What does this mean?

I'm assuming that you have a 2G. During summer season, a common problem is that the inverter coolant pump fails. This causes the inverter to overheat and the DC to DC converter will allow the voltage on the 12V bus to drop. The low voltage causes the brake and VSC lights to come on.

If your air conditioner does not blow cold air, this is another symptom supporting the likelihood that this is the problem, since the inverter powering the air conditioner compressor will shut down.

One way to assess whether the inverter coolant pump is running is to look at the fluid level in the container when the car is either IG-ON or READY. You should be able to see a step in the fluid where the rear is higher. Also, when the engine is off you should be able to hear the pump running; it is located near the driver's side headlamp assembly.

If the pump is OK, then another possibility is that the brake system has a problem.

Regarding the MAINT REQD light, this is just based upon a 5K mile counter, so perhaps your time has come to change engine oil?

It is normal for the dealer to quote a diagnostic fee to ensure you are serious that a problem is present; if the issue is covered under warranty then that fee should be waived.

 

Hi Ron,

If the inverter coolant pump is the problem, it is covered under the powertrain warranty of 5 years/60K miles. See the attached TSB for more info.

Regarding trying to replace the pump yourself, this would be a moderate difficulty DIY project. The main challenge would be draining and replacing the inverter coolant so that no air is left in the system. If you decide to take this on, I urge you to download the relevant repair manual pages at techinfo.toyota.com

Good luck.

 

Hi Ron,

Try disconnecting the negative terminal of the 12V battery for 10 minutes, then reconnect. It may be easier to remove the negative cable where it connects to the vehicle body.

If the warning lights remain on, then you will need a code reader that can retrieve the DTC and reset the ECUs.

 

Hi Ron,

Congratulations on saving ~$600 in exchange for a few hours of work! That sounds like a great tradeoff to me.

I assume that you drained and replaced the inverter coolant as well as the engine coolant? Regarding the engine coolant, did you open all three drain cocks (engine, radiator, and coolant heat recovery canister)?

I hope you used the pink Toyota SLLC when replenishing the coolant. How many gallons did you use: my guess is that 3 gallons were required?

 

Hi Ron,

Thanks for the detail on your coolant drain and replace. I didn't know it was possible to buy full-strength SLLC. I had a similar experience as you with respect to the canister drain passing most of the fluid that came out of the engine coolant loop.

Well, I flushed the brake fluid on my 2001 a couple of years ago. My procedure was to first suck out most of the old fluid in the reservoir using a rubber squeeze bulb. Then I filled the reservoir with fresh Toyota DOT 3 brake fluid.

I had my wife very gently depress the brake pedal and hold it slightly depressed while the car was IG-ON (so that the brake system would be powered up.) Starting with the rear wheels and then moving up to the front, I slightly opened up one drain cock at a time. That resulted in a large flow of brake fluid out of the drain cock, through a clear vinyl tube, into a glass jar. The old fluid was not that dark, unlike old fluid from normal cars, so it was hard to tell exactly when the old fluid was exhausted and the new fluid began. Then I closed the drain cock and had her release the pedal. I replenished the fluid in the reservoir and moved to the next wheel, and repeated until all four wheels were done.

The main concern is to ensure that no air gets into the system upstream from the brake wheel cylinders; for example, allowing the brake fluid reservoir to run out. If that happens, a dealer visit will be required to have the brake lines properly bled. I used two bottles of brake fluid and decided that was sufficient to declare victory.

One disadvantage of my method is that the new brake fluid may not flow through all portions of the brake actuator assembly. However, a big advantage is the relative low cost of my method.

The 2G brake system is more complex than Classic and I haven't tried this procedure on my 2004 yet. When the car has logged more miles I plan to try it out, after studying the repair manual to see whether modifications are required to the procedure.

Worst case, the procedure doesn't work, air enters the system, and I have to tow the car 5 miles to my local dealer for help. This would not be the end of the world, should that happen...

 

Hi Ron,

Is your new coolant red or pink? If red, it is LLC which has a 30K mile change interval.

If pink, and it really is 100% antifreeze (no distilled water), please advise the part number and pricing. I'd like to get some...

 

Hi Ron,

Thanks for looking into this.

SLLC is pink and has a 50K mile change interval after the factory fill coolant is replaced (100K mile for factory fill). I paid $21/gallon earlier this year for the 50%/50% mix at Tustin Toyota in OC.

LLC is red and has a 30K mile change interval. This is 100% antifreeze so it needs to be mixed with water.

 

Hi Ron,

Thanks for verifying that you used LLC, not SLLC. I used LLC in my 2001 since that was the factory-fill coolant at that time.

LLC is about 1/2 the price of SLLC when you consider that LLC must be mixed with water; however it needs to be changed at 30K mile intervals instead of 50K mile intervals. When you consider the value of your time, SLLC may be the better choice.

 

Patrick, I too, have a 2004 Prius with 91K miles on it and the VSC light came on last night.. Everything still works fine and I drove to work this AM with no problems. The inverter pump was replaced about 40K ago. Is this a recurring problem?
(One way to assess whether the inverter coolant pump is running is to look at the fluid level in the container )
Is the container the one that warns of pressure, between the engine and the "Hybrid Sunergy Drive" ?
Thanks,
Ed

 

Patrick, I too, have a 2004 Prius with 91K miles on it and the VSC light came on last night.. Everything still works fine and I drove to work this AM with no problems. The inverter pump was replaced about 40K ago. Is this a recurring problem?
(One way to assess whether the inverter coolant pump is running is to look at the fluid level in the container )
Is the container the one that warns of pressure, between the engine and the "Hybrid Synergy Drive" ?
Thanks,
Ed


I observed fluid moving in the above mentioned "Container" so I will try ungrounding the battery...
Ed

 

Hi Ed,

Yes, the inverter coolant reservoir is mounted on the side of the inverter which is facing the engine.

You could try disconnecting the 12V battery for a few minutes but that will not take care of an issue with the skid control ECU or other brake system parts, if the car has a real problem in that system.