2002, 152K miles. Check Engine Light after long stop and go traffic jam on the side of a mountain.

The CEL can mean dozens of things. Can be as simple as gas cap not tight, bad O2 sensor, bad MAF, bad CAT. Once you get the codes post them here. Then you can get useful answers.

 

If your car still has the original "black bracket" electric coolant pump you should change it to the "new & improved design". See Inverter Coolant Leak - need help (Pics) | PriusChat

Make sure whoever installs it properly bleeds the inverter cooling system.

I recommend any Gen1 over 100k miles to change out this pump since it keeps the inverter electronics and transaxle cool...both of which can get damaged if they overheat.

The misfire errors may go away by themselves, but if spark plugs are old you should replace them or at least remove the ignition coils and check the plugs are snug...one car I came across had one spark plug unscrewed, guy was driving around on 3 cylinders.

 

I'm not sure what that would buy you. As long as the coolant in the inverter loop is still there, and pink, and wet, I don't think it's going to shout "problem!" to the dealership in any way. Are you thinking it's just due for a change anyway? When was it last changed?

Might be worth looking at related possibilities though. As 3pp pointed out, the inverter coolant pump can fail. Do you see flow in the inverter coolant reservoir when the key is ON? (You should be able to see the fluid level a couple cm higher at the front of the reservoir where the return hose goes in, compared to the rear of the reservoir where the fluid's pumped out. If the pump runs, do you hear any unusual noise? It's near the left-hand headlight, and should be very quiet, just a steady hum. Any 'fry'/'sizzle'/'squelch' noises could be bubbles of air circulating that need to be bled out.

Is anything blocking the radiators (either the big one for the engine, or the smaller inverter-loop radiator down in front of that)? Are a lot of the fins bonked over, restricting airflow?

In normal driving, natural airflow tends to be enough for cooling. Stop-and-go depends on the fans. Do you see the fans run? They should start immediately if you turn on air conditioning and the compressor runs. They should also start, even without A/C, if the engine coolant reaches 90 C (IIRC ... maybe it's 95). It takes patience to test that because "idle until temp reaches 90 C" takes just short of forever. It helps to watch the temp with a ScanGauge so you can at least see how slowly it's going up and you won't give up before it gets there.

I don't remember off the top of my head whether the inverter-loop temperature is also capable of starting the fans - seems like it should be, in case you're in stop-and-go where the engine isn't running much. But I don't have the books in front of me.

The fans have both a low and a high speed, which should really both be checked. (Without the books in front of me I don't remember what conditions you'd need to create to trigger high speed - maybe engine temp > 90 C plus air conditioning would do it.) I could imagine a tough-to-diagnose, only-happens-in-the-worst-conditions puzzle if the fan circuit had just the right problem to work fine on low but not to run on high.

Changing the subject, in what way did your power steering die? If it was the usual issue with glitchy torque sensor inputs, you only have 367 days left to get it fixed for free.

-Chap

 

Check the level of the inverter coolant resevoir before you drive the car any further. It's the skinny white/yellow plastic reservoir towards the drivers side near the center of the car..up near the window wiper tray and against the inverter. You should see reddish coolant between min and max fill lines.

You may got shocked (pun intended) at what the dealer charges for sparkplugs. Not that hard to replace yourself.
Only $9 each at Advance Auto for the exact same Denso plugs the dealer sells (but not in a Red Toyota box)
Denso SK16R11 part number 3324

 

The inverter coolant pump should be continuously running whenever the key is ON. If it isn't, you've found a good candidate for your problem. It's been reported in this forum that the pumps are likely to fail with age.

-Chap

 

Movement should be right away when key is ON position.
Take cover of reservoir and look inside while key is ON. It is safe to remove the cap and look inside if the car is not moving.

Take a long screwdriver or similar and hold it against the pump (under near drivers headlight). Do you feel it vibrating and/or hear it? If not, pump is toast.

Pump could also be working but poorly.
New pump should have considerably more flow. Make a mental note of how much flow you see now and after pump is changed. If you have a smartphone shoot a video to compare.

 

The pump has failed. Normal operation there is a barrier and you can see the two levels. With the cap off, you can see the turbulence. . . . Get it fixed before the next long trip or warm weather returns.

Bob Wilson