VSC, ABS, and that exclaimation mark light - went away after parked in a garage

Did you check if your inverter coolant is circulating?

 

I think your inverter coolant pump is not working (or if it is working, not very well). If you can DIY replace the pump, do a search for my post about: http://priuschat.com/forums/gen-ii-.../65173-how-replace-inverter-coolant-pump.html

At minimum, if you have a digital voltmeter available, measure voltage across the 12V battery when this problem reoccurs. You'll probably find the voltage is below the usual 13.8V, which shows the DC/DC converter has shut down due to overheating. This causes the warning lights to come on as the brake/skid control system is very sensitive to incorrect voltage on the 12V bus.

 

Who knows why the master warning light did not come on. Normally it should turn on, which gives you a hint to look around for the other warning lights.

The inverter coolant pump is covered under the 5 year / 60K mile warranty.

 

very new to site, but I have an 05 with 206000 miles. Just got the VSC ABS and (!) light after leaving a movie on a hot night. Vehicle also has an ear-splitting electronic noise that starts about 5 min after starting. Noise goes off 1 min after shut down. Ran codes with nothing coming back, but hear i may need to go to Toyota for their tool. 12 V battery and inverter pump checked good as well, although I notice my mileage is down to about 42 from 45 although it is horribly hot in Arkansas this week. Any help would be most appreciated!

 

The noise is intended to warn you that the brake system is significantly impaired. A generic OBD-II code reader will not pick up DTC logged by the skid control ECU.

I suggest that you have the car towed to your local Toyota dealer for diagnosis and repair.

 

Mr. Wong, thank you so much for looking at this! I had the vehicle towed to an independent Toyota shop and they ran a diagnostic. I don;t have them in front of me, but one was 1252 which I believe has something to do with the ABS? They used one hour of diagnostic time but said to investigate further they will have to dig into the engine bay behind the inverter which will be standard labor rates. I will post all the codes tonight, but do you think it might be prudent to obtain a used ABS ECU and possibly a VSC ECU to put in since all the parts would be out? I'm just trying to make the vehicle trade-in safe at this point. Thank you again!

 

DTC C1252 means that the brake booster pump within the brake actuator assembly is running more than it should. Potential trouble areas include the brake actuator assembly, two relays (ABS MTR and ABS MTR2) and the associated wiring harness. The skid control ECU (which provides ABS and VSC functionality) is not on the list of potential trouble areas.

Hopefully a relay is the problem since those are inexpensive and easy to replace. The brake actuator assembly is very expensive and time-consuming to replace, so if that is the problem I hope your shop has techs who are trained on the Prius (non-hybrid vehicles do not have this brake design.)

 

Hi again, I got the full list of codes which included the 1252 hydro boost pump motor malfunction and 1253 relay malfunction. There is also a 1300 ECU malfunction and 1121, both of which are pre-existing I believe. I notice that I have little to no regenerative braking as witnessed by the lack of the little green cars on the energy info screen, so will try the relay route first as you suggested. He said that in order to do the wiring, a lot of things have to be moved, so we may order a used ABS assembly first before tearing things up. Thank you so much for helping us narrow it down!

 

Yes, DTC C1300 means that the skid control ECU is bad, but hopefully that is a spurious code caused by the same root issue that is producing C1252/C1253.

DTC P1121 means that the engine coolant flow control valve is stuck. This is a separate problem, unrelated to the brake system issue that you have. This valve routes engine coolant to the cabin heater core and/or to the coolant heat recovery canister.

 

Hello, I'm hoping for advice. I have a similar issue to what kmpask describes above:

-Lost brake power, with shrill brake alarm, emergency brake light, ABS, VSC, and (!) lights all on. Fortunately I was on a residential street and by standing on the brake, could glide to a stop.

-My regular, trusted auto shop duplicated the problem and reported a failed hydro-boost motor. At least one tech *can* work on a Prius, but they're wary of such a complex job.

-So I got the car to the local dealership, which has a shaky reputation at best. This morning they reported that the brake actuator assembly needs to be replaced, and since it's under the inverter it'll take a lot of labor time. They quoted me over $3000 for the repair.

From what I understand, a brake actuator assembly replacement is the worst possible scenario for the problem, in terms of both parts and labor. Given this dealership's history I have no reason to trust their diagnosis. Can anyone here suggest odds, or what questions I should be asking?

(I'll give the error codes as soon as I can find them out...)

Error codes: DTC 1252, 1256, NC 1300

 

The dealership's diagnosis is consistent with the logged DTC and is also consistent with the opinion expressed by your regular trusted auto shop. The motor is located within the brake actuator and the entire actuator must be replaced.

If you believe that your local dealership has a shaky reputation, can you find another Toyota dealership with a better service reputation to do the work?

 

Mr. Wong, my local dealer says my issue is the Skid Control ECU. Is this part any easier to replace than the ABS accumalator? They want $1700 for the part and $320 for labor, so am thinking about taking it to the local Toyota specialist and see what he would charge. Thank you in advance!

 

Yes, the skid control ECU is located near the steering column behind the dashboard. Perhaps you can see if the local specialist would be willing to install a part from a salvage vehicle. Good luck.

 

Hi again Mr. Wong!

I finally found a skid control ECU and had the Prius towed to the shop, but the mechanic took it on a test drive and said it lost all braking ability, even with him standing on the pedal, and he finally stopped it by doing a curb shot. He re-did the scans and found a C1256 code and believes it's something to do with the ABS accumalator vs. the skid control. Is there any chance bleeding the brakes might help restore the pedal feel before I get the accumalator looked at?

Thanks as always!

 

Yes, DTC C1256 points to the brake actuator assembly. The troubleshooting flow shows how to measure resistance on certain pins on the actuator wiring connector. Then it shows how to power up the brake actuator to see whether the voltage reading of the pressure sensor remains flat. If the voltage drops, then replace the brake actuator. If the voltage holds flat then replace the skid control ECU.

I would not think that bleeding the brake lines would be helpful unless you know that air was introduced into the hydraulic system. Good luck.

 

Hi Mr. Wong, just wanted to say thank you so much for all your help! I got the used skid control ECU off of Ebay for about $120 and my local independent charged 3 hours to install for a total cost of about $350 vs the $2k plus the dealer wanted. Car is back to normal and my only issue is researching how to replace the right side HID ballast now after a chat with Maumelle's finest last night about my non-working light...lol