dash lights on with repeated hissing noise

Hissing would seem to me to indicate a leakage of pressure in the brake actuator pump. This is the pump that runs when one initially steps on the brake pedal to start the car. It keeps cycling to replenish the pressure that is leaking. These pumps have been known to fail, so it would not be a surprise on a car with that many miles. The change out procedure is given in a post here on PC, or on youtube videos.

Your description makes this more likely mechanical in nature. It could be the ABS ECU, but there is no way to be sure. See below.

If the car is off, then the HV battery is completely disconnected, so no high voltage is present. There is no point in disconnecting anything other than the 12V battery for brake work. The glove precaution is IMHO nonsense, more a product of this litigious world than a real safety need. But then I know my way around high voltage systems.

You need to get the DTC's read for the problem in order to proceed. I would recommend getting the mini VCI from eBay, since you will have some work to do on the car. Otherwise you can pull the blink codes from the ABS system. Procedure is here:
Traction Control Alarm Malfunction | PriusChat

Please list the codes. If the problem is indeed the brake actuator pump, see if the dealer will get a used one for you. Otherwise, check with autobeyours.com for a part. If your time is cheap, you could swap the ABS ECU just to see, since you have it already. It is a simple plug in part, once you get into the dash.

 

I'm not an expert on this, since I'm working on my 1st one. I've got an 06 with about 139,000 miles. The 1st problem I had was the display unit went out at 133xxx mi. I changed it out. Not long afterward the car didnt want to start and it had about all the warning lights on. I heard the same water gurgling sound and never figured out what it was. I changed the 12v battery. It started and all the lights came back. Found out that the HV battery had a bad cell. I'm trying to wrap up a balance charge on all 28 modules, which I learned from here. Lots of good info here! Hope you don't have the same problem.

 

1. It sounds like the brake actuator pump is not holding hydraulic pressure, which is why you hear the motor running for a short period, repeatedly. You would need to obtain the DTC from the skid control ECU to have more insight into the problem.

2. The Toyota repair manual advises using the insulated gloves when working on the traction battery, because Toyota is not interested in having anyone suing them due to carelessness during the traction battery replacement procedure, resulting in electrical shock. So you'll have to decide what works for you. However, the traction battery is not the issue here.

3. Certainly the Bentley manual will be better than Haynes, but your best bet is to subscribe to techinfo.toyota.com and download the needed repair manual pages.

 

At minimum, the 12V battery needs to be fully-charged, then let it rest overnight and see what your voltage readings for #1 and #2 are. Since the battery was replaced 10 months ago, maybe it just needs to be charged. If it has failed, you should be able to get a warranty replacement.

I agree that it is a reasonable step to replace the skid control ECU given the very large number of fault codes you retrieved. However pls note that you may later find it is also necessary to replace the brake actuator pump.

The skid control ECU is much easier to replace than the brake actuator pump so you'd might as well start with the ECU. If the brake actuator is replaced, that will require the brake fluid to be replaced by a Toyota dealer or independent who has access to the Techstream diagnostic laptop or equivalent, so that the actuator valves can be opened as needed when purging air out of the lines.

 

Not all of those blink codes make sense. However 69 is "Accumulator Leak Malfunction" which fingers the brake actuator assembly, as suspected. 22 and 24 are about loosing pressure in the front solenoids, which is saying the same thing.

The others are unclear, but seem to be about power supply issues. I think that the car sat for a while before you got it, and the 12V went a bit flat. These sealed batteries don't like that so well. While the long drive should have charged it, perhaps there is sulfation, and the battery needs a few equalization charge cycles to fully recover.

With a 12V having high internal resistance from sulfation, the voltage at start up drops too much while the ABS system charges up, and that can trigger some of the blink codes you are seeing. So I would not be concerned about them yet.

But there is a clear agreement that the brake actuator assembly is needing to be replaced. As pointed out, one needs Techstream to do it. Once that has happened, you can go from there. Keep us posted.

 

First, try charging the battery overnight, and see what happens.

Then, if you decide the battery is bad, look at the date code. If it is less than one year old, your local Toyota dealer might give you a break on a warranty replacement even though you don't have the purchase receipt.

How long did it take you to drive 300 miles: 5 hours or less? That is not enough time to recharge the 12V battery.

After you have a fully-charged 12V battery, clear the DTC in the skid control ECU (via the jumper in the OBD-II socket) and see what happens. If you still have a problem, it is reasonable to replace the brake actuator assembly.

 

Please ask the Tech what the "inf code" is for C1256. This is an additional freeze frame that gives more insight into the problem. The C1256 means "Accumulator Pressure Low", which means that the brake ECU is finding the pressure in the actuator is lower than spec after it has run the pump. I am guessing that Techstream would not be able to calibrate the linear solenoid if the pressure is actually low.

 

Given the presence of DTC C1256, was the brake actuator assembly actually replaced? If so did the tech see anything wrong with the installation?

 

Too bad you don't have a known good skid control ecu to test with. There are several on ebay for $60-$80


That being said I heard about a gen two with the linear control valve code you have that was fixed with a new actuator. Did you look at technical service bulletins regarding the codes yet?

 

I suggest that you check the relays providing power to the skid control ECU and the brake actuator. Remove each relay, use a decent digital ohmmeter to identify the coil terminals, and apply 12VDC to those terminals. Then use the digital ohmmeter to measure resistance across the switched terminals. The resistance should be 0.5 ohms or less (after accounting for resistance in the ohmmeter leads.)

You can find the electrical wiring diagram for your model year at techinfo.toyota.com so that you don't have to guess about what relay does what.

 

I would just check for power at the skid control ecu before going to the relays. I think no power at that ecu would result in no communication with that ecu not a single specific code.
Could incorrect bleeding make that code appear? That question would be answered in the tsb part of the Toyota info site.

 

I would buy a few used parts if you are really stuck. The dealer uses the shot gun approach why shouldn't we. Time is money. $500 in junk yard parts should cover every part of the abs brake system.
I fixed a complex dual carb mid 80's honda once by replacing 5 or 8 sensors and ecus in one fell swoop. I paid like $100 at the junk yard for the whole group of parts. A local honda specialty shop quoted $1500 to get to the bottom of it and described all the labor involved in trouble shooting the feed back carburetors. My point is, If you have access to cheap parts save some time and order several parts in one sitting. You can always resell what you do not use.