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Brake line replaced, can’t get pressure in the pedal
2007 e550 Facelift (no SBC).
Had a left rear (driver) side connection fail where the hard line meets the flex hose at the caliper. Put in a splice and new flex hose and everything is tight. Used a pressure tank to bleed all four calipers (though I only put 1l of brake fluid in the tank, so I had to de-pressurize the system and reload fluid after 2 calipers bled). No more air coming out out the calipers, but brake pedal still drops to the floor after bleeding the system out. I’ve seen various posts suggesting the ABS system needs to be bled using a star (or equivalent) system, but I’ve also seen posts suggesting that a pressurized system at 2 bar is sufficient.
The car currently will not accelerate as the traction control light (yellow exclamation point) keeps lighting up, and as mentioned, brake pedal drops to the floor. Basic Autel ODB scanner isn’t reporting anything related to brakes.
Any suggestions from the merc experts as to what is going on? Do i need to get a higher end tool like the icarsoft cr pro+ to initiate an abs bleed, or is there another way to bleed this sucker?
I’ve also seen threads that perhaps the seal in the master cylinder dislodged if you attempted to bleed the system the old school way (2 man, someone steps on brakes) which i did initially. Any way to check / fix the seal in the MC without buying a new one?
Get a better scanner. Literally. Cannot assist based upon the information provided.
Traction control light illuminating and brake pedal crashing to the floor should be lighting up all sorts of issues. You need something that will literally read the brake pressure at each caliper as a proper diagnostic system will do. Your car has advanced ABS/ESP so the sensors are there and providing data if you can read it.
When you say a pressure bleeder, assumption is that this is pressuring up the master cylinder from the fluid reservoir.
With pressure on the reservoir, any bubbles will be shrunk potentially making it harder to get them out.
A vacuum bleeder makes the bubbles bigger, not smaller. But then that is all backwards.
Suggestion is to do an old-fasion bleed. Fill the reservoir and get someone to push on the pedal while you open up the wheel cylinders (with hose into a container).
Just did a fluid chage on an E-350 this way and no issues. Pushed about 1 L of fluid through.
No codes and hard stiff pedal.
It sounds like you got air in the master cylinder.
Reviving this post. For Prime Day I picked myself up an iCarSoft CR+ Pro 2025 as an upgrade for my very basic Autel. Hoping this gives enough insight. Unfortunately it doesn't support the ABS bleed function for my Merc specifically.
Two basic issues with the car:
1) Brakes go to the floor while running. When the car is off, if you pump the pedal, pressure builds and holds.
2) ABS/ESP lights are lighting up like a Christmas tree around the holidays. Car won't accelerate because of all this.
Readings from the scanner for the issues above.
Re brake pressures:
While standing on brakes with car running
brake pressure 28.69 bar
A7/3b3 (left front pressure sensor) 29.56 bar
A7/3b5 (left rear pressure sensor) 11.87 bar.
2nd reading standing on brakes with car running (not as firmly)
brake pressure 19.4 bar
A7/3b3 (left front pressure sensor) 20.26 bar
A7/3b5 (left rear pressure sensor) 17.66 bar
Car running not on brakes
brake pressure -0.58 bar
A7/3b3 (left front pressure sensor) 0 bar
A7/3b5 (left rear pressure sensor) -0.29 bar
2) ABS/ESP related
Lateral acceleration while in PARK is reading -1.27m/s^2 : seems odd to me, but not sure if this is within margin of error.
ABS sensors are reading ~18.3 ohms. Does anyone know if this is within spec?
Rotation Direction of Left Rear Wheel = INVALID (moving or not)
RPM Left RPM Sensor Gap = INVALID (moving or not)
Wheel speed at right rear axle = 0km/h parked, bounces between a real reading and INVALID while moving.
To answer one of the previous questions, pressure was applied at the master cylinder at 2bar, while bleeding at each corner in the appropriate order. I'll try again using the old school method.
If there are any other specific codes I need to look for let me know.
Brake system pressures are not wildly out of line.
"2) ABS/ESP related
Lateral acceleration while in PARK is reading -1.27m/s^2 : seems odd to me, but not sure if this is within margin of error.
Over an eighth of a gravity acceleration. Enough to matter. Can you test the sensor? Possibly pull power to the sensor and see if it resets? When you pull power does the diagnostic system show the sensor is offline? Possible bad sensor but do not assume it is the culprit. Possible, but not definitive.
ABS sensors are reading ~18.3 ohms. Does anyone know if this is within spec?
Read the WIS referenced above.
Rotation Direction of Left Rear Wheel = INVALID (moving or not)
Possible wheel rotor issue? The toothed wheel pressed onto the axle. If not the toothed wheel, then the sensor or the connectivity.
RPM Left RPM Sensor Gap = INVALID (moving or not)
Ditto. Rust can seriously affect these. Can be replaced.
Wheel speed at right rear axle = 0km/h parked, bounces between a real reading and INVALID while moving."
Indicative of a bad connection. Clean all connections.
From the WIS for the 2007 E550:
Last edited by bbirdwell; Jul 28, 2025 at 09:35 PM.
Thank you for the response - followup questions below....in red.
"2) ABS/ESP related
Lateral acceleration while in PARK is reading -1.27m/s^2 : seems odd to me, but not sure if this is within margin of error.
Over an eighth of a gravity acceleration. Enough to matter. Can you test the sensor? Possibly pull power to the sensor and see if it resets? When you pull power does the diagnostic system show the sensor is offline? Possible bad sensor but do not assume it is the culprit. Possible, but not definitive.
Where is this particular sensor?
Rotation Direction of Left Rear Wheel = INVALID (moving or not)
Possible wheel rotor issue? The toothed wheel pressed onto the axle. If not the toothed wheel, then the sensor or the connectivity.
Is this the ABS sensor I mentioned with 18 Ohms or another sensor somewhere?
RPM Left RPM Sensor Gap = INVALID (moving or not)
Ditto. Rust can seriously affect these. Can be replaced.
Same question - is this ABS sensor?
Wheel speed at right rear axle = 0km/h parked, bounces between a real reading and INVALID while moving."
Indicative of a bad connection. Clean all connections.
Same question. Is this the ABS sensor?
EDIT: Adding comment that I pulled the sensors and cleaned them. A little dirty, but otherwise looked intact.
I will add, car was sitting for a while indoors, in my garage undergoing a replacement of the high pressure steering line that took way longer than it should have. The new part didn't align with the old part, but was the correct part # - a whole other story, that was escalated all the way to Germany). After that it sat outside for about 3-4 months unused, so rust could be an issue. Where am I looking for the rust?
I'll give the docs a read tomorrow, thank you for those...
Last edited by netracer; Jul 28, 2025 at 10:32 PM.
Reason: additional comment
The downloaded WIS will show locations of parts and diagnostic procedures. When I get home, I'll see about posting a tech document that shows locations. I've posted it multiple times before but don't have the links with me.
And yes, it appears both rear wheel speed sensors (ABS but Mercedes doesn't call them that) seem to be offline.
Last edited by bbirdwell; Jul 29, 2025 at 10:38 AM.
Out of curiosity, I looked that lateral acceleration on my car, and it's reading -0.50 m/s².
Also, I replaced both rear lines couple of years ago or so, and had hell of a time bleeding them. Must have gotten 2 litres of fluid through the system with the pressure bleeder, and pedal feel was mediocre at most. Drove a while, bled more with vacuum bleeder and feel was adequate. But I'm still not happy how it feels when the engine is running. Pedal will eventually go close to the floor if I stand on it. Engine off, and it's firm. Though I'm used to that pedal feel, but maybe I'll go old fashion way and get someone to pump the pedal and I crack the bleeder.
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