Lost with code 0556 brake booster sensor failure

[Mac Arnold]

I have googled and searched the forum for over two weeks in regards to this code. It just started about 3 weeks ago and it has been driving me nuts. The first time I got the code, I added approximately 1 ounce of brake fluid and it cleared. Then 2 days later the same code went off again, I checked the reservoir and it was the same as 2 days prior, so I cleared the code. Then this last weekend it went off again, over the weekend I changed the oil and it cleared (which really had me scratching my head). Today on my way home from work I got the same code once again. I have checked the hose from the booster to behind the firewall and it seems ok. So now my my question is could it actually just be a temperamental sensor, or is there something I am missing? Again I have searched around and have checked everything posted in the last few years. Any further assistance would be greatly appreciated.

[Spec]

Man, that's an oddball. Hope you find a solution here, for everyone's sake.

[christianchevell]

The sensor might be telling you its time for a brake fluid change which if a ls3 with a manual and no separate reservoir for the clutch your most likely due from contaminants . NOT....but still a good idea with the age of your car , mine a 13 is about due and I use a separate reservoir.

If not wanting to go to the local tire store for a brake flush billed you could get a siphon bulb like I use on my clutch reservoir too at least change out what you can yourself, but if going for a flush/bleed its good time to upgrade to DOT 4..though the cap may say dot #3 and you don't want to mix the two..... if not that replace the sensor or clean it.

But being that its the booster its the vacuum tank and that's separate... so as in a old chevy the reservoir comes out of the booster so look around it for this and I would plug and unplug https://www.bing.com/shop?q=camaro+g...4EC6FF3099FF09 R & R if needed and check for vacuum leaks anywhere........

[ron123]

From what I read the Code 555/556 is NOT on the Hydraulic Brake fluid side, it is a code for a problem on the vacuum booster side (except in the rare case where brake fluid leaks in to the booster).
Did you tap in to a vacuum line for a catch-can or other mod? Maybe it is just a bad brake booster pressure sensor.

From Bestride.com - here is the full story:
P0555 (yourmechanic.com also lists this info for code 556)
Brake Booster Pressure Sensor Circuit Indicator

The PCM has detected a fault in the brake booster pressure sensor circuit.

Code Set Parameters
If the PCM fails to receive a voltage input signal from the brake booster pressure sensor that is proportionate to the decrease in vehicle speed required, a code will be stored and a malfunction indicator lamp will be illuminated. This problem normally occurs when the brakes are applied. Some vehicle models will require multiple ignition cycles with a failure of this nature for a check engine soon lamp to be illuminated but a code should be stored on the initial failure. If only the initial failure is exhibited, the code may be stored as a “pending code”.

Symptoms
Symptoms may include a hard brake pedal, increased effort required to depress the brake pedal, an illuminated service engine soon lamp, and a stored trouble code. In rare cases, the driver may experience no adverse drivability symptoms.

Common Causes
The most common cause of this code being stored is from vacuum leaks to the vacuum brake booster or a defective brake booster pressure sensor. Other causes may include shorted or open electrical circuitry and connectors, cracked or broken vacuum hoses to the brake booster, or a defective one way valve in the vacuum brake booster supply hose.

Common Misdiagnosis
While it is possible for the brake booster to fail, this condition is normally accompanied by a vacuum or hydraulic fluid leak. A vacuum supply problem, or sensor fault, are more likely causes but techs report that brake boosters are frequently replaced in error.

Diagnosis
The brake booster pressure sensor is designed to provide the PCM with an input signal reflecting the amount of braking assist pressure available for stopping purposes.
The PCM uses this input signal for the purpose of monitoring how much brake pressure is available to stop the vehicle at any given speed.
Brake booster pressure sensors are generally of a silicon diaphragm design.
A low voltage signal (typically 5 volts) and a ground signal are provided to the sensor.
The higher the pressure becomes in the brake booster, the less resistance the sensor provides and the greater the voltage signal is to the PCM.
If the brake booster pressure becomes insufficient, the resistance of the sensor becomes greater and signal voltage decreases to the PCM.
In this scenario, the PCM recognizes the low voltage signal as low brake booster pressure and a trouble code is stored.
Several tools will be instrumental in successfully diagnosing this code.
A suitable OBD-II scanner (or code reader) and a digital volt/ohmmeter will be most helpful in performing a successful diagnosis.
Begin with a visual inspection of all wiring and connectors.
Repair or replace damaged, disconnected, shorted, or corroded wiring, connectors, and components as necessary.
Always retest the system after repairs are completed to ensure success. If all system wiring, connectors, and components (Including fuses) appear to be in normal working order, connect the scanner (or code reader) to the diagnostic connector and record all stored codes and freeze frame data.
This information can be extremely helpful in diagnosing intermittent conditions that may have contributed to this code being stored.
Continue by clearing the code and operating the vehicle to see if it returns.
This will help to determine whether or not the malfunction is intermittent.
After the codes are cleared, test drive the vehicle to see if the code returns.
If the code fails to immediately return, you may have an intermittent condition.
Intermittent conditions can prove to be quite a challenge to diagnose and in extreme cases may have to be allowed to worsen before a correct diagnosis can be made
Proceed with your diagnosis with a visual inspection of the brake booster system.
Make sure that there is no fluid leaking from the rear of the master cylinder into vacuum booster.
Inspect all vacuum supply hoses used to supply the vacuum brake booster.
Also take a look at the pressure sensor, as well as the electrical wiring and connectors for signs of damage from corrosion, burning, or fluid contamination.
Repair or replace faulty components as required. If the vacuum source checks out and no wiring or connectors are damaged, then connect the scanner (or code reader) and make a note of all stored codes and relevant freeze frame data.
Test drive the vehicle and see if the code persists; if it does, then proceed with the diagnostic strategy. Disconnect the power brake booster sensor connector and check sensor resistance using the digital volt/ohmmeter.
Compare your findings with manufacturer’s specifications and dispose of the sensor if actual readings do not coincide.
If the sensor checks out, test the sensor connector for voltage and ground signals.
If no voltage and ground signals are detected, disconnect the PCM connector and perform a continuity test on the entire circuit in order to isolate a possible malfunction and repair open or shorted wiring as required.

[1Coopgt]

Originally Posted by Mac Arnold

I have googled and searched the forum for over two weeks in regards to this code. It just started about 3 weeks ago and it has been driving me nuts. The first time I got the code, I added approximately 1 ounce of brake fluid and it cleared. Then 2 days later the same code went off again, I checked the reservoir and it was the same as 2 days prior, so I cleared the code. Then this last weekend it went off again, over the weekend I changed the oil and it cleared (which really had me scratching my head). Today on my way home from work I got the same code once again. I have checked the hose from the booster to behind the firewall and it seems ok. So now my my question is could it actually just be a temperamental sensor, or is there something I am missing? Again I have searched around and have checked everything posted in the last few years. Any further assistance would be greatly appreciated.

Did you read this site .
https://www.yourmechanic.com/article...lerie-johnston

[Michaeljfl]

So, I keep getting a P0556 code also.
The dealership has replaced my brake booster sensor, the TCM, and the ECM.
It’s not loosing fluid but, when the CEL comes on it’s the same thing every time.
I have to stop the car usually with the brake pedal (front only) and my brakes.
Once stopped, I have to shut the car off. Plug in a code scanner and clear the code. Then pump my brake pedal multiple times until it stiffens up. Then it’s fine unless I’m driving more than 50 Miles. It’s actually so bad that the dealership loaned me a code reader to keep clearing the codes.

[29er]

straight from the gm manual

[Michaeljfl]

Originally Posted by Mac Arnold

I have googled and searched the forum for over two weeks in regards to this code. It just started about 3 weeks ago and it has been driving me nuts. The first time I got the code, I added approximately 1 ounce of brake fluid and it cleared. Then 2 days later the same code went off again, I checked the reservoir and it was the same as 2 days prior, so I cleared the code. Then this last weekend it went off again, over the weekend I changed the oil and it cleared (which really had me scratching my head). Today on my way home from work I got the same code once again. I have checked the hose from the booster to behind the firewall and it seems ok. So now my my question is could it actually just be a temperamental sensor, or is there something I am missing? Again I have searched around and have checked everything posted in the last few years. Any further assistance would be greatly appreciated.

I’m also having the same problem.
2015 2SS with 23k Miles.
The dealership has replaced the sensor twice.
Replaced the ECM.
Checked the intake pressure, holding at 20psi.
Now ordered a new brake booster.

[Michaeljfl]

Latest update.
ECU replaced
TCM replaced
Brake Sensor replaced
Brake booster replaced
ECM rewired
Oddly enough it went from happening once or twice a month, to nearly every time you start the car, and now the dealership can’t drive the car for more than 15miles without it happening. The dealership has had the car in service since July 16 and today is Sept 18.

[oballak]

Originally Posted by Michaeljfl

Latest update.
ECU replaced
TCM replaced
Brake Sensor replaced
Brake booster replaced
ECM rewired
Oddly enough it went from happening once or twice a month, to nearly every time you start the car, and now the dealership can’t drive the car for more than 15miles without it happening. The dealership has had the car in service since July 16 and today is Sept 18.

Hi, how did you solve the problem?

[AlanRubin]

The vacuum sensor is where the vacuum line is at the booster, where it pushes into
the rubber grommet. It also has a one-way check valve, so vacuum does not escape
the booster. Not all the V6s not have it, if any, but the V8s do. I have a booster pump,
but no sensor.

[Mouse330]

Inspect for a oil soaked or soft vacuum hose run between the engine and the Vacuum Brake Booster.

[AlanRubin]

Originally Posted by Mouse330

Inspect for a oil soaked or soft vacuum hose run between the engine and the Vacuum Brake Booster.

That doesn't happen with the Camaro.
That is a common issue with their SUVs, like the Yukon Denali, because
they have a belt driven vacuum pump, that is always turning. No oil
gets into the Camaro booster line. There is no SOFT line from the
engine to the booster, it's HARD line from the electric pump, to a "T" coupler
that a very small length of soft line goes to the intake manifold & to the
booster. There are no TSBs on oil in the lines for Camaro, but there is
for the 2014+ Yukon Denali, because I replaced one a few months ago, and
it is also all HARD LINE from the belt driven pump to the booster on the
SUVs.