Brake pedal hard & warning lights on at start up/No Codes

Abs accumulator is leaking down, at some point it will become enough out of spec to set a code. Eventually you will just have no power brakes. It's a fairly involved repair as you have to pull the inverter to do it. It took me a lazy day, if you aren't comfortable doing it, find a tech in your area who is knowledgeable about the prius. If you mechanic doesn't know what's wrong with it now, he is not your guy.

 

It seems that ScanGauge is only capable of reading codes and data from the ECM (engine control module). There are a whole bunch more ecu's on a Prius. Now if you use the search feature on this forum you can learn about "flash codes" - where you can use a small jumper wire to (carefully) connect two terminals of the OBD2 data port, turn the car on, and some of those ecu's will flash the warning lights on the dash if there are fault codes present.

Usually, the ecu's will keep those codes in memory as "history" codes for quite some time (or until a scantool or loss of 12V battery power erases them).

Count which lights flash how many times ("long" flashes are for the tens digits and "short" flashes are the ones). Then you can post what codes you find, and can look them up in the service manual (search for how to get that as well).

That said, your symptom sounds like a serious failure in the braking system- loss of high pressure that's needed to well, operate the hydraulic brakes and perform ABS and traction control functions. If that is what happens you would have a fail safe system that "connects" the brake pedal to the front brakes - no boost, no ABS, no rear brakes. Braking takes much more force on the pedal and stopping distances increase alot.

Please don't drive this car until you have it fixed.


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I think there are only long and short pauses between the flashes ... the flashes themselves all have the same length. Short pauses go between the digits of a code, longer pauses between codes.

So flash flash (pause) flash (longer pause) flash flash flash (pause) flash flash would be 21 and 32.

I think it can do better than that; I believe it uses the simple strategy of broadcasting a "hey, anybody got codes?" on the car's CAN, then showing you whatever comes back.

It was semi-crippled on the Gen 1 Prius, which was such a crazy pre-CAN mishmash of different comm networks that some of the ECUs had to be reached by resetting the connection with different baud rates, and some by passing messages to them through other ECUs, and pretty much nothing but Techstream had a realistic chance of doing all that.

The later generations adopted CAN and are more standard, which should be an improvement. On the other hand, there are still (at least in Gen 3, I don't remember for Gen 2) multiple different CANs in the car, with some ECUs connected to more than one and acting as bridges. So some weirdness is still present.

ScanGauge also has this "XGAUGE" feature where you can teach it to send additional queries and commands if you know how to encode them. I'm pretty sure PriusChat members figured out how to use it to get HV ECU codes (and even INF codes) for Gen 1, for example.

 

I'll just say this, as many of these cars had this problem, if they can't diagnose it, you don't want them touching your car. There is even warranty extension documentation about it. I would talk to the service manager about the diagnostic fee, pay enough to cover the tech's time though they obviously gave it to the wrong guy, and find an independent in your area that can handle it.

 

There are some known problems with the brakes, but this doesn't sound quite exactly like the ones I'm familiar with.

It really ought to be possible to get trouble codes though.

With access to Techstream, I would consider setting up datalogging/graphing of the brake fluid pressure sensors, and getting a capture of those during this initial startup weirdness.

 

Just going by the ad copy from the scan gauge website - I didn't see anything about scanning other systems beyond engine controls. Lots of "features" that all seem to be based mostly on generic OBD2 engine data. Could be wrong (I often am).

Said it before, if a scan doesn't return a list of what specific ecu's that it was able to communicate with, then "no codes found" is pretty much useless in my book.

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