My G37s has a weird issue where in the daytime i press the brakes my city light turn on and my interior lights turn on and my screen goes dim but it still accelerates like normal when i drive. its a whole different story at night, i turn the headlights on and the car at full throttle gives maybe about 15-25% of the actual power and basically feels like its in limp mode. its a super weird issue and i need to get it fixed soon as when i need to overtake at night i have to turn my headlights off so i can get enough acceleration to make a move, and the brake lights are always on whenever the headlights are on, any ideas on what the issue could be, please do help me out

 

Welcome, but no way to advise you further without more details. First when did this electrical problem first crop up? Have you checked for codes? Any mods to your G that might be connected to the headlights? How many miles are on this G and did the previous owner mention anything on it?

 

thank you dkmura, this started around about 5-6 months ago a couple weeks after i got the car, there was this one instance where i had to slam on the brakes to avoid an accident but im not sure if the problem was there before or after that, had the car computer checked by 2 mechanics and there are 0 codes on the car and there arent any mods to the headlights yet so im not really sure whats happening, the previous owner did not have this issue.

 

A shot in the dark, but check the switches at your brake pedal. Being that you had to "slam" on the brakes it's possible the switches got damaged/ misaligned. These cars exhibit odd behaviours when those switches are not right.

Also, the obvious, any water in the passenger-side cabin?

 

yeah i was thinking it might be something to do with the brake switch but its pretty odd how only when the headlights are on it goes into the limp mode thingy, it does that weird dim screen and lights when i press the brakes in the day time to aswell, would you know if theres a separate switch for the cruise control and the brake switch or are they both the same?

when i turn the headlights on it basically has the brake lights and the third light on the spoiler turned on at all times, do you think the car feels as though the brakes are being held so it doesnt let me accelerate as im supposed to?

 

and no, no water in the passenger side cabin, i live in dubai so theres barely ever any water issues here

oh and also the cruise control does not engage when the headlights are turned, probably because the car thinks im pressing on the brakes.

 

These are all separate and isolated systems - Brakes - headlamps - ECU - TCM

For example, The brake llights are a basic power/wire/switch arrangement. The only way to get the brake lights to come on is to operate the brake pedal switch. Literally no connection between the brake lights and headlights.
The headlights use the Canbus and the IPDM/ER for control and the ECU and TCM are tied only to engine / transmission functions and are he only things that could put you in limp mode.
There is also a tie in to the the ABS module through the a second set of contacts in the brake pedal switch. still not connected to the other systems though.

The only thing i can think of is a wire harnes that carries all the wires for the problem systems is damaged. Meaning some random group of wires are shorted and when you switch on the headlights it sends random signals everywhere.

This is a good one, keep us updated once you solve it!

 

alright boys finally got the time to take the car over to an mechanic for this issue that me and my friends have started calling “batman mode” and turns out you guys were right one of the circuit boards shorted and messed with the brakes and headlights of the car, it has now been resolved. thank you guys