Why does OBD scan work like this?

Page may contain affiliate links. Please see terms for details.

sceh

Active Member
Joined
Jul 31, 2015
Messages
225
Car
w123 240TD
If you have a computer it scans at startup for faults and if it has a fault and you replace the part it works OK.
So why does the OBD scan work differently? If you have a fault and repair it the warning light will still be lit until the code memory is cleared.
This makes no sense to a computer person like me so why does it make sense to MB? Love to know..
Any ideas?
 
Because you can't crash your laptop at 70mph and kill yourself and others.

Cars have to maintain the safest possible situation, and it's safer to assume the fault is still present until a qualified person has repaired it and cleared the fault code, than to just assume on next start up that since it's not yet detected the fault again, that it must be now fixed.

With a computer, the goal is always to get up and running if it can. So unless the faulty memory module is still preventing it from booting successfully, it'll boot. Cars can't test every component on start up, some problems only present themselves after a certain collection of circumstances arise.
 
Last edited:
Not all faults need to be cleared for the lamp to go out. It depends on the fault and usually if the lamp doesn't go out it's because the replacement part needs some sort of setting-up or coding to operate correctly.
 
Not all faults need to be cleared for the lamp to go out.

In addition to this, some will clear themselves after several starts, when the car can be sure the problem hasn't reoccured or has gone away.

The airbag lights for instance, if you connect the battery back up to the car with an airbag disconnected, you'll instantly trigger a fault code. If you disconnect the battery, reconnect the airbag, and connect the battery again, you'll get that sinking feeling as the SRS warning light is still lit up, but several starts/stops later it'll go out as the car has consistently heard "OK" messages from the SRS systems since.
 
just like my aircon light flashing even after a regas , the system has to be told by a human that its now ok to run again after a regas , to protect the compressor from low oil which is contained in the aircon gas.
 
My wife operates on the same principal as OBD. Once she has detected a fault, she will commit it to Random Access Memory. At a time and place of her choosing, she will recall the fault and commit it to speech. Certain faults will see her refuse to operate or function as expected, rendering her useless, apart from being pretty to look at. Some faults can be very costly to rectify and require several visits to my wallet. Once cleared, they are still stored, waiting dormant on the opportunity to be recalled an used against me.

Some faults can cause long term damage. I list these for information:

Looking at other women's breasts in the supermarket. This can be terminal and require major surgery.
Mentioning her best friend looks very pretty. As above - Can be fatal.
Mentioning her best friends name during lovemaking - Terminal.
 
Last edited:
Mine's just the same, Bruce. But OCD not OBD :) :)
 

Users who are viewing this thread

Back
Top Bottom