What if engine check light turns on and turn off again?

Hi,

I have a VW polo 2002 1.4 benzene. I went on a long route 600kms drive in a day with speed of around 100-120km per hour. I was driving in midway my steering became hard, steering light turned on. I stopped the car, opened bonut, there was some fumes coming from battery. I stopped for few minutes. Turned off the car and turned on again, all the lights were off in dashboard and steering was working fine. I drove at very slow speed to backhome somehow. Now i started next day, the start of car was not normal. The starting sound was not powerful, seemed like battery was not giving power, but somehow it started. I checked again, it started but with not normal start. I felt battery power is low. Now all the lights on dashboard are off and steering is also working fine. What could be the problem?

Typically if a CEL turns on and off it means the problem is no longer present however pulling the battery leads means you cleared all memory in your ECU. Batteries do not smoke instead they create hydrogen gas (very flammable) from what it sounds like either you battery has an internal short sapping all the voltage produced by your alternator or inversely your alternator is producing too much voltage causing your battery to boil over. Is it a completely sealed battery? You could try to pull the caps on each cell and check the electrolyte and recharge or better yet start by replacing the battery and see if the problem persists. Also if you have a multimeter check what voltage your alternator is putting out by putting the leads to the terminals on the battery while the car is running. Too much or too little voltage will cause some very funky issues youll be looking at about 13v on the low end and about 14.3-14.7 on the high end of the spectrum. If youre running at 15+ or below 13 volts i would suspect theres an issue with the voltage regulator. Alternators almost never lose their ability to create a charge but instead an issue occurs with the voltage regulator unsure if your vehicle has an internal regulator or an ECU controlled regulator. Hope that helps and you figure out your issue bud!

You may use "VCDS" for a read out, to find out, whats wrong.

You may can even delete it via "VCDS"

Sometimes loose, cracked, or faulty gas cap can cause fuel to evaporate, thus cuing your check engine light.