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pressure sensor for brake booster implausible signal
This is the code that I get now. All smoke tests come out negative on both sides of the engine . I have replaced the turbo boost controller in the front of the engine. That code hasn't come back. Temporarily removed the EVAP solenoid under the overflow tank that allows fuel tank venting into the intake. Temporarily blocked off that line that goes to the intake. Replaced the vacuum pressure sensor behind the passenger wheel splash.
I'm sure you guys are sick of me by now, but come hell or high water I am going to get this problem fixed. Just too nice of a car to keep parked in the garage. The closest Bentley dealership is over an hour away and I'd rather sell the car than go there.
For those who don't know, the car runs 100% until I get to the first stop light, about 3 minutes after startup. Then the RPMs drop to under 500, and the car goes into some sort of limp mode; no power, abnormal shifting and an engine light. MAF sensors both cleaned and both show equal on VAG live scanning. When I get back home, I hear the vacuum pump come on when I push the throttle, not when I push the brake pedal.
How many brake or vacuum sensors, check valves or solenoids are there that could be the problem? I'm just gonna replace them all. That way I can check that off of the list and move on. I have a RossTech and VAG. Any tests or anything specific I should look for?
This is the code that I get now. All smoke tests come out negative on both sides of the engine . I have replaced the turbo boost controller in the front of the engine. That code hasn't come back. Temporarily removed the EVAP solenoid under the overflow tank that allows fuel tank venting into the intake. Temporarily blocked off that line that goes to the intake. Replaced the vacuum pressure sensor behind the passenger wheel splash. I'm sure you guys are sick of me by now, but come hell or high water I am going to get this problem fixed. Just too nice of a car to keep parked in the garage. The closest Bentley dealership is over an hour away and I'd rather sell the car than go there. For those who don't know, the car runs 100% until I get to the first stop light, about 3 minutes after startup. Then the RPMs drop to under 500, and the car goes into some sort of limp mode; no power, abnormal shifting and an engine light. MAF sensors both cleaned and both show equal on VAG live scanning. When I get back home, I hear the vacuum pump come on when I push the throttle, not when I push the brake pedal. How many brake or vacuum sensors, check valves or solenoids are there that could be the problem? I'm just gonna replace them all. That way I can check that off of the list and move on. I have a RossTech and VAG. Any tests or anything specific I should look for? Thanks for any suggestions or flat out guesses.
What comes to mind is the vacume line from the rear passenger wheel well. This line is connected to the pressure switch that was replaced. The line has two functions. First function is for the 2 exhaust flaps. The second function is for the evap test function. The evap valve is near the suspension pressure pump under the rear cover.Smoke test the passenger wheel vacuum line. Make sure the exhaust flap small vacume tanks are in good shape. The vacuum pump running when accelerating is probably the result of the evap valve testing and not quite passing. Block the rear line after the new wheelwell sensor and see what happens. This is a test and not a solution. The evap test valve may be the issue.
Last edited by 1eapplebaum; Mar 4, 2023 at 02:10 PM.
Hello @2007Conti ,
Please explain what you mean by "all smoke tests on both sides of the engine", this sounds like you are doing multiple tests at multiple locations, the only locations I have seen are either in the drivers wheel well, or at the firewall center of the rear of the engine, and only either one would be used to do the smoke test, and at the same time, plugging up the turbo intake funnels on each side.
Johnny, I have done multiple smoke tests on both of the lines you have described. One for the majority of the vacuum system (access by pump behind the driver wheelwell) and the access on the back of the engine (for the EVAP system). I have not tested from the pressure sensor (behind passenger wheelwell) back to the rear wheel area. I'll try that next.
Really appreciate all of the help from you and 1eapplebaum
Just sent smoke to the back of the car through the line behind the right wheel. No joy.
Beginning to think this is going to whip me! Ready to start replacing any pressure sensor that could cause this. Already replaced the one behind the right wheel splash. If there are any others or anything else that you might think could cause this, I'm all ears.
Just sent smoke to the back of the car through the line behind the right wheel. No joy. Beginning to think this is going to whip me! Ready to start replacing any pressure sensor that could cause this. Already replaced the one behind the right wheel splash. If there are any others or anything else that you might think could cause this, I'm all ears. Thanks
Okay, now block the line to the rear after the sensor and drive it a bit. Does the vacuum pump run then, while accelerating? The car will be louder since the exhaust flaps will stay open. E
After taking 1eapplebaum's advice I capped off the vacuum line going to the rear of the car. NOW the pump comes on when I hit the brakes and not when I accelerate.
NOW the pump comes on when I hit the brakes and not when I accelerate. (Scratches )
Could be an issue with one of the grey turbo dump solenoids behind the engine. They can internally leak vacuum. Does the car make boost smoothly?(Please note I am not referring to the boost solenoids). Try pinching off the small vacume lines one at a time at the rear of the engine with the engine running and see if the vacuum pump changes behavior (while pumping the brakes). Also leave the rear line plugged. At Idle 6 +or- pumps of the brakes will normally engage the vacuum pump.
@2007Conti ,
Sorry, but I have to ask, as it's either the way that I am reading it, or it's not worded the way I would say it.
Did you actually remove the line off of the bottom of the sensor, and cap the port on the sensor itself, not cap the line going to the rear, as that line would have no vacuum, the sensor would, and a line would be plugged, so the language is confusing as to what you actually did, pictures would definitely help here.
@2007Conti ,
Sorry, but I have to ask, as it's either the way that I am reading it, or it's not worded the way I would say it.
Did you actually remove the line off of the bottom of the sensor, and cap the port on the sensor itself, not cap the line going to the rear, as that line would have no vacuum, the sensor would, and a line would be plugged, so the language is confusing as to what you actually did, pictures would definitely help here.
Johnny
.
Sorry for the confusion Johnny.
I left the sensor with vacuum still going "through" it and ended the vacuum going to the rear of the car. My hoses in that area aren't conventional because last year I bypassed the bad vacuum line by using Steve's copper line trick. I'll post a picture when I get the wheel back off of the car.
Hopefully I can clear up the current situation; The car is in one of two "modes" which I will call the good mode and the bad mode. The bad mode reminds me of a limp mode; very little power, zero turbos, erratic shifting in drive but fine with paddle shifters.
The good mode starts when I first start and drive the car. Full power, no vacuum pump with either brakes or throttle. Smooth boost from the turbos. Most of the time this lasts for a few minutes but can be as long as 15 minutes. The bad mode usually happens after a few minutes of driving and at the first stop light with brakes on but no vacuum pump running. I can barely feel something change; then the RPMs drop to below 500. Upon accelerating I can immediately tell that it has changed to the bad mode. Stays in bad mode until the next time I drive which is usually the next day after I try something else. A couple of days ago when I returned home in the bad mode, in park, the pump would kick on when I hit the throttle and go off soon after. Pressing the brakes didn't cause it to come on. Yesterday, when I was pulling out of the garage and stopped for a few seconds I could feel it go into the bad mode much quicker and the pump would cycle on with the brakes pushed one time, each time. In park it would not cycle on with throttle this time. Not sure if it was because it wasn't warmed up yet or what, but I didn't get to drive it in the good mode to warm it up.
Something is telling this car to go into this mode. It's a night and day change. Can't for the life of me find any kind of vacuum or intake leak which is what I feel is happening. I noticed some sort of spring door on the airbox that would allow more air to come into the box, probably under heavy throttle but that isn't when I'm getting a problem. The one airbox that I checked (passenger side) seemed fine and the spring loaded door seemed fine.
Sorry for the epic novel. Good thing I have a lift here in my garage or this would be twice as big of a job! I've gotten the removal of the wheels and wheelsplashes down to a science.
As always, I really appreciate you guys helping me.
Sorry for the confusion Johnny. I left the sensor with vacuum still going "through" it and ended the vacuum going to the rear of the car. My hoses in that area aren't conventional because last year I bypassed the bad vacuum line by using Steve's copper line trick. As always, I really appreciate you guys helping me.
Please do post a detail of the bypass. Did this issue occur immediately after the bypass mod? Also when a VAG auto goes Into limp mode there are stored codes for this occurrence and associated faults. So usually blocking of the rear line stops the vacuum pump running on acceleration, that didn't happen here....so more involved.
Last edited by 1eapplebaum; Mar 7, 2023 at 07:04 AM.
Please do post a detail of the bypass. Did this issue occur immediately after the bypass mod? Also when a VAG auto goes Into limp mode there are stored codes for this occurrence and associated faults. So usually blocking of the rear line stops the vacuum pump running on acceleration, that didn't happen here....so more involved.
Actually it did stop it from running on acceleration. Now it just runs when the brake is pressed. Each time it's pressed. Doesn't come on when I push the throttle at all now. I'll pull up whatever codes are stored.
008825 - Leak in Air Intake System
P2279 - 002 - - MIL ON
Freeze Frame:
Fault Status: 11100010
Fault Priority: 0
Fault Frequency: 2
Reset counter: 255
Mileage: 142740 km
Time Indication: 0
There is a possibility that the bypass is the root cause and inflicting limp mode. Might be worth reverting back to the old system although there will be a vacuum leak. Also delete all the codes. Start over and re scan after a few drive cycles .
