Code 21 Update

[Guest Double M]

The car is in the shop now for a week. I have a master Cylinder that I got from one of you out there, but it now needs Front Brakes, maybe rotors.

I could have brought it in a week earlier but a solid week of rain grounded me and my scooter so I had to drive it for 5 days with grinding front brakes.

I had another Brake Failure but this time I was prepared and studyied the symptoms. Every time this has happened it has been on a long trip on a hot day with serious bumper to bumper traffic.

Roger had a thought that it is affected by the heat and I am inclined to agree.

Anyways, I would feel the pedal "numbing" slightly before hand. I mean "numbing" as a feeling similiar to the way the pedal feels when the ABS actuates.

When the brakes actually fail, this is what happens...

The Yellow light is always on in my car, but the red brake light comes on and stays on upon failure.

The pedal travel is like this... The first quarter of travel is a dead pedal and feels as if there are no brakes at all. The next half of the way (the majority of travel) is "numb" with slight braking power and a slight vibration and a humming sound. Then the last qurater of travel is as if I just stepped on the brakes and I have only about an inch of travel and greatly dimminished stopping power, but it is always the same while in this condition. No way could I skid or do a panic stop, but I was able to stop and go in traffic.

So, I get to a parking lot off the Pkwy and let the car sit for about an hour, with the hood open, facing a nice cool Ocean Breeze. The Fluid level is at the full line during this, BTW. I try it every 15 minutes until about an hour later, the car starts up, the red light goes out and the Brakes are back to normal. I drove the car the rest of the day and the rest of the week w/o the problem happening again.

Then a week later the fronts started grinding themselves up and I put the car back in the shop, so I can get new fronts and see what / if the used master I have bought will help. My mechaninc has been very busy and is trying to free up and dedicate a bay to this project/fix.

I just wanted to update you all with these observations about the code 21 behavior being effected by the heat and a much more set of accuretly observed symptons.

[padgett]

Sounds like something is heating up and failing. Suspect the pump motor itself. Are all of the heat shields on the exhaust crossover pipe ? Did you replace the accumulator ?

[Guest Double M]

Yeah, the accumulator was replaced last year with one from Amazon. The code 21 was seemingly coming from that sensor on the M/C which is part of the whole assembly.

[Guest Mc_Reatta]

What is your engine temp while stuck in this traffic, and what temp thermostat do you have in the engine?

My first run-in with brake pressure failure in my Reatta was under similar circumstances.

As has been mentioned before, there are only so much pressure that can be stored in the accumulator, and constant applications of the brakes will overload it. Combined with high underhood temperatures when stuck in traffic with no airflow thru the radiator with a standard thermostat, and the temp increase of the fluid being pressurized by a constantly running pump can cause a water contaminated brake fluid to boil, allowing the pump to cavitate and then you will lose your breaking assist.

When the car and engine are allowed to cool back to a reasonable operating temp, braking returns.

Cure: Don't get stuck in bumper to bumper traffic on a hot day :mad:

or mitigate the other causes, flush contaminated brake fluid and replace with new, install a 180 deg thermostat, get cooling fans to run on high at a lower temp than stock.

Have a good accumulator installed. (at least you have that)

Modify driving technique to reduce time the brakes are applied. Bring car to a stop and shift into park so foot can be removed from pedal. When a gap opens in front of you, shift into drive and roll forward, then when necessary, stop car again and shift into park. Idea is to reduce the amount of applications of the pedal to a minimum to retain as much pressure as possible in the accumulator. Not the most natural method for driving in B to B traffic, and people will take advantage of the gaps that you let open in front of you, but it nicer to maintain decent braking function.

Edited September 16, 2011 by Mc_Reatta (see edit history)

[padgett]

One thingyou might try is keeping a steady pressure on the brake as much as possible - modulating the brake will exhaust the accumulator sooner.

[Rawja]

Angelo-

My whole saga for my similar circumstance is HERE

I'd bet real money you have the identical problem. In any case it'll at least give you some troubleshooting insight written by a non-tech.

Edited September 17, 2011 by Rawja (see edit history)