Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
So as the title says, Im working on a 2020 chevy trax with a hill start assist issue, or so it seems. The symptom is when on a hill and the assist engages and holds brake pressure to keep the vehicle still it doesn't always release the pressure after the pedal is released. As this is happening if I pull up manually on the brake pedal it will release. There's not a lot of slop in the pedal and I don't physically pull up very much to get it to release. but when i do that it acts normal and drives fine otherwise.
The kicker to me is as this going on the second I release the brakes when this symptom is happening while I'm looking at live data it goes no comm with the scanner. I went on a half an hr drive watching live data and it never goes no comm until hill start assist activates and I try to drive away normally. But it boots me every time.
One thing I haven't done is check freeze frame data yet. I will do that as soon as i get back to the car later today.
I do have some dtcs C0161 and B1527 are the ones that that pique my interest. I've seen some posts that say a BPP sensor, a master cylinder replacement due to swollen seals keeping the system slightly pressurized, and an abs unit have all been known fixes to this issue. Looking to get some insight so I can make a concrete diag on this and want to see what yalls next steps would be as I'm no diag master and am still learning. I've relearned the bpp in both the bcm and ecu. no change. Its shows active and not active when on the brake and off it respectively in live data. The Bpp sensor shows a change in voltage when applying break pressure and is around .49 volts showing with no pressure on the break. Shop key says up to 1v is normal when brake not depressed.
Geddy, I think I'd follow the C0161 if this were in my bay. From the code set criteria for C0161:
The electronic brake control module detects the brake pedal is not applied when the brake pressure is greater 15 bar (218 PSI) for 3 seconds.
The electronic brake control module does not detect that the stop lamp switch signal changed after driving the vehicle at a speed greater than 40 km/h (25 MPH) and performing three brake stops
I'd compare the BPP signal against the brake system pressure after stomping on the pedal a few times. I'm guessing there's gonna be some residual brake pressure there. That'll set C0161 AND cause the brakes to drag.
Having to pull up on the brake pedal would suggest something like a binding pedal or brake booster. Has anyone replaced the brake booster or master cylinder recently?
