P0117 - how to diagnose?

Yesterday after around 10 miles of in-town driving, I got on the freeway at the beginning of a long steep uphill, and less than a minute after reaching 70mph the red high temp light came on the dash, followed by the CEL less than 30 seconds later. I was already pulling over when the CEL came on, and the red high temp light went off before I was fully stopped - it had been on for only 30-45 seconds.

There was lots of red coolant around the reservoir area and on the passenger tire area and some drips on the pavement, and the reservoir was low but not empty. No steam or smoke, and at first I thought a coolant hose had popped off, but looking carefully at the spray pattern I realized it had shot out the reservoir overflow. I had a jug of coolant in the car and refilled the reservoir to the F line, there was only a tiny bit of pressure released when I opened the cap. I drove the wrong way back down the shoulder into town in EV mode, the engine ran once for less than a minute before I got home. There were lots of small red drops around the undercarriage on the passenger side when I parked it in our garage with clean concrete, but today there was no sign of coolant on the garage floor.

Today I drove it 5 minutes to the local NAPA to get the code read, the guy just plugged it in and said I should take a picture of the code reader, no comprehensive printout like OReilly gives (but they're 20 miles away). I asked if there was more than one code and he said no, and I came back home to figure it out. Here's the photo of the code reader:


Looks to me like there were two codes! I don't have any experience using a code reader, is that what it looks like to you? If there's a second code, I'll have to go back to get it also. The coolant in the reservoir hasn't dropped since I filled it on the shoulder.

It's a 2013 Prius v with 138K. Head gasket was replaced (done by Gasket Masters in Manteca CA) at 131K (thread here), after having done (myself) spark plugs, full EGR system and intake cleaning, replaced PCV, installed OCC, etc at around 126K. Since the HG replacement it's performed normally, I've monitored the coolant level and it's never moved until the cap let some spray out yesterday.

Reading through a dozen or more threads here, it looks like the P0117 code by itself isn't much of a diagnostic, but if it's combined with P148F it indicates a failing water pump. Based on feedback from my previous thread, I had put "replace Prius water pump and thermostat" on my to-do list but didn't feel like it was a priority. But I'm not driving this car (except to get the code read) until I have a solid diagnosis, so now it's top priority!

Should I do anything other than go back to get both codes read (assuming there's a second one) ?

 

Thanks, just wanted to double check before going back to get both codes this time.

Yeah, given the brief red temp light on the dash and over-pressurized coolant pushed out of the reservoir, it seems very unlikely to be a simple wiring issue on that sensor, and the most likely diagnosis is a failing water pump, like the way several threads have photos of a cracked beige plastic part or indications of the impeller not turning freely. That would perfectly explain my experience, and fortunately the over-temp condition seemed to be very brief.

The only nearby place that I know will read codes is closed until Monday and I'm not inclined to drive it further, we have a second car and can wait until then. I'll post again when I find out whatever that code is, hopefully it'll be something that gives a conclusive diagnosis so I can avoid operating a parts cannon!

 

Right, all signs point to a brief overheat, there's no other plausible explanation for the code.

What device do you have that monitors coolant temp on the dash? I assume it's something plugged in the OBDII port? I've always wanted more obvious metrics while driving but also hoped things are designed and engineered well enough that's not necessary - unfortunately I'm finding out otherwise.

See below for an update and more questions!

 

I spent yesterday fixing my washing machine, when it rains it pours! Today I went back to the local NAPA, but when I turned the car on, the CEL was off. Dangit!!! Of course they said their code reader won't report anything unless the CEL is on. So whatever that second code was (that they should have noticed the first time) may be forever lost. I've come to appreciate NAPA in general, but have had bad experiences with this particular place over the years.

So now I'm in a weird limbo state, knowing that it briefly overheated but without the second code, it's hard to conclusively diagnose the water pump itself. I'm inclined to just replace the water pump and thermostat regardless - it's the one further point of action that I'd planned to do sometime after I had the head gasket done. It seems like people tend to use the OEM part - is there any reason not to? I'll do the work myself, and don't mind spending more on something critical like this if it's more likely to last.

Also, maybe this should be a different thread, and I'm about to go down the rabbit hole searching the forums here, but what are the options for getting a code reader? I know there are lots of Chinese ones on Amazon that are like the ones at parts stores, and also little bluetooth devices with a phone app that can do real-time monitoring of various things, which seems worthwhile if it's done well. Any tips?

 

Thanks for the suggestions! I went down the rabbit hole a bit and, as expected, the topic of OBD readers is somewhat complex with several tradeoffs. That deserves its own thread, which I may post tomorrow if I can't come to a conclusion on my own.

Meanwhile, is there any way to retrieve whatever was the second code that the incompetent NAPA employee told me wasn't there when it clearly was? I'm inclined to load the parts cannon with a water pump and thermostat, but would love to just get that second code for confirmation first. Is there any way to read historical codes?

 

Hmm, I read through those but didn't see anything about reading historical codes. Both deal with the "blink codes" from the ABS/TCS system, which I had to figure out a year ago when my brake booster started to fail. I made a video of them so I could pause it and record them, but that's because I don't have a code reader and it was easier than taking it somewhere.

In this case I want to read whatever the last code that the ECU set last week, but then self-cleared after it sat over the weekend. Is that possible, and if so how?

 

Wow, that's exactly the kind of thread I was hoping to find! It didn't come up in my search, thanks for the link. I actually read the whole thing, and a few others about the Autel AP200. I just ordered one, Amazon says it'll be here tomorrow.

I also read enough about the Dr Prius/Dr Hybrid and Hybrid Assistant apps that I decided to get the Panlong OBD2 Bluetooth scanner that Dr Prius recommends, it's only $13 with delivery tomorrow. Using that to monitor the traction battery is less urgent, but with the age of this Prius I want to know how it's doing. Also, we have a 2006 Honda Pilot, and that Panlong scanner should work with other apps to at least give me the basic ECU codes on the Honda.

I may also decide to get a P10 or P12 dedicated display for long-term monitoring, but at the moment I need the more complete diagnostic tool that the Autel provides, and can still do plenty of real-time monitoring with my phone while driving. I'll post tomorrow when I get the Autel working.