No Heat; Stuck in Recirc Mode; Occasional Master Warning Light

This just started today. It's still cold up here in New England, and I noticed that the Prius was blowing cold air with the air conditionioning system set on auto and 68 deg. The recirculation indicator was illuminated, but neither the climate page on the MFD or the steering wheel button could turn it off. I tried "rebooting" the Prius and it did no good.

On the way home tonight, the Master Warning Indicator illuminated for five seconds or so, and then went out.

No heat, air recirc always on, occassional Master Warning Indicator: Any ideas? Thanks!

Karl
2004 60K miles

 

Thanks, Jay. It didn't throw any codes.

This is a little frustrating. In a normal car, I'd sort of know where to start. Or at least I'd know who the usual suspects were if the heater stopped. In the computerized marvel, I'm clueless. I am also wondering why the master warning symbol briefly illuminated while driving. In the six years I've been driving this Prius, that has never happened.

It's locked in recirculation mode, which I suspect is just a symptom of the underlying problem.

If anyone has any other ideas, I'd love to hear them. Otherwise, it's probably off to the dealer.

 

The air filter was the first thing I checked. Not as a result of a brilliant line of reasoning, just because I couldn't think of anything else to look at.

"Recirculation on" might be a red herring. I wonder if the heating system works similar to the A/C--if the differential between desired temperature and actual temperature is over a certain threshold, the system shifts to recirc? I just never recall seeing it when the system was calling for heat.

I knew that if the check engine light was illuminated, you would find stored DTCs. I didn't realize that you'd find a DTC with the red triangle of doom, too. I'll report back when I finally figure out the problem.

 

Epilogue:

It was simply a bad water pump. The red triangle master which had been very intermittent, finally stayed illuminated. Eventually, a water temperature icon appeared on the MFD.

The coolant reservoir always showed full so this threw me off track.

If anyone is getting near the end of their 5 year powertrain warranty, I would check the waterpump for leakage. It's an expensive 3 hour $450 repair. I watched the technician perform the swap, and it didn't look like an easy do-it-yourselfer. Like everything Prius, it's not your grandaddy's waterpump.