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Prius at altitude

We bought a 2002 Prius in Ohio in April of 2002. Drove it to Sacramento in September of 2003. It has been in the Sacramento area since, with occasional trips to the bay area and Tahoe. We have put 95,000 miles on it and have had no problems with it outside of normal maintenance. This past May we drove it to Tahoe with the intention of staying three days. The morning of the second day the gas engine would not start, there were three different trouble codes listed on the dashboard indicator. The car would run OK on battery. I called the local Toyota dealer and talked with their Prius expert. He said it is probably the altitude compensator. He suggested towing it to the shop (driving it to the shop would probably deplete the battery) and they would check it out.

The car would not start for them either. They hooked up the diagnostic checker and according to him did not get any abnormal codes. They reset the on board computer and the engine started OK with no more codes showing on the dashboard. We drove the car around Tahoe all that day and had no more problems. But after parking the car overnight, again it would not start and the same trouble codes showed on the dashboard. Again I had it towed to the dealer, they again cleared the codes with their diagnostic checker and everything worked fine. They could give me no explanation of why it happened the second time or for that matter why it happened the first time. I filled the car with gas and drove it home.

We have driven the car around the valley since and made one more trip to Tahoe (a day trip only) and have had no more problems. The local Toyota dealer has no idea what went wrong and says he can?t do anything more until the car acts up again. I have not been able to find out if the altitude compensator will give a separate code or whether that was just a WAG. I also wonder if the gas in Tahoe (altitude 5000 feet) is different than gas purchased at sea level. Do you have any ideas?

I don’t know exactly what the altitude compensator is; but most likely referring to the mass air flow sensor (MAFS) located under the engine air filter. It might be dirty, in which case it can be cleaned carefully or replaced.

A common problem in 2001-2002 Prius is related to the engine control module (ECM; one of the on board computers). It the gas engine does not start promptly enough, trouble codes P3191 or P3101 may be set. Just for fun I’ll try to attach TSB EG011-03 which should be good reading for you.

If my hunch is correct, you will be wanting the 89661?47054 ECM. No smaller number in the last two digits will do. I got my “54” under warranty but you are probably past that. Ask Toyota how much it costs. After you recover from hearing the price, see if one of the salvage vehicle dismantlers (such as LKQ online) has a “54” for sale. Even a DIY could exchange them.

Please post again so the accuracy of my hunch can be tested. Good luck.