Can a P0442 CEL code effect my braking? Please help.

[ocmnelson]

I have a 2006 Explorer V6.
Ran perfect. On the way home Got a CEL P0442 code
P0442 - EVAP Control System Leak Detected (Small Leak)

Now the twist, I'm hoping this narrows down the problem. It started happening a day or two after the CEL light when on. Normally when I am coming to a stop and my truck downshifts into first gear from second it has its normal rev from downshifting. It now revs down but loses the back pressure somewhere. At the same instance my truck downshifts and revs my brakes loose pressure for a half second and then back to normal. ?????
So there is an Evap leak that is effecting my braking power or pressure.
By the way it is not my gas cap I had this issue earlier this year and bought a cap from the dealer and never had the problem again. I also had a new cat put in (if that helps) around the same time the gas cap was bought.

Please help.

 

[Town]

The EVAP leak is unlikely to be the cause of the braking issue. The EVAP leak is measured by applying engine vacuum to the tank and lines as part of the EVAP monitors check on the integrity of the fuel system early in each drive cycle.

The engine revving when coming to a stop is not related to the EVAP system since the purge valve is closed at that time. A leak in the engine side of the vacuum lines would create idling and driveability issues that you are not identifying.

I don't know why your engine would rev under the circumstances, but that would cause a drop in vacuum that should not affect the brake booster operation because of check valve at the booster. In all probability that check valve is not working, so any change in engine vacuum directly affects the vacuum at the booster diagphragm.

You can test the check valve at rest with the engine off by depressing the brake pedal. It should drop noticeably with plenty of vacuum applied to the diagphragm. It should operate the same way for a second depression of the brake pedal. If the pedal gets hard on first application of the brake pedal then the check valve has failed and needs to be replaced. It just connects to the hose and plugs into a grommet in the booster.

Good luck.

 

[ocmnelson]

Thank you for your reply.
The only reason I think the P0442 code and my failing brakes are going together is because I have never had a problem with the brakes. Rotors are good , pads, calipers, just changed the fluid. I got the CEL on Friday coming home from work. The next day I let my wife go to the store in my truck and she said my brakes did something funny. I got in and I could feel the same thing. I just think it is too much of a coincidence that the light when on and now my brakes are acting up.
So far the best bet will be for me to check the check valve at the booster. If there were a leak in the master brake cylinder or a vacuum hose connected to the brake booster or cylinder, do you think that can throw a P0442 code?
I can feel the pressure escape from somewhere. it is back pressure or something.

I will triple check all my rubber hoses. After that If I can not find the problem I guess I will take it to my dealer pay $100 bucks and have them smoke out my Evap system to find the needle in the hay stack.

I am pretty good at narrowing down the problems in my truck to the actual 1 bad part, this one has got me stumped

 

[Town]

Thank you for your reply.
The only reason I think the P0442 code and my failing brakes are going together is because I have never had a problem with the brakes. Rotors are good , pads, calipers, just changed the fluid. I got the CEL on Friday coming home from work. The next day I let my wife go to the store in my truck and she said my brakes did something funny. I got in and I could feel the same thing. I just think it is too much of a coincidence that the light when on and now my brakes are acting up.
So far the best bet will be for me to check the check valve at the booster. If there were a leak in the master brake cylinder or a vacuum hose connected to the brake booster or cylinder, do you think that can throw a P0442 code?I can feel the pressure escape from somewhere. it is back pressure or something.

I will triple check all my rubber hoses. After that If I can not find the problem I guess I will take it to my dealer pay $100 bucks and have them smoke out my Evap system to find the needle in the hay stack.

I am pretty good at narrowing down the problems in my truck to the actual 1 bad part, this one has got me stumped

No I don't think the P0442 is caused by the brake master cylinder or the brake booster or an engine vacuum problem.

In the red highlighted sentence you are dealing with 3 different systems. The brake master cylinder works with hydraulic brake fluid and there is no vacuum involved. The brake booster uses engine vacuum to help apply the brakes and since there is no continuing problem with the brakes or the engine operation I would think the engine vacuum is good. The brake booster check valve stores vacuum inside the booster to allow the brakes to operate when engine vacuum is low, that check valve may be faulty. The P0442 is identifying a leak in the fuel tank or vapour lines or EVAP cannister air intake solenoid or fuel fill piping. I cannot see how these 3 systems would be linked. The closest connection I can think of is a failure of the EVAP solenoid that opens to allow engine vacuum to lower the fuel tank pressure to a vacuum, but this usually results in a P0441 indicating a purge valve flow reduction due to either a solenoid issue or the EVAP hose to the intake being damaged (hole).

To check for the P0442, look at your fuel inlet pipe. It may have a leak. Check the hoses from the tank to the EVAP canister and to the engine firewall where the purge solenoid is usually located. You are looking for pinholes, literally. If you don't smell gas and cannot find any pinholes, or cut lines then clear the code and see how long it takes to come back. The dealer is probably going to pressurize the tank with smoke and look for a leak with the smoke. But this is not always successful, so you want a frequently occuring code to help the dealer diagnose the problem in one session.

Another issue is why the trans is causing the engine to rev on a downshift at low speed. In my experience a trailing throttle to slow the vehicle and then applying the brakes at low speed never causes the engine to rev. I don't think this is related to the P0442 either, but when the engine revs the engine vacuum is poor and the brakes need good vacuum. The check valve at the brake booster usually compensates for any loss of engine vacuum.

Good luck.

 

[ocmnelson]

The solution

Well, it was the infamous rear tone ring on the passenger's side. 400 bucks later my truck was normal. That was including an evap test. Appearently my gas cap was bad at the same moment my tone ring went out. Anyway just thought I would shed some light. And I just put on a new set of 265 70/16's. Love the tires and I got a 1.5" lift from my stock 235's. They are H/T's but I can't complain... all 4 for 100 bucks. A buddy of mine ordered too small of tires for his new lift...so he gave me a deal and I came up. Yay for me! Sorry for the late reply....