Petrol Engine Keeps Running

[Ponder]

I am experiencing a problem with my Prius that the dealer hasn't been able to fix. The symptoms are that once the engine has warmed up enough, the petrol enging starts and stops depending on the demand. After a while, when it has fully reached optimum operating temprature, it starts to behave quite differently. The petrol engine runs continuausly, regardless of the demand. If I am coasting down hill for more than a few minutes it does eventually stop, but starts running continuously again as soon as it is next required even briefly. Only once I have been completely stationary for at least 6 seconds does this behavious stop, and will not return for the duration of the journy, regardless of how long the journey is.

Has anyone else experienced this? and any idea how to fix it.

[timberwolf]

If your car is not displaying any warning indications and if the Toyota mechanic had no diagnostic codes to read, then your car is fine, so try not to worry too much about there being something wrong.

What you could be seeing, although I'm not sure from your post is that your Prius could be staying in Stage 3a (see the link below) due to the route, traffic conditions, driving style, etc that you usually drive.

http://www.techno-fandom.org/~hobbit/cars/five-stages.txt

[Chris Dance]

Thanks timberwolf: That is a good article and explains the engine operation etc clearly.

Ponder: From reading the article I think timberwolf is correct; there is nothing wrong with your Prius.

[gniie]

Just a little observation.

The first generation Prius( NHW11) had been set up to start the air con automaticaly on full power when the vent system was set on de-fogging(at least on my jap import). That would keep the engine running almost continuos to supply power for the air con system. Maybe the new model(NHW20) has the same setting and you are keeping the vent system on de-fogging setting all the time .....?

[timberwolf]

Yep, if you turn the front window demister on the engine will run a lot more often - I can't recall if it's nearly continuous though I didn't do much driving when it was cold.

With the Gen 3 coming along we won't be able to call the Gen 2 a new model for much longer

[GreenJuice]

I agree. It appears that almost any significant demand for energy to the cabin (heating, cooling, demisting, etc.) in the soon-to-be-old-model Gen 2 will cause the engine to run, until you have completed the warmup procedure and entered Stage 4. To do that, your engine coolant temperature must be above 70C and you must come to a complete stop for 5 - 10 seconds (although you can cheat a little by creeping at under 6 mph!).

I used to think this 'engine running' behaviour was unpredictable or chaotic until I installed a ScanGauge II to monitor the engine temperature (amongst other things). Without SGII, you can still be fairly sure you have entered Stage 4 - it is as soon as you notice that peculiar 'engine-running-for-several-seconds-whilst-stopped,-before-shutting-down-with-a-judder' behaviour. Compared to other cars, I found that the Prius took much longer to reach its ideal operating temperature (in some of my journeys - up to 30 minutes). By watching the engine temperatures, I now realise its actually a sign of how little fuel the Prius is burning!