voltage reading that climbs/falls steadily somewhere until it trips the "IT IS NOW DARK" threshold.

Does anyone have any suggestions?

[GBH]

Would also like to know about this.

On occasion I have started a journey early morning with the lights on "auto" and working fine but about half an hour later, in bright sunlight, they remain on.  Conversely, they sometimes fail to come back on when the ambient light drops.

[poolski]

Update:

It seems like it's settling down again. I wonder whether the MICU (Multiplex Integrated Control Unit) needs to calibrate the sensor readings, which takes some amount of either time or engine restarts. From what I can tell, the MICU handles stuff like automatic lights, wipers, etc.

It's not outside the realms of possibility to think that disconnecting the battery purges the "daylight" data from the MICU. If I were to make an educated guess, I'd say that the ECU has permanent storage - it has to, for things like the engine timings and odometer - which isn't purged by disconnecting the battery.

I wonder if the MICU's onboard storage is dependent on having power...

In any case, my light sensor seems to get it right more often than not now. It's still a bit too "keen" to turn the headlights on - for example when I drive under a tree for about a second - but it's getting better...

[GBH]

Update:

It seems like it's settling down again. I wonder whether the MICU (Multiplex Integrated Control Unit) needs to calibrate the sensor readings, which takes some amount of either time or engine restarts. From what I can tell, the MICU handles stuff like automatic lights, wipers, etc.

It's not outside the realms of possibility to think that disconnecting the battery purges the "daylight" data from the MICU. If I were to make an educated guess, I'd say that the ECU has permanent storage - it has to, for things like the engine timings and odometer - which isn't purged by disconnecting the battery.

I wonder if the MICU's onboard storage is dependent on having power...

In any case, my light sensor seems to get it right more often than not now. It's still a bit too "keen" to turn the headlights on - for example when I drive under a tree for about a second - but it's getting better...

My headlights also turn on when driving under a shady tree, and I can live with that but it also goes the other way when, for example, I start my journey at dawn but the lights stay on when the sun comes out.  It is as if I have not switched the lights to "auto" when I know I have.

I am beginning to wonder if this requires specialist dealer only software for calibration (much like VW cars can be interrogated with any OBDII device but only down to a basic level and require VCDS / VAG-COM software and cable to make sdjustments).

[poolski]

Update:

It seems like it's settling down again. I wonder whether the MICU (Multiplex Integrated Control Unit) needs to calibrate the sensor readings, which takes some amount of either time or engine restarts. From what I can tell, the MICU handles stuff like automatic lights, wipers, etc.

It's not outside the realms of possibility to think that disconnecting the battery purges the "daylight" data from the MICU. If I were to make an educated guess, I'd say that the ECU has permanent storage - it has to, for things like the engine timings and odometer - which isn't purged by disconnecting the battery.

I wonder if the MICU's onboard storage is dependent on having power...

In any case, my light sensor seems to get it right more often than not now. It's still a bit too "keen" to turn the headlights on - for example when I drive under a tree for about a second - but it's getting better...

My headlights also turn on when driving under a shady tree, and I can live with that but it also goes the other way when, for example, I start my journey at dawn but the lights stay on when the sun comes out.  It is as if I have not switched the lights to "auto" when I know I have.

I am beginning to wonder if this requires specialist dealer only software for calibration (much like VW cars can be interrogated with any OBDII device but only down to a basic level and require VCDS / VAG-COM software and cable to make sdjustments).

Stuff like this is why I'm all for the Right To Repair stuff being enshrined in law, compelling manufacturers to make their diagnostic tools available for purchase by the general public. Nobody's suggesting they give them away for free, but having to register as an authorised service outfit and paying thousands to get at the car's innards is absurd.

I'd be more than happy to plug my laptop in and have a poke around - my car's not under warranty, so there's nothing to void.