Greetings, New here...looking for some help with the problems in subject line. Any advice, directions etc are appreciated. Not very familiar with hybrids, but trying to learn. 2010 Prius w/ 235k miles Problems/conditions: -The brake booster pump (correct term?) runs/cycles every couple seconds until car is turned off. I can hear a noise in the area of the brake booster when car is off, and the car has shown before the trouble code related to the leaking accumulator (but oddly is not showing it now). -Separately, car constantly shows "Check Hybrid System" and has the P0AA6 code. Upon first startup, I can drive it with no abnormalities for a short distance (1/4 or 1/2 mile) but then something strange happens: the brakes no longer will regen correctly while braking, and the traction battery level indicator begins to drop noticeably. It should be noted that there is no braking trouble prior to this happening, everything is normal until the trouble begins. I note that once this braking trouble occurs, as I brake or coast, instead of it registering on the regen bar as normal, it indicates on the right side of the regen bar, as though I was using power while braking/coasting. I hope I'm writing this clearly. I'm guessing this is a direct result of the leaking accumulator? -Traction battery is only several months old (GreenTec auto) and charged; I have a grid charger to keep it full. But the CHS message displayed both before and after the new battery. -12V battery a month old and charged. -Getting frustrating. Questions: 1. Can a leaking/malfunctioning brake system in these cars lead to/cause a HV battery isolation fault, seeing that the regen system is connected to the battery in some way? I wonder if these 2 troubles above are related in cause. 2. I don't have Techstream to read the P0AA6 subcodes; can someone direct me how to get it on a laptop? 3. Are there any known 2010 Prius isolation fault items I could check right away to eliminate anything off the top? 4. Brake accumulator: where to obtain besides Toyota? Any refurb units or any such options out there? Thanks for any assistance. I've used this forum in the past and am grateful for the previous advice, now would be so glad to get some help on these specific problems. I confess I have not yet fully researched these 2 problems on this site yet. Hoping someone has experienced this before. Standing by to give more info if needed. Thanks, Eric
You have two different issues. The often-running booster pump and the code for leaking brake pressure are a simple mechanical issue with worn-out mechanical brake parts. These parts commonly wear out. Many were even wearing out much earlier than they should have, and Toyota had a service campaign for that, but it's over now. Wearing out in a fifteen-year-old car with 235k miles is just wearing out. Usually the cause of that problem is in the upper item of the two shown here. Many people with the problem will replace just the upper item and find the problem fixed. Sometimes it's the lower item. Some people, budget permitting, will just replace both items to not have to think about it. Your P0AA6 code indicates a completely different issue. You are noticing an effect on braking only because the brake system is notified of hybrid-system trouble codes, so it knows not to try to do regen. That's the only connection, though; the high-voltage isolation fault is otherwise nothing to do with the brakes. Techstream isn't the only way to read the INF subcodes. There are other scan tools or phone apps that can do that. Autel AP200 gets a fair amount of good press around here.
Thank you for the inputs/clarification. At the moment I cannot see any subcodes, I will be trying again with a friend's snapon scan tool later today. For the time being, I have been using a "megger" to test the frame wire and HV circuits off the inverter for insulation resistance. I am new to the tool; I read through the user guide and made certain to disconnect the circuits from energy sources, but I'm getting readings on the AC and MG1 circuits that I don't understand. The frame wire and MG2 check out according to the directions; no changes in resistance. The AC and MG1 circuits do not hold at the highest value of resistance as the other circuits do when tested, and start at a low reading, rapidly counting upwards. I see from the HV system diagram, the MG circuits are related to the transaxle. I wonder if anyone could assist with interpreting or advising on meggering the HV circuits, to test for the isolation fault code I have. I'll continue checking for subcodes but wanted to test circuits while waiting on this tool... Thanks
A megohmmeter is a specialized instrument that uses higher voltages for testing. At the higher voltages being used, things happen that you might not be familiar with from everyday experience. In most cases where people post here that they are thinking of buying a megohmmeter, I recommend that while they are waiting for it to arrive, they read Megger's pamphlet A Stitch In Time at least once. The information is important for using the instrument safely, as well as for interpreting what you see when you use it. Most of the instruments affordable enough for PriusChatters to be buying them are not going to come with that information; if they come with a page showing how the battery goes in, that's luxury. You don't usually think of wires having capacitance, but they do have a little. When you've got as much length of wire wound up as an MG winding, it adds up. Your initially low megohmmeter reading counts up quickly while that capacitance is getting charged up to match the instrument test voltage. While that's happening, energy is being stored in that capacitance. Once that steady value increase kind of stops, but the reading still continues to increase more slowly, the high voltage is storing energy by polarizing the insulation around the wires. When that uptick stops, you've got a final reading. For safety, as you go to disconnect your meter after the test, you should remember the time you spent watching energy get stored into the winding capacitance, and then into the insulation polarization. That energy is still there. (!) Most megohmmeters have a display that reverts to showing voltage once you release the test button at the end of the test. That way, you can watch the voltage decrease to a safe level as the stored energy is being bled off, before you go reaching to unhook the leads. As for a megohmmeter reading of the air conditioner compressor, I'd be unsure just how to interpret that on a gen 3. The gen 2 Prius A/C compressor was just a bare 3-phase motor, so you'd be taking a reading just like it was a smaller MG. But in gen 3 they moved its motor control inverter circuit right into the compressor itself, so if you megger that orange connector, you're taking a reading of some whole elaborate electronic circuit inside there.
