Multiple qs: Aux Battery, ECU control, LED assembly

What DTC was logged by your car? That will show whether #2 is required or not. Given your driveability symptoms, I agree that a failed inverter coolant pump seems likely.

I can believe that #1 is required assuming that the 12V battery is original equipment, just because your car is six years old. If the DC/DC converter in the inverter shut down due to overheating, the car will depend upon the 12V battery to provide power to the electrical systems, which includes the braking system. Your battery apparently was not up to the challenge which is why you lost braking power.

<By the way, your story provides an excellent example of why the Prius needs to have a 12V battery in top condition. A marginal battery will let you down in an emergency situation.>

You can easily verify the failure of #3 yourself, and if it is bad then you can either buy the part from one of the Toyota dealers that offer a 25% discount from MSRP or buy a salvage part - if you can DIY install.

Regarding #4, at your car's odometer reading a throttle body cleaning would not be out of line, but that would not have caused your car's symptoms. You can buy a spray can of throttle body cleaner for $10 and DIY, there are posts on this forum regarding that activity.

 

MSRP of the 12V battery is $139, so if you call around you may find a better price.

I again question whether your symptoms would be caused by either a bad 12V battery or a skid control ECU. Without the DTC there's no way to answer the question.

In any event, the skid control ECU could be replaced DIY as a salvage part, recommend you download repair manual info at techinfo.toyota.com if you are interested. That ECU is located near the steering wheel column.

 

DTC C1300 "Malfunction in ECU" is logged by the skid control ECU and refers to that unit.

It is reasonable for you to have the 12V battery replaced by the dealer. Then let's see if the car will run and the braking system work. If it does, I suggest that you take it and check the inverter coolant pump to see if it is running (I've posted a few times on how to check its proper operating condition.)

If the pump is not running then its replacement is obvious. If the pump is running then I think you should drive the car to see whether DTC C1300 reappears. I don't recall a prior report of this code.

Actually, skid control ECU replacement is not DIY because it will be necessary to initialize the linear solenoid valve and calibration. So, you'll probably have to rely upon dealer service for that. However it would be reasonable to wait for a repeat occurrence of that code before spending $1.8K on the repair. Also you might be able to call around to see if you can get a lower price at a different dealer.

Or you could buy a salvage part, install it, then tow the car to the dealer to have this initialization and calibration service performed. Regarding the part number, you can consult toyodiy.com which is an on-line parts catalog, or else inspect the ECU currently installed in your car.

 

I agree with Patrick, replace the 12V battery, then see if the DTC C1300 reappears before agreeing to the ECU replacement.

 

Like all of us, you are interested in saving money, so follow Pat's suggestions to the letter.

 

1. Have you checked the inverter coolant pump to see if it is working? If not, please do that now:

- Make the car IG-ON where all instrument panel warning lights are on and the car is not READY. (From IG-OFF, press the POWER button 2x without depressing the brake pedal.)

- Open the hood and look for the inverter coolant pump behind the driver's side headlight assembly. Listen for the sound of it running, which sounds like an aquarium pump. Also look at the inverter coolant reservoir and see if you can see turbulence in the fluid (open the cap and look inside if needed.)

2. If the pump is not working, then replace it.

3. If the pump is working, then pls find out what DTC has been logged, and if it still is C1300, then decide whether you wish to obtain a salvage part from a salvage yard, or a new part from the Toyota dealer.

 

No, but a bad 12v battery could possibly cause an invalid C1300, or some other spurious DTC. The low 12v battery or a bad Skid Control ECU would not cause an inverter pump failure. The inverter pump failure is relatively common failure on higher mileage Gen 2s.

Some mechanics are not very familiar with the Prius, and some mechanics just follow the DTC without thinking about what other failures might induce a DTC.

Definitely get the inverter pump fixed.

 

+1

 

Thanks for the update. Failure of the skid control ECU is quite rare, so I think you'll be good to go after the inverter coolant pump is replaced. Nevertheless, if C1300 reappears you now know how to handle it.

 

If you have a digital multimeter, then you could make the Prius READY, have a helper depress the brake pedal or place a large weight so that it will hold the pedal down, find the wires providing 12V to the brake LEDs and measure the voltage to ground. Then compare to the voltage provided to the center brake light. All measurements should be ~13.8V.

 

I have no answer for you other than to say that I have the identical problem. Center light OK but left and right either dim, not working at all, or, one side is working OK. Erratic. You may already know you can't replace the LED's alone; you have to replace the entire tail assembly. Dealer quoted me $230 at the parts department today. Aftermarket versions are much cheaper ($88). Dropping it off at the dealer tomorrow to have them look at it. I asked the service guy if he's noted other Prius' coming in with the same problem but he was not offering anything. I get the feeling this happens more often than he was admitting.

 

I have commented on this before. The Prius brake lights are poorly designed. The LEDs are put in parallel and series with 1 series resistor. If 1 LED in 1 string fails, the current goes up in the other strings, and they then fail quicker. You can purchase tail lights from Toyota online for about $170. When I checked nearly 2 years ago, there were no after market tail lamps. $88 sounds like a good price for them. There is only 1 ground wire for all the bulbs in the assembly, so if the other bulbs work, then the failure is definetly in the tail light assembly. Changing the taillights is an easy DIY project. You just a screw driver and a socket wrench.