I have a Nissan Sylphy 2002 with ( QR20DD engine ). The problem I'm trying to diagnose is:

When I'm sitting on a traffic or when I keep my brake pedal pressed all the way down, it keeps solid as it should be. However, when I shift to N or P and the RPM get increased a bit, my brake pedal moves a bit further to the down. Same thing happens when I pressing the accelerator pedal and RPM get increased (N, P or D whatever gear).

I have checked all the vacuum lines and they are good. Only thing I need to confirm is: Is this a sign of a bad Brake booster? My Brake booster seems to be leaking vacuum?

Randomly I'm getting P1806 - Brake Vacuum Sensor (low).

  • Welcome to Motor Vehicle Maintenance & Repair! What do you mean by, "my brake pedal moves a bit further to the down"? How much is a "bit further"? Is that a 1/2" or is it 1/2 way to the floor? Oct 7, 2017 at 10:53
  • Thanks for the comment. It goes down about 1 to 2 inches. Oct 7, 2017 at 12:00
  • Is the sensor expensive? I'd try to swap it just to see if the code goes away, temporarily ignoring the pedal aspect for the time being. Then I'd move on to other steps to resolve the issue once faulty sensor is ruled out. Oct 7, 2017 at 15:41
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    Sensor is not that expensive. It is a BOSCH sensor. I don't think that the sensor is faulty. I disconnected the brake booster line and tried to suck air. Brake booster isn't holding vacuum. Should it hold vacuum or should it have a small leak? Oct 7, 2017 at 15:45

1 Answer 1


To answer my original question, this could be an indication of a bad brake booster. However in my case, my brake booster isn't leaking vacuum. I confirmed it by hooking a multi meter to the vacuum sensor and the voltage I read was stable until I remove vacuum.

The other symptom I was describing is the pedal movement with the RPM increase also seems to be normal. I have checked this with many vehicles and they all behave same.

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