I recently bought a used 2003 Opel(Vauxhall) Astra G 1.4. I drove around 2000km's in the last few months (city and highway mixed), and I used about 200 litres of gasoline, which means a 10l/100km consumption. This seems a little bit too much, and it might be because I'm really a new to driving. According to other sites, consumption should be much lower (around 6-8l/100km).

A friend, who also has the same car told me, that it probably consumes more, because I have not reset the car when I bought, and it is "not used" to my driving style. He told me to take the battery out, and put it back 20 minutes later, then drive around in low traffic for 20 minutes. Would this really cause better settings in fuel consumption? I don't know too much about cars, and I don't understand how this would work.

Thanks for every answer in advance!

UPDATE: Yesterday I did the ECU restart by taking out the battery, I can't say too much about consumption yet, but the first thing I noticed was that acceleration in 1st gear was smoother than before. So it definitely had some effect. I'll update again when I have enough data about fuel.

UPDATE #2: In the last days I used ~25-26 litres at 270km's, so it didn't really change (it was the same ratio of city/highway than before)

4 Answers 4


Yes, a reset could work, if the problem is that the ECU is used to the previous driver's driving style and his style was vastly different to your's. But it could also just be the way you drive. Do you drive more like Morgan Freeman or Vin Diesel? These cars are quite heavy on the juice in city driving. With mine, I get about 7.5l/100km on the highway going 110km/h(70mph), but in town it goes up to 13l/100km. It really does depend on how much time you spend going slow in lower gears versus going fast in top gear.

Also, the 1.4 Astra has a very short ratio gearbox, which isn't good for consumption either. You would probably find that the 1.6 with its longer gears would be better with consumption in the real world.

  • The previous owner was a company, where it was used by several salespersons who didn't had a private company car, and people whose company car was under repair. So it is indeed possible that the car is used to some different driving style. One guy who used the car at the company told us that it was about 6-7l/100km for him overally, but he used it mostly on highway. What does 'short ratio gearbox' mean exactly? If I understand it correctly, it means that I should change to higher gear on lower RPM than usual to get better consumption?
    – adam434
    Aug 14, 2014 at 11:54
  • Your consumption figures are actually spot-on for the car. A short ratio gearbox is one where the car revs high and you don't get lots of top end speed in each gear. Also, the difference in RPM between two gears is less than usual. Aug 14, 2014 at 12:15
  • Have a look at the consumption figures on this page um.co.za/specifications/… granted, it's a 1.6, but the consumption should be very similar. Aug 14, 2014 at 12:16

I don't see it helping any. The long term fuel trims on modern cars will adapt to conditions within 15 minutes of driving, and even those only have a minor impact. The short term fuel trims that have the most impact adapt pretty much instantly (hence the "short term").

All that said, resetting the ECU is easy, so feel free to go for it and let us know what happens. :-)

If I reset the ECU on my OBD-I car, nothing changes at all. If I reset it on my OBD-II car, the car runs bad for the first 15 minutes, then starts running normally again. I get slightly better gas mileage on that tank because the car was running too lean until it relearned the fuel trims...


I don't think a battery reset can improve your fuel economy. But do check whether the battery is working properly.

Read this link here to get an idea of how to improve your fuel economy.

  • It's possible. I have the 2.0 Turbo version of the OP's car and each time I have to disconnect the battery, I get about 30 to 50 extra kilometers out of a tank of petrol. Aug 14, 2014 at 10:53
  • Oh really? Am not aware of that. Could you please explain more, if you don't mind.
    – Rohith
    Aug 14, 2014 at 10:55
  • 1
    The Opel's ECU (developed by Bosch) "learns" your driving style, i.e. your habits with the throttle at certain RPMs. It then adjusts the timing advance and (I think also) fuel injectors to offer you the best overall performance. "Performance" meaning either throttle response, acceleration, fuel economy depending on how you behave. If you drive fast a lot, it "learns" to favour throttle response and power output over emissions targets and economy. Aug 14, 2014 at 11:05
  • So by battery reset, ECU memory is cleared. Right? Got it.
    – Rohith
    Aug 14, 2014 at 11:07
  • 1
    Try it. Mind you, when I say "learn", it really just means it adapts slightly. It's not intelligent, so don't expect miracles. Aug 14, 2014 at 11:09

Disconnecting the battery on your car will do nothing to improve fuel consumption. If you disconnect the battery to lose any memories the ECU will revert to EOL (End Of *production*Line) programmes. Driving the vehicle will then reset fuel trims to minimise engine emissions and consumption using the oxygen sensors, and anti-knock sensor for maximum ignition advance. A check on the oxygen sensor switching and voltages will tell you if it aged or not. Renewing an aged sensor will improve MPG, but the sensors can last from around 50,000 miles to several times that mileage. Switching speeds and voltages are the key. If the knock sensor is out then you will have pinking. The accelerator pedal position sensor speed of application will affect injector opening times, longer injection opening times-more fuel used. The differance between the fuel consumption between differant drivers is dependant on their sensitivity to their driving style. Gentle acceleration, anticipation for gentle braking, good maintenance of the vehicle, even down to the correct oil in the engine as modern low-viscosity oils lend themselves to MPG, tyre pressures correct, any unnecessary 'luggage' in the boot removed and anything like roof-boxes removed so that the tractive effort of the vehicle is at a minimum all go towards an optimum MPG.

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