Zombie thread revival!!!!
arty:
I have the same symptom in my 2010 MMH, but it's extremely intermittent (like once a week). Trying to determine whether it's the check valve (like Irakli's issue) or if it is the vacuum pump itself. Hoping, of course, it's the former- but I'm unsure due to a lucky instrumentation observation.
I set up Forscan Lite on my phone, and have been driving around capturing a few ABS PIDs- and I finally have 'caught it in the act'!
I captured both vacuum sensors, as well as the vacuum pump on/off, and VAC_BST_ST, which I thought would be when the ABS requested the engine to turn on. But that's actually ABS_REQ_VAC, which I didn't collect. But I'm pretty sure I knew when this happened as the dashboard bonged the the Brake light went on.
To summarize the functionality: hybrids (2009+) have an electric vacuum boost pump to keep vacuum in the brake vacuum lines when running electric without the ICE. There's two vacuum sensors (I think they're both at the same spot- there's two because redundancy) and if the vacuum pressure drops too low, the electric vacuum pump is turned on. The failsafe is when the vacuum pump can't keep enough vacuum in the line. It then signals the ICE to start up to supply the crucial vacuum pressure, illuminates the brake light, and sets the C1015:64-68 in the ABS module. (I'll post a youtube at the bottom of the very excellent mechanic who 'taught' this to me- I think he's been know to post here a time or two also).
Anyhow, back to my story. You see the chart below. I plot the vacuum pressure (I only listed one, as they both stayed consistent with each other, ruling out a sensor failure). The blue is vacuum pump on/off. You'll see it hums along as planned- vacuum drops, pump turns on, vacuum back 'up', pump turns off. then about two thirds of the way through...you see the pressure take a precipitous dive. Pump turns on- vacuum continues downward (the wrong direction). After a longer-than-usual pump 'on' period, the pump is briefly shut off. Oddly at that point the vacuum seems to stabilize. Pump turns back on- vacuum starts dropping again. Eventually (near the end of the really long 'pump on' period) the ABS mod calls for the ICE to fire back up, and then vacuum recovers. Unfortunately since I had the incorred PID being captured I can't tell exactly when the ICE was triggered- was it while the pump was still on, or does the ABS shut the pump off as soon as it trigger the ICE?
Anyhow, my question was going to be: if the check valve was faulty, should vacuum recover with the ICE? But I think typing this out- and a long look at Iraki's picture above- has led me to the conclusion that yes, the engine side check valve stuck open could definitely cause the observed behavior. Engine side check valve stick open/vacuum pump dums out into the engine instead of where it's supposed to in the braking system (I have no clue how that side of it works, I just know it needs vacuum!)/ICE gets fired up and presents the proper vacuum in the line /Pump side check valves does what it's supposed to and closes off that side of the lineset due to pressure differential. I was just backing up into my driveway when this occurred- now I know I should've gone back out around the block and kept logging data to see if the situation ever recovered by way of the check valve un-sticking. But maybe once this happens the ABS keeps the ICE engaged and it's not reset until an engine cycle?
Anyhow, here's my graph followed by the excellent video. If anyone sees a flaw in my thought process, please let me know! After I found the TSB I had actually procured the replacement lineset and I have an appointment with my mechanic two days from now for him to troubleshoot and probably install that replacement lineset. It was going to be a "just to see" replacement, but I think it's probably the correct fix at this point. I don't think that vacuum pump can be intermittent like that, could it?