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Lou P. master tech
Lou P. master tech, Mercedes Technician
Category: Mercedes
Satisfied Customers: 3663
Experience:  15 years master certified 100% fix rate and have access to factory radio codes, wiring, and instructions.
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We have a 2003 E320 Mercedes Benz sedan, rear wheel drive

Customer Question

We have a 2003 E320 Mercedes Benz sedan, rear wheel drive (not AWD) 152k miles and the instrument information display shows in ALL RED with "WARNING" "REDUCED BREAKING EFFECT" START ENGINE & "WARNING" LONGER STOPPING DISTANCES" START ENGINE.
(same status whether driving or parked)
What I do know: This car has the SBC braking system.
-Just installed new 12 volt Back up Battery(old one was completely
dead) related to the SBC system. (this did not change anything on
the display).
-Just installed new main 12v battery located in trunk.
(no change in display).
-Just installed all new rotors, brake pads (pad sensors were all good
and verified with DVM meter and show good. (no change in display).
My conclusion is a bad SBC unit(MB paced a 10 yr warranty on the SBC unit after numerous failures were reported, this car is out of that warranty period) The unit seems to be OK, cycles on/off when brakes are pumped, etc.
Note: I will not be satisfied with answer if same as above.
Problem two:
Also, electronic door lock/unlock feature, when pressed, door lock relay chatters repeatedly(possible bad diode on related relay?) If you agree on possible faulty relay, please identify where it is located.
Please advise
Submitted: 4 months ago.
Category: Mercedes
Expert:  Lou P. master tech replied 4 months ago.

Hello. Most likely the lifetime expired on the SBC unit. Have you checked fault codes ? I know you already assume the SBC unit is faulty but without a fault code why would you want to assume we can check other items in the system. Please advise how you wish to proceed. I want to help but you seem already on the offense. I am here to help. Lou

Customer: replied 4 months ago.
Apologies if sounded offensive,
Things checked so far:
1. brake pad sensors good.
2. foot parking break switch checks good (12v when parking brake off & open circuit when engaged)
3. OBD2 reports zero fault codes when connected to port and igition key in on position, same results when car is running)If you are asking " Have I checked the fault codes?, are you referring to fault codes stored in the SBC unit? or fault codes via the OBD2 port mentioned above?
STAR software utility program via laptop interface at the SBC Unit, then no, I am not a dealership.
Customer: replied 4 months ago.
OOps......see below for additional tasks completed:1. new main battery replaced.
2. New SBC battery replaced.
Expert:  Lou P. master tech replied 4 months ago.

Ok so the obd port is where you should check for codes. It sounds to me like the code reader you have will only check the engine module. So you will have to get a star diagnostic machine or high end autel scanner to read the rest of the codes in the system. As for the small battery that is the internal interior battery. Not sure why everyone thinks that is for the SBC strictly. Most likely you have the infamous c249f fault code. And the brake switch is not the parking brake switch it's the brake pedal switch above the brake pedal. Your model may have it hidden behind sound insulation. If the brake lights work ok then most likely the brake switch is ok. Do you have a means to get the code ?

Customer: replied 4 months ago.
will the below unit work? copy/paste link below to brouser: so, I will go purchase
Expert:  Lou P. master tech replied 4 months ago.

Let me check the link

Expert:  Lou P. master tech replied 4 months ago.

The one you showed will not be good enough

Expert:  Lou P. master tech replied 4 months ago.

Also if you really love your car and plan on doing all your own diagnostics you can buy the factory scan tool for 699$

Customer: replied 4 months ago.
Ok I just purchased the unit you specified and it will be here thursday. Please wait for continuation of this support request for further clarification of fault codes.
Customer: replied 4 months ago.
I cannot rate your performance until we see if your recomendation of the diagnostics tool will allow definition of fault code.
Expert:  Lou P. master tech replied 4 months ago.
I understand your stance and respect it. Keep in mind we experts only get paid when rated positively. So please let me know if there is a issue on your end with my info or suggestions. I am very good with Mercedes. Have been a dealer tech for 16 years. Very honest and very good fix rate. So trust that I will get you fixed up one way or the other. Have a good night. Lou.
Expert:  Lou P. master tech replied 4 months ago.
Oh and also looking over the scanner info I think that for the value it seems like it would do very well. This must be very new because I have not seen it in all the years I was suggesting scan tools. So I'm interested to see its operation and I may get one for myself.
Customer: replied 4 months ago.
Thanks Lou, and will pick up this thread next thursday with tool & codes detected. I feel you have the ability to lead me to the problem and will surely rate you as EXCELLENT when we get there. THx
Expert:  Lou P. master tech replied 4 months ago.
Ok. The chat should stay open. Hopefully you will return to me. Also if you do decide to rate me now you are always entitled to a refund in case you decide you are u happy with the service. Have a good week. Hopefully I will hear from you again. Lou
Customer: replied 4 months ago.
this is Arts wife we will make sure all you mentioned above is done.
talk to you soon !
Expert:  Lou P. master tech replied 4 months ago.

well you have a good weekend and week as well Mrs Art :)