Brake Booster Pressure Sensor
 

On Cold (20F) Morning When I start the car BRAKE WARNING SYSTEM yellow Light come ON.
On my Snapon Solus Pro Diagnostics Scanner code P0556 Came out Brake Booster Pressure Sensor CKT Range/Performance.
Sice I still have warranty took it to dealer to check the sensor and if need it they will replace with new one.
i would do it my self but why pay 100 dollars for sensor.
I'll update what happen. because my RDX still at the dealer. they gave me 09 RL to take home.

I know this is an old post but if you're still on the site can you tell me the outcome of this error code.

Thx

Same thing has been happening to me the last few extremely cold days!
No noticeable signs of a problem (brakes work fine) but amber brake system light is on.
Please let us know what you/dealer found!

Thx

Same thing happened to us last week when the temps were in the -20s. The light came on a few times then but we didn't notice any problems with braking and the light hasn't come on since.

Yeah I have had this same problem over the weekend. It went away on Sunday but came back this morning. Its been in -30 range over night so i'm going to wait it out till it warms up on Thursday before doing anything about it though.

Brake booster problems
 

I have had this problem as well...same issues temp-wise and all...different code though P180xx (don't recall the entire code) but says the brake booster may not be working properly and may be harder to press...brakes seem ok...took to the dealer THREE TIMES...after reprogramming the code, checking brake pump, they replaced the sensor...now 6days after having it left it for the weekend the amber light is on again...I am furious. Seems to be somehow cold weather related? The dealer disagrees. I will let you know what happens next.

I had this code for the first time ever last weekend when on vacation in Pagosa Springs, CO, when the temps hit 12 degrees in town when we left for the ski resort 35 miles away around 9am. The RDX was slow to start, TPMS was giving me warnings at 26 PSI, Navi screen took forever to brighten up, and the brake booster warning did not turn off until the temp got above 25 degrees (or maybe the engine bay warmed up enough to turn off the code?). Haven’t seen the brake booster error code since that one day and the daily low temps have been above 25 degrees.

I have about +65,000 miles and the brake fluid has never been flushed. Could extremely cold temps and maybe water/contaminates in the brake line(s) caused this error code? If a brake flush is not the answer, how much does it cost to fix?

***UPDATE***

Acura tech said the Brake booster sensor voltage was out of specification. It was reading a higher voltage of +7 volts compared to a normal of about 4 volts. Acura replaced and tested. I just have to see if it is A-OK the next time it gets below 10 degrees. I have 66,000 miles on the RDX and wasn’t covered under the powertrain warranty.:ugh:

Parts: 46401-STK-A01 Sensor, $171.30
Labor: $100
Total: $271.30+free car wash

This was my first unplanned out of pocket expenses for my TSX and RDX. Other than routine maintenance, tires and batteries, both cars have pretty much trouble free and reliable.:thumbsup:

Bad but not super bad $. Hope it stays clear at low temp for you.

Po556 code
 

My girlfriend has a 2009 Acura RDX and that code flashed when it was cold as well. Last night was -10 degrees here in Michigan and she got into the car again this afternoon and the code is gone,
so I do also believe it is related to cold weather

I haven't had any issues since getting my brake booster sensor replaced back in 2012. I really don't know if replacing the sensor is the 100% solution because my RDX haven't been left out overnight in teens or below since.

I had a similar problem like that wile back, only on extreme cold.
I replaced the DOT and the problem went away, coincidence?
My guess was that to much humidity was already on the DOT and with the change the yellow light went away.
I havent checked at that moment if there's was a code since the light would go off after a wile.

Gosh, I have this same dang issue I think. I've only noticed this cold temperatures, but my wife's brake pedal is starting to feel soft. I did find two codes though:
P16DB & P16DD

https://acurazine.com/forums/1g-rdx-.../#post16392522

If feels soft, check for leaks right away.
Air must us got in.

Update: Brake pedal isn't actually that soft (I think I was just being paranoid), but the codes have returned today in 60 degree weather. I think I may just bite the bullet and bring our RDX to my local Honda dealership to diagnose this issue.

I would go to acura our RDX is special first of its kind unicorn.

Just my two cents ...

If anyone else is still following this thread, I found the solution to my problems:
https://acurazine.com/forums/1g-rdx-...-p16dd-977678/

Here are also a few links that describe each code:

Code P16DB
https://www.autocodes.com/p16db_acura.html

Code P16DD
https://www.autocodes.com/p16dd_acura.html