Nik01
Greenie N00B Member
Hi everyone,
I own a Mazda 6 MPS (Mazdaspeed 6) and I’m located in Italy.
Like many MPSs, mine had quite a lot of rust underneath, so I completely restored the front and rear subframes and basically the entire underside of the car. After replacing almost everything, I finally managed to put the car back together.
Unfortunately, I now have a major brake problem that I can't figure out.
I replaced all the brake lines with braided lines, installed new brake fluid, and bled the entire system. However, the brake pedal goes almost all the way to the floor.
If I pump the pedal twice, there is almost no resistance. On the third pump it gradually becomes hard, but the pressure does not stay there. The pedal becomes soft again.
I initially suspected the master cylinder, so I replaced it with a new ATE master cylinder, but the problem remained.
One thing I noticed is that I can hear a kind of hissing/air escaping noise around the ABS hydraulic unit/pump.
I have to admit that when I removed the brake lines, I stupidly left them covered with a rag but didn't actually seal the openings , so quite a lot of air probably got into the system.
I tried bleeding the system with the engine running, but it didn't make any difference.
I also tried bleeding the ABS unit directly:
- Bleeding at the ABS inlet
- Bleeding at the ABS outlets
- Then bleeding the wheels, starting from the rear right → rear left → front right → front left
The pedal is still almost completely soft.
Even after countless pedal pumps, sometimes the pedal becomes hard for a second, but then immediately loses pressure again.
There is another very interesting thing I noticed:
The front brakes hold pressure, but the rear brakes don't.
If I press the pedal, the front discs lock and remain locked.
The rear discs, however, lock for about one second and then become free to rotate again, as if the pressure to the rear brakes is not being maintained.
This made me suspect that perhaps the rear ABS valves are stuck or damaged.
To eliminate the master cylinder as a possible cause, I bought two pressure gauges and tested it.
The new ATE master cylinder seems to work perfectly.
If I remember correctly, I get around 100 MPa at both master cylinder outlets when pressing the pedal, and the pressure remains constant while holding the pedal down. With the engine off, it's approximately half that pressure, but again it remains stable.
So as far as I can tell, the master cylinder is fine.
I then moved the pressure gauges to the ABS unit outlets.
This is where things get strange.
On the rear brake circuits, I get very little pressure — usually around 10–30 MPa.
Occasionally, if I keep pumping the pedal repeatedly, the pressure suddenly reaches around 100 MPa for a few seconds, but most of the time there is almost no pressure.
It feels as if the ABS valves have somehow become stuck or damaged after sitting unused for a long time.
Because of this, I bought another Mazda 6 MPS ABS pump/unit from Germany.
I installed the replacement unit, but exactly the same problem remains.
I can still hear the same hissing/air escaping noise around the ABS unit.
I sprayed the whole area with soapy water to look for any external leaks, but I couldn't find anything.
I also checked the brake lines and calipers, but nothing seems to be leaking.
And the pressure gauge results are still the same:
Front → pressure builds and remains constant.
Rear → very little pressure and it doesn't remain.
Could that hissing noise actually be caused by ABS valves being stuck/open, or could there still be air trapped inside the ABS hydraulic unit that I simply cannot bleed out using the normal procedure?
I also bought a VCM II with Mazda IDS V130 because I wanted to run the ABS bleeding/actuation procedures.
Unfortunately, for some reason IDS will communicate with the engine ECU (I can see live data), but it will not communicate with the ABS/DSC module, neither with the original ABS unit nor with the replacement one.
There are no ABS or DSC warning lights when the car is running, so I assume the ABS/DSC system is at least passing its initial self-test.
I also tried using IDS and there were no fault codes, but I can't actually communicate with the ABS module.
As a final test, I put the car on a lift and spun all four wheels to see whether the ABS would activate.
Interestingly, ABS does occasionally activate.
When it does activate, the brake pedal feels completely normal for that moment, and I can clearly see that all four brakes are working correctly.
But most of the time the rear brakes still don't hold pressure.
So I'm completely stuck at this point.
Has anyone experienced anything similar on a Mazdaspeed 6?
Could this be:
- Air trapped inside the ABS hydraulic unit?
- A problem with the ABS/DSC hydraulic valves?
- A problem with the ABS pump itself?
- Something related to the electronic control of the rear ABS valves?
- Or is there a specific Mazda IDS bleeding/actuation procedure that I need to perform?
The fact that I've tried two different ABS hydraulic units with exactly the same symptoms makes me wonder if I'm missing something else.
Any ideas or suggestions would be hugely appreciated. I'm running out of things to test!
Thanks in advance!
I own a Mazda 6 MPS (Mazdaspeed 6) and I’m located in Italy.
Like many MPSs, mine had quite a lot of rust underneath, so I completely restored the front and rear subframes and basically the entire underside of the car. After replacing almost everything, I finally managed to put the car back together.
Unfortunately, I now have a major brake problem that I can't figure out.
I replaced all the brake lines with braided lines, installed new brake fluid, and bled the entire system. However, the brake pedal goes almost all the way to the floor.
If I pump the pedal twice, there is almost no resistance. On the third pump it gradually becomes hard, but the pressure does not stay there. The pedal becomes soft again.
I initially suspected the master cylinder, so I replaced it with a new ATE master cylinder, but the problem remained.
One thing I noticed is that I can hear a kind of hissing/air escaping noise around the ABS hydraulic unit/pump.
I have to admit that when I removed the brake lines, I stupidly left them covered with a rag but didn't actually seal the openings , so quite a lot of air probably got into the system.
I tried bleeding the system with the engine running, but it didn't make any difference.
I also tried bleeding the ABS unit directly:
- Bleeding at the ABS inlet
- Bleeding at the ABS outlets
- Then bleeding the wheels, starting from the rear right → rear left → front right → front left
The pedal is still almost completely soft.
Even after countless pedal pumps, sometimes the pedal becomes hard for a second, but then immediately loses pressure again.
There is another very interesting thing I noticed:
The front brakes hold pressure, but the rear brakes don't.
If I press the pedal, the front discs lock and remain locked.
The rear discs, however, lock for about one second and then become free to rotate again, as if the pressure to the rear brakes is not being maintained.
This made me suspect that perhaps the rear ABS valves are stuck or damaged.
To eliminate the master cylinder as a possible cause, I bought two pressure gauges and tested it.
The new ATE master cylinder seems to work perfectly.
If I remember correctly, I get around 100 MPa at both master cylinder outlets when pressing the pedal, and the pressure remains constant while holding the pedal down. With the engine off, it's approximately half that pressure, but again it remains stable.
So as far as I can tell, the master cylinder is fine.
I then moved the pressure gauges to the ABS unit outlets.
This is where things get strange.
On the rear brake circuits, I get very little pressure — usually around 10–30 MPa.
Occasionally, if I keep pumping the pedal repeatedly, the pressure suddenly reaches around 100 MPa for a few seconds, but most of the time there is almost no pressure.
It feels as if the ABS valves have somehow become stuck or damaged after sitting unused for a long time.
Because of this, I bought another Mazda 6 MPS ABS pump/unit from Germany.
I installed the replacement unit, but exactly the same problem remains.
I can still hear the same hissing/air escaping noise around the ABS unit.
I sprayed the whole area with soapy water to look for any external leaks, but I couldn't find anything.
I also checked the brake lines and calipers, but nothing seems to be leaking.
And the pressure gauge results are still the same:
Front → pressure builds and remains constant.
Rear → very little pressure and it doesn't remain.
Could that hissing noise actually be caused by ABS valves being stuck/open, or could there still be air trapped inside the ABS hydraulic unit that I simply cannot bleed out using the normal procedure?
I also bought a VCM II with Mazda IDS V130 because I wanted to run the ABS bleeding/actuation procedures.
Unfortunately, for some reason IDS will communicate with the engine ECU (I can see live data), but it will not communicate with the ABS/DSC module, neither with the original ABS unit nor with the replacement one.
There are no ABS or DSC warning lights when the car is running, so I assume the ABS/DSC system is at least passing its initial self-test.
I also tried using IDS and there were no fault codes, but I can't actually communicate with the ABS module.
As a final test, I put the car on a lift and spun all four wheels to see whether the ABS would activate.
Interestingly, ABS does occasionally activate.
When it does activate, the brake pedal feels completely normal for that moment, and I can clearly see that all four brakes are working correctly.
But most of the time the rear brakes still don't hold pressure.
So I'm completely stuck at this point.
Has anyone experienced anything similar on a Mazdaspeed 6?
Could this be:
- Air trapped inside the ABS hydraulic unit?
- A problem with the ABS/DSC hydraulic valves?
- A problem with the ABS pump itself?
- Something related to the electronic control of the rear ABS valves?
- Or is there a specific Mazda IDS bleeding/actuation procedure that I need to perform?
The fact that I've tried two different ABS hydraulic units with exactly the same symptoms makes me wonder if I'm missing something else.
Any ideas or suggestions would be hugely appreciated. I'm running out of things to test!
Thanks in advance!
