Help Diagnosing Persistent BRAKE, ABS, VCS, and ((!)) Lights

I've had my 2007 Toyota Prius for ~5 years now, and it has given me rather little trouble. However, I've now got an issue that I need help diagnosing.

First, here's the relevant history...

1. My car was functioning just fine, with no warning lights.
2. I went on vacation for about 10 days, during which time my car was idle, sitting in the driveway.
3. I returned from vacation, and I drove the car to a local restaurant, not noticing any warning lights.
4. Leaving the restaurant, I returned to my car, and turned it on following the usual procedure. I immediately noticed that the BRAKE, ABS, VCS, and ((!)) lights were illuminated, with the BRAKE light glowing red, and the others glowing yellow/orange.
5. I drove the car home (slowly and carefully) on local roads (i.e., no highways).
6. I started the car again the following morning, and the lights were still present.
7. After googling the issue, I concluded that the explanation might just be a weak 12V battery, which seemed plausible given that the car had sat idle for 10 days, and that the battery was at least 5 years old.
8. I measured the voltage across the terminals of my "12V" battery with a voltmeter. Multiple measurements gave anywhere from 11.8 V to 12.2 V.
9. I also noted that the voltage measured by the car itself in the diagnostics screen was 11.4 V.
10. These measurements led me to conclude that the battery's performance was borderline at best, and that I needed to replace the battery to rule it out as the cause of the warning lights.
11. I removed the old battery, bought a new one (same part number) from my local Toyota dealer, and then installed the new battery myself.
12. I measured the voltage with my voltmeter: 12.8 V. I also measured it using the car's diagnostics: 14.8 V.
13. I again started the car, hoping that the warning lights would not reappear. Unfortunately, they did.
14. I've ordered an OBDII port reader online. It's supposed to arrive tomorrow.
15. Reading other threads on PriusChat, I learned how to get the "blink codes" from the car using the janky paper clip in the ODBII port trick. I got one code from the ABS light, one from the VCS light, and one from the ((!)) light. The codes are as follows:
    1. ABS: 42
    2. VCS: 45
    3. ((!)): 64

Based on what I've read on other threads, my understanding is that the 42 and 45 codes are general warning messages that don't give me much information. However, the 64 code corresponds to DTC C1343, indicating a "Rear Hydraulic System RH Malfunction".

I have requested a copy of the Repair Manual from my local library, but it will be a few days before it arrives. So, in the meantime, I wanted to ask this community for guidance. In particular, I'm interested in opinions on the following:

1. Is it plausible that there's really nothing wrong with my rear hydraulic system, and that DTC C1343 was raised simply because of low battery voltage?
2. If the theory above is correct, since I've already replaced the battery, that should fix the root cause. Accordingly, if I somehow clear the DTC codes, they shouldn't return. On the other hand, if the above theory is incorrect, then I almost certainly haven't fixed anything, and clearing the DTC codes should make them go away only temporarily. Bottom line: it seems that I have nothing to lose by doing a test where I clear the DTC codes and see what happens. Any thoughts to the contrary?
3. Where is everyone getting their Toyota Techstream tools from? When I search for this product on Amazon, I see a large number of vendors, most of which look rather sketchy. For example, most warn that I'll have to disable anti-virus software to use the device, which makes me uncomfortable. Are there any Toyota Techstream tools which don't require disabling anti-virus software?

 

I ordered this one, because it claims to have the ability to read and clear codes associated with ABS: "ANCEL AD610 Plus ABS Airbag Bidirectional Test OBD2 Scanner Diagnostic Tool, with ABS Auto Bleed SAS Calibration Oil Light SRS EPB Reset Engine Code Reader". You can find the exact product by searching for this string on Amazon. (Looks like this forum doesn't allow me to post the link.) If it turns out that the tool doesn't meet my needs, I'll return it.

I would happily order one packaged with Toyota Techstream if I could find one that doesn't require me to disable anti-virus software on my computer. (See question #3 in my original post.) Any recommendations?

 

Thanks for weighing in, ChapmanF!

You said:

Since you did not list a failing battery as one of the possible causes, can I assume you are confident that this is not the cause?

Also, you said:

Is it possible for an average citizen and non-mechanic like myself to purchase Techstream from Toyota?

 

Update: My OBDII port reader arrived in the mail. I used it to confirm the presence of DTC C1343. I then used the tool to clear the code. However, I found that it reappeared as soon as I depressed the brake pedal. So it appears that the battery was not the problem. :\

Now I guess I'm left waiting on the arrival of the Repair Manual at the local library. In the meantime, is there anyone out there with a copy of the Repair Manual kind enough to tell me what it says regarding DTC C1343?

 

Thanks for your help, ChapmanF and SFO! I've got another interesting observation to report...

My Ancel OBDII port reader allows me to see live sensor measurements. In particular, I can see the live measurements of four sensors titled "FR Wheel Cylinder", "FL Wheel Cylinder", "RR Wheel Cylinder", and "RL Wheel Cylinder". When I just sit the car without my foot on the brake pedal, these four sensors read as follows:



When I step down on the brake pedal, the values associated with FR, FL, and RL increase. However, the "RR Wheel Cylinder" measurement remains the same:



To me, this suggests that one of the following two scenarios is true:

1. The hydraulic fluid routed to the right rear wheel is not being appropriately pressurized when I step on the brake pedal, or
2. The hydraulic fluid routed to the right rear wheel is being pressured just fine, but the sensor is not measuring the pressure correctly.

Do you agree with this conclusion? Are there any other scenarios you can think of that might explain my observations?

To try to distinguish between the above two scenarios, my next step is to try the following experiment:

1. Elevate the right rear wheel with the jack.
2. Remove the parking brake.
3. Confirm that the right wheel spins freely (by hand).
4. Depress the brake pedal.
5. Check if the righ wheel spins freely.

If the right wheel spins freely, that suggests that Scenario 1 is true.
On the other hand, if the wheel does not spin, that suggests Scenario 2 is true.

Please let me know if you have other ideas!

 

While waiting for my wife to return to help me with the experiment described above, I've made another interesting observation...

My Ancel device also gives me live measurements of the currents through the solenoids responsible for controlling the brake hydraulics. When I'm sitting in my car, with my foot off the brake pedal, the SLARR, SLARL, SLRRR, and SLRRL currents all read as 0 A.



However, when I step on the brake pedal, the SLARL and SLRRL currents both jump up, while other two stay at 0 A.



The SLARL current is fleeting; it quickly goes back to 0 A, even while my foot is still on the brake. The SLRRL current remains elevated until I remove my foot from the brake.

I've included this observation just for completeness. However, the main point is that the SLARR and SLRRR currents (both corresponding to the RR wheel) do not respond to me stepping on the brake pedal. I believe this is consistent with Scenario 1 in my previous post. If the solenoids that are supposed to pressurize the RR wheel cylinder are not active, it makes sense that the pressure in the RR wheel cylinder remains flat.

So, now the question is: why are those solenoids inactive? If anyone has any theories, please feel free to share!

 

An unexpected plot twist...

Reading the repair manual, I came across the following: "The voltage between the terminals of the brake actuator assembly may become 0 V due to the fail-safe function when the ECB warning light comes on (malfunctioning)."

This got me wondering if the lack of current in SLARR was, in fact, due to the fail-safe function, induced by DTC C1343 being raised. To test this theory, I cleared the code, and then again tried to measure the SLARR current when I stepped on the brake. Sure enough, I could see current.

I thoroughly expected my stepping on the brake to cause DTC C1343 to be raised again. But it didn't. I stepped on the brake several more times (with varying levels of force) to see if I could get DTC C1343 to appear again. It didn't. Furthermore, I am now able to see the reading associated with the pressure in the RR wheel cylinder increase when I step on the brake.

I even restarted the car and tried again to get DTC C1343 to resurface by stepping on the brakes. Nope.

So I'm thoroughly confused. It seems very unlikely that I fixed the problem with my experimental poking and prodding today (looking inside the brake drum, disconnecting and reconnecting the brake control power supply, and so on). Yet, I can't get DTC C1343 to reappear. So I guess I'll just keep my fingers crossed that the code doesn't reappear. But, if it does, I'll investigate further.

 

Thanks for weighing in, mr_guy_mann!

Your suggestion is timely, because, just yesterday, I drove my prius around the block, periodically stomping on the brakes to (a) ensure that they worked and (b) see if I could get the dash lights to come on again. Sure enough, the third or so time that I stomped, the warning lights came back on.

I'm going out to the car now to confirm that it's still DTC C1343. Assuming it is, I'll see if I can generate time plots of the pressure sensor voltages... Stand by...

 

Confirmed: DTC C1343 has returned.

As before, it seems that the presence of DTC C1343 prevents solenoid SLARR from activating, because I can't measure any current through that solenoid, nor can I affect the pressure in the RR cylinder (by stomping on the brake) until I clear that code.

However, once I cleared the code, I was again able to measure current through the solenoid and varying cylinder pressure when I stomped on the brake pedal. Here are some plots showing the results. It does seem that the pressure in the RR cylinder tends to be a little bit slower to rise than the pressure in the RL cylinder.

Does that look like the sort of delay you'd expect if there was an air bubble in the RR hydraulic line? Should I try to bleed the line?

 

So I obtained a copy of the "Haynes Repair Manual" from my local library, but it says basically nothing about how to bleed the brake hydraulic lines. So I followed the procedure shown here:

.

In so doing, I drained my brake fluid reservoir from MAX to about halfway between the MAX and MIN line.

I also removed the brake drum on the RR wheel so I could look at the insides. Nothing was clearly amiss to my untrained eye (see images below). I turned the "star wheel adjuster" to ensure that the brake shoes were close to the drum but not dragging.

Unfortunately, this did not resolve the issue. DTC C1343 returned shortly after I started up the car and pumped the brakes a few times. Also, as you can see in the attached time series plot, the lag between the RR cylinder pressure and the RL cylinder pressure seems like it might even be more pronounced than before.

Anyone have any advice?