SOLVED - RPM drops when I switch on lights (low, high, fog) while driving - Toyota Corolla Altis Grande 2017 Pre-facelift

[tjbukhari1995]

AoA,
I have a 2017 Toyota Corolla Altis Grande (pre-facelift) and I’m facing an issue where the RPM drops when I switch on the headlights (low/high beam or fog lights) while driving. Interestingly enough, the RPM doesn’t drop when the AC is running at full speed without headlights and/or when idling.

I’ve already replaced LED bulbs with the original halogens, had a complete tuning done (fuel pump, injectors, throttle body, spark plugs cleaned/replaced, catalytic converter cleaned), and even installed a new car tracker. The alternator was tested by an electrician and confirmed to be working correctly (not undercharging or overcharging).

Despite this, my battery often ends up discharged, and I’ve gone through multiple weak batteries in less than a year. I also replaced the previous Phoenix 70L maintenance-free battery with a Daewoo DLS70, but the issue persists. I’d appreciate your advice.

Thanks

[smartdevil_striker]

WAS, seems like bad grounding... Check it's ground connections

[tjbukhari1995]

I had an electrician check the ground connection of the engine. The terminals and screws had a chalk build-up. They were cleaned. He also checked the ground connection of the light plugs, and they were okay as well.

[tjbukhari1995]

When the RPM drops, the accelerator pedal becomes unresponsive even if I floor it. But if I lift my foot a little and then press again, the RPM goes up; however, I can tell that the engine is under more load. But when I switch off the lights, the car accelerates normally.

[pwuser156532646969]

Have you installed any aftermarket brake/parking light in bumpers. The ECU controller might think you applied brakes whenever you turn on the lights.

[pwuser156532646969]

You have leakage current between parking light and brake light and whenever you turn on parking lights, the leakage current sends signal to ECU that brakes have been applied.

[tjbukhari1995]

I have actually. I replaced the reflectors in the rear bumper with LED lights. Those were installed recently as well.

[pwuser156532646969]

Remove the parking cable and keep just brake signal cable. If not resolved, completely remove the lights

[tjbukhari1995]

Bless you, @pwuser156532646969 brother! Removing those aftermarket bumper lights resolved the issue.