dropping fuel economy

Can you be more specific as to what a "judder" is? Not a term I have ever heard.

I take it that you are in Great Britian somewhere? Lower mpg can be the result of colder weather. Is this the first winter you have had the car? Snow tires?

 

I'm sure he means shudder, or shake. Hey If you can pnpoint this to your incident when the lights came on I would take it back to the dealer and have him check things again. In the states the 04's and early 05's have what's called here a "recall" where new software is downloaded into the computer or updated or whatever you wanna call it LOL. Sometimes the ICE shudder when it turns off at a traffic light or similar siutation, but I've never heard of the engine shuddering when it stats up. I'd take it back to the dealer.

 

you are in England and are going through cooler times... you might want to take a look at my blog entitled The Temperature is Dropping and So Is My Mileage!! it has to do with driving a Prius at city speeds and engine temps. i had a few runs that never got the ICE temps much above 160ºF although the running temps should probably be more in the line of around 190º

unfortunately, i didnt get my SCANVIEW in time to be able to gather any data during the summer months where the higher end of the temperature spectrum and its effects on economy could be observed

 

The "service light" came on. I would translate this to check engine light? Correct or incorrect? (Two English speaking cultures separated by a common language. ) No DTC (Diagnostic Trouble Codes)? That seems odd. I thought every time the Check Engine Light came on a DTC was generated. Are you sure there was no code or they did not tell you? The other is the temperature issue. Also in the colonies they change the gas from summer to winter and we take a 5 mpg or so hit. It happens around here at the end of September, when does it happen it the England. Also how far North are you. Here in Washington state we have a similar climate for similar reasons in you case the Gulf Stream in ours the Japanese current. We just got the first cold snap of the season with snow. We generally keep that stuff up in the mountains where you can visit it when you want. With temps in the high 30's F (you remember Fahrenheit?) I took another 2-5 mpg hit. Details Details Details. Give the bright people around here info and you will get some. We even have a few Prius Techs floating around. A number of us have service manuals to use as a reference.

 

i think it was the oil change light he was referring to. you might want to check your tire pressures and oil level fills for other possible causes