Rodcaine

Hi all,

TLDR: high beams and DRLs aren’t working, suspect headlight ECU is dead.

I recently bought a 2015 GS300h (L10 phase 2) in the UK. The car was in an accident in 2019 and sustained light front end damage. It seems that the damaged headlights were reused since a couple of the mounting tabs have been obviously repaired.

When I inspected the car I didn’t notice that the high beams wouldn’t work. D’oh! When trying to flash the high beams at night I noticed nothing would happen. I then played around with the headlights and noticed the following symptoms:
- When I turn on the car no lights in the headlight units will turn on (DLR, low beam, high beam). After 4-5 seconds the low beams turn on and the DLRs turn on dimly, no matter what position the light switch is in and whether it’s light or dark outside;
- When I turn the light switch to the side light or dipped beam position the dipped beams remain on, but the side light telltale will illuminate in the cluster. The tail lights will turn on too;
- When I pull the stalk to flash the high beams the blue high beam telltale illuminates. When I push the stalk away the ‘auto’ high beam telltale illuminates and this switches to the blue high beam telltale if I turn auto off;
- When I turn the dipped beams on via the stalk and then turn the fog lights on both front and rear fog lights illuminate as expected;
- If there is daylight and I leave the switch in AUTO the tail lights and interior lights turn off, as does the side light telltale, but the dipped beams and dim DRLs remain on.

After checking all the fuses that seemed relevant I was worried that the previous seller may have somehow wired the dipped beams to switched 12v to hide a problem with a control unit. I therefore pulled the fuses for the dipped beams and the headlights went out. I also checked all the wiring in the fuse box and around the headlights and it doesn’t seem to have been tampered with.

I got Techstream and scanned the car. This gave me the warning code U0182 with the diagnosis ‘cannot communicate with lighting control module’. This makes me think that the headlights are working in some sort of failure mode, and it would seem sensible for the car to activate the dipped beam if the LCM fails. I’m hoping this means that the LCM has simply failed and needs to be replaced.

I’ve been trying to work out where the lighting control module is located so I can pull it and inspect it. All of the information I’ve found so far relates to the AFS module, but I’m pretty sure my car doesn’t have AFS. It has the standard bi-LED headlamp units installed, as it did from the factory. Techstream indicates that AFS is not installed.

Does anybody know where the LCM is located on these cars, or if there are any fuses that may be protecting the LCM without being obvious?

peasodos

iTrader: (1)

Check the settings in the instrument cluster, you might have DRL turned off.

Below is a diagram from the FSM. Lighting control ECU is in the headlight. So it could be the headlights need to be replaced. to fix this. A connection internally could be damaged or loose. Or maybe your HID ballast is the problem.

Rodcaine

Thanks. There is no option to turn of DRLs in my computer settings. I’m not sure if this is because the headlight ECU is not communicating or maybe in the European market it’s not possible to disable the DRLs. *shrug*

From the reading I have been doing this evening it seems clear that the LED driver/ECU in the headlight is the most likely culprit. I’ll pull the bumper and headlight and test the connections, then replace the module if necessary. It’s odd because it must be getting power since it drives the low beams, so either it has partially failed or there’s a wiring problem for the CAN-BUS. Sounds like I’ll have lots of fun removing the bumper next weekend!

lexo98

iTrader: (2)

I was recently looking at the options on the Carista App and one of them is to disable the DRL

peasodos

iTrader: (1)

If it’s a dealer only option he can change it in techstream

Rodcaine

I don’t see it in the Techstream customisation options, but maybe that’s also because the module isn’t communicating. Can’t say I want to disable the DRLs anyway.

Goldkey954

Were you ever able to figure out the problem?

Robertcave

Here in the UK the DRLs cannot be turned of If this has had a bump i would suspect an earthing problem more than the CPU I do stand corrected i may add

Wataha88

hi. Can you describe what was the cause of your error? how did you fix it I have a similar problem on Lexus NX

Rodcaine

Sorry for the slow response. It took a while for this to get high enough on my priority list for me to pull the bumper off. When I got the bumper off I was really confused. All the wiring seems to be fine, headlights are intact, ECUs are clearly at least partially working since both low beams and DRLs work. Then I realised the problem!

The LH and RH headlight ECUs are different parts but the part numbers on my car are the same. It appears that a previous owner must have replaced the master LH ECU with a RH ECU. I have ordered the correct ECU and will update this thread to confirm if it works.

Rodcaine

Super slow update on my part. When I installed the replacement CPU the headlights worked correctly. It was an expensive repair but now the car is pretty much perfect!