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Stiff brakes/ possible vacuum leak somewhere (C109D)
I recently changed the wheel hub assembly on my 5.4 3V F150 FX2 2WD. I initially had multiple codes pop all at once. I replaced the entire wheel hub assembly because the right front wheel speed sensor went bad and the bearing was the likely culprit. After replacing the wheel hub assembly (with sensor) all MIL went out. Till the next day. I was driving to work and the brake light came on (no abs). I ran a scanner and had about 4 codes. All the same as before replacing the wheel hub assembly. I cleared all the codes to make sure the computer wasn’t storing them. I thought all was good until the brake light came on again. So I ran the scanner agains and I have a C109D code ( low vacuum condition detected). I cleared it again and it came on again. So there is a problem here.
The brake lights only only come on while I’m driving and clear after i shut the truck down. It comes on randomly. There’s not a specific time. It’s always different. When it comes on it’s never when I’m pressing the brakes. I’m always just cruising at a single speed which makes it so odd. I ran my scanner for some live testing. I’ll post a screenshot below. You’ll see how the brake pressure is really low and it goes up when i depress it. The vacuum pressure is pretty constant throughout however I have yet to recreate the issue with the live scanner on. I’ll post a screenshot if I can capture that. Otherwise I have noticed a slight hissing while driving. Also not a constant. I can hear the vacuum page air when I shut off the truck. I can’t remember if that normally happened now because I haven’t payed attention to it but I’m pretty sure it’s not normal.
I have done the peddle test and the brakes hardly depress with the truck off if at all. When I depress the brakes and turn on the truck the brakes depress. When I rev the engine while depressing the brake peddle, the peddle depresses even further. When I release the gas the brake peddle pushes back a little bit. When i shut the truck off the brakes get stiff and it pushes the brake peddle back even with my foot on the brake peddle. I have no problems with braking distance as it’s not that bad as of now however I’m about to go on a road trip and I want to get this issue resolved now so I don’t have to on the highway with a 1 year old.
I have visually inspected vacuum hoses and blown into some of them. They look overall healthy. I have not used a fogger or the brake cleaner method. I suspect that I have a leak in the vacuum booster itself however I don’t know what that looks like and I can’t find information on it. I would like to run tests and diagnostic to make sure that is the culprit before replacing parts and find myself a step behind the issue. I don’t want to fix an expensive problem if the problem is a cheap fix.
I recently changed the wheel hub assembly on my 5.4 3V F150 FX2 2WD. I initially had multiple codes pop all at once. I replaced the entire wheel hub assembly because the right front wheel speed sensor went bad and the bearing was the likely culprit. After replacing the wheel hub assembly (with sensor) all MIL went out. Till the next day. I was driving to work and the brake light came on (no abs). I ran a scanner and had about 4 codes. All the same as before replacing the wheel hub assembly. I cleared all the codes to make sure the computer wasn’t storing them. I thought all was good until the brake light came on again. So I ran the scanner agains and I have a C109D code ( low vacuum condition detected). I cleared it again and it came on again. So there is a problem here.
The brake lights only only come on while I’m driving and clear after i shut the truck down. It comes on randomly. There’s not a specific time. It’s always different. When it comes on it’s never when I’m pressing the brakes. I’m always just cruising at a single speed which makes it so odd. I ran my scanner for some live testing. I’ll post a screenshot below. You’ll see how the brake pressure is really low and it goes up when i depress it. The vacuum pressure is pretty constant throughout however I have yet to recreate the issue with the live scanner on. I’ll post a screenshot if I can capture that. Otherwise I have noticed a slight hissing while driving. Also not a constant. I can hear the vacuum page air when I shut off the truck. I can’t remember if that normally happened now because I haven’t payed attention to it but I’m pretty sure it’s not normal.
I have done the peddle test and the brakes hardly depress with the truck off if at all. When I depress the brakes and turn on the truck the brakes depress. When I rev the engine while depressing the brake peddle, the peddle depresses even further. When I release the gas the brake peddle pushes back a little bit. When i shut the truck off the brakes get stiff and it pushes the brake peddle back even with my foot on the brake peddle. I have no problems with braking distance as it’s not that bad as of now however I’m about to go on a road trip and I want to get this issue resolved now so I don’t have to on the highway with a 1 year old.
I have visually inspected vacuum hoses and blown into some of them. They look overall healthy. I have not used a fogger or the brake cleaner method. I suspect that I have a leak in the vacuum booster itself however I don’t know what that looks like and I can’t find information on it. I would like to run tests and diagnostic to make sure that is the culprit before replacing parts and find myself a step behind the issue. I don’t want to fix an expensive problem if the problem is a cheap fix.
07-03-2019, 01:10 PM
Stiff brakes/ possible vacuum leak somewhere (C109D)
