Skip the auto shop - Our mechanics make house calls

Q: My Toyota Avensis 2006 has had a dramatic Fall in MPG - pre and post-service

asked by on

I have a 2006 Toyota Avensis. It had a new clutch 6 months ago. Six weeks ago there was a sudden reduction in mpg from 43 to 37 for no apparent reason (no change in driving, conditions, route). Two weeks ago I had part of the gearbox replaced along with a wheel bearing - as well as a FULL service. The garage said that the mpg would rise after the service. In the week since I have picked it up the mpg has fallen further - to 33 mpg. I am driving no differently and using no different route to what I have over the last six years. It has always reliably done about 43 mpg. I have regularly tested this by filling up the tank, noting the mileage and noting the mileage again when I next filled up. Yesterday it had fallen to 33 mpg. The garage have now given me an additive to put in the tank when it is 1/4 full to clean it out - but surely that would not account for 12mpg difference in fuel consumption? Please help!

My car has 149000 miles.
My car has a manual transmission.

A: Hi there: There are multiple reasons why r...

Hi there:

There are multiple reasons why recent service might negatively impact fuel economy on newer vehicles. As the vehicle continues to operate, the ECU (engine control unit or module) continues to learn and make adjustments to ignition timing, fuel and air mixtures and fuel flow. When the service is completed, sometimes it takes more time for the ECU to update this information; and in some cases, if any error codes have been stored in the computer and have not been removed; it can impact fuel efficiency.

Another item to consider is your location. Fuel’s are changed prior to winter and summer seasons. Summer blended fuel tends to be a bit more refined; while winter blends are not as clean. As such, fuel economy can be reduced as much as 15% just on seasons.

The additives can sometimes quickly reduce fuel efficiency as they literally "burn" carbon deposits from fuel injectors. The best advice I can give is to keep running your Toyota for a while with normal fill ups (if possible from the same service station) and see if the MPG begins to slowly improve.

If not, contact a mobile mechanic, such as one from YourMechanic, who can come to your location to complete a diagnostic on your decreasing gas mileage. Best of luck.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: How long can I drive my car with the engine light on?

Hi there. It is no good to drive a vehicle with the engine light on. The engine light is on for a sensor has picked up something that is not functioning or operating correctly. Check the computer with a scanner...

Q: will it cause more damage if I continue to drive with a burnt out valve in the engine?

Hi there, thanks for writing in. Unfortunately, yes you can do more damage by continuing to drive with damaged valves. The misfire will cause damage to the catalytic converter, which is a critical emission device. Damaging the catalyst can cause...

Q: Something wrong with shifter cable and gears

I’ll assume you have a manual transmission. If you are having trouble shifting, there could be a problem with the cables. The clutch may cause this as well. If it is not fully disengaging, it will be very hard to...

Related articles

How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...