Help! Prius doesn't shut off ICE - Fuel Economy, Hypermiling, EcoModding News and Forum

Antuanos · 06-11-2010, 01:12 PM

Hi!

I've noticed lately that my Prius (2008) sometimes decides to keep the ICE running even though the engine is warm and the gas pedal is not depressed. I don't know why it does that. I have to press the EV button to be able to glide. Quite annoying... I bought the Prius just to get rid of the ignition jerking.

Regards
Anton from Sweden

Daox · 06-11-2010, 01:38 PM

Sometimes the Prius is a bit quirky. Normally, its because you haven't entered S4 mode yet. You have to stop for a few seconds so it can do its check before it'll go into S4 and have the engine off on demand.

Antuanos · 06-11-2010, 02:01 PM

Hmm, but why would the prius suddenly go from s4 to s3 whilst driving? Is that normal?

Daox · 06-11-2010, 02:26 PM

The prius will drop from S4 to S3 if the coolant temp drops low enough. Or perhaps you weren't in S4 to begin with. AFAIK (and I could be wrong since you have a 2010), but you need to stop for a good 3 seconds with the engine running to get into S4. If you haven't done that, you aren't in S4 and may or may not be able to stop the engine on demand.

Antuanos · 06-11-2010, 02:37 PM

That makes sense. I guess the only way to go around that is to block the air intake?

Daox · 06-11-2010, 02:47 PM

In winter its very common for my 04 to drop the coolant temp that far (below ~158F I think). In summer its not real common. I'd be more inclined to think you never actually entered S4.

Antuanos · 06-11-2010, 02:58 PM

Daox: The system works as normal when the engine is semi-cold, so the problem shouldn't appear when I've been driving around w/o problems for about 10-15 minutes.

There's something fishy going on. The problem is occuring more and more often.

Does anyone know what could be the problem?

2009Prius · 06-15-2010, 03:56 PM

Assuming this is abnormal as you described (entered S4 successfully but later apparently got out of S4 without the engine or the cat getting cool), I would start by checking the 12V battery and the MAF sensor. Good luck!

Matt Herring · 06-15-2010, 04:35 PM

In my 2010 I sometimes get bumped into ICE for various reasons. I'll be at 180 F and 10 miles into my drive and can't get the ICE to shut down. Usually for me the culprit is low SOC from heavier than normal use of EV under 45 mph. Once the SOC goes from 2 back up to 3 bars I can get back into EV.

2009Prius · 05-21-2011, 12:07 AM

Well it has happened to me in a few drives and it happened for many times during my drive home today. The weather was nice, temperature about 70F. The SOC wasn't low. The engine was warmed up. The car had gone through the S4 "dance". It would drop out of S4 (engine not shut down during glide or regen). Then it came back to S4. Then later it would drop out again, and then came back to S4 again. This happened well into the drive when everything should have all warmed up. In the past I had assumed the cat temps may not be high enough. But today I watched them and noticed that there were occasions when the car dropped out of S4 at cat temps higher than those at which the car came back to S4 later. Any idea why the car would drop out of S4 well into a long drive?