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Lou P. master tech
Lou P. master tech, Mercedes Technician
Category: Mercedes
Satisfied Customers: 4958
Experience:  15 years master certified 100% fix rate and have access to factory radio codes, wiring, and instructions.
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Getting codes P0720, P0500, and P1747 on 2000 S500 after

Customer Question

Getting codes P0720, P0500, and P1747 on 2000 S500 after accidently going through car wash without covers on the fuse boxes in the engine compartment. The one on driver's side got wet, so I removed switches and relays and dried them out with blow driver. Upon leaving the car wash, the car went into limp mode with limited speed. PROBLEM: Car will not start when I turn the ignition switch. Please help.
JA: Can you turn the steering wheel at all? And what about the key? Is it worn or damaged?
Customer: I can turn the steering wheel with much effort - no power assist which is another issue I noticed on my short ride home from the carwash. The key is in good condition with no apparent problems.
JA: Are you fixing your S500 yourself? What have you tried so far?
Customer: Fixing myself if I can and the problem is not too complicated. I tried disconnecting the negative terminal on the battery to reset things. That did not work.
JA: Anything else you want the mechanic to know before I connect you?
Customer: No.
Submitted: 1 year ago.
Category: Mercedes
Expert:  Lou P. master tech replied 1 year ago.

Hello, my name is***** and i will do my best to assist you.I am going over your story now and will reply back soon with some info,thanks!

Expert:  Lou P. master tech replied 1 year ago.

ok so the bad news is those codes point to a different issue then what is causing the car to not crank. those codes all point to the transmission electrohydraulic control plate. the speed sensor has failed . im guessing that the scanner you are using does not read any other module then the engine module which will not help us.

there are control modules attached to the fuse boxes called the "left front sam" and "right front sam" and they house communication wiring that goes between all the modules. when the communication system gets taken down the car will not crank as the signals are not computing between all the modules. i can tell you that if the modules got wet then they most likely will need replaced. sometimes you can get lucky and clean them out but most times the water shorts out the internals. without the proper scan tool we cannot even know where to begin. in most cases i stay optimistic and try to assist but with one such as this there really is no good way to start diagnosis without knowing what the computers are seeing or not seeing. please LET ME KNOW YOUR THOUGHTS, do not simply rate negative based on the info i stated, that does not change the scenario i know this may not be good news but its the truth, i have been doing this almost 20 years and when issues like this arise they are complicated in person let alone over the internet. i think it should be diagnosed at a dealer since they have the scan tool to do the job. Lou P.