Mercedes-Benz Forum banner

1 - 4 of 4 Posts

·
Registered
Joined
·
77 Posts
Discussion Starter #1
During my recent attempts at diagnosis, and previous work, I have searched - and often found multimeter readings at properly functioning sensors and components. Throttle actuator, CPS, CKS, O2, Idle Control, etc. Shouldn't we try and compile these in a reference page. I'll be happy to put anything we collectively have so far in a PDF format - with relative model/year references. I know this doesn't always prove a sensor/component is properly functioning, but it can identify one that has failed. Might save all of us from starting with the usual suspects and just throwing "cheap" part replacements at a problem. They are only cheap if we are replacing bad sensor after all, even if it is a $20 stop lamp switch. Multimeters are $15, easy to use, and dont require component removal. Good place to start with diagnosis.
 

·
Registered
Joined
·
14,926 Posts
Sounds like agood idea.... :thumbsup:
 

·
Outstanding Contributor Always Remembered RIP
Joined
·
6,543 Posts
Only one snag,, one could give a general resistance reading,, thats OK for knowing if the coil (sensor are coils) open circuit or not. Coils are inductive and one short turn cannot be measured, but in a working environment one short circuit turn will make the thing US.

CPS sensors measure near enough 1kΩ when good and open circuit when bad, and it is the changes in temperature that kill them. to test just put them in a cup of very hot water with the Ω meter still attached.

Parking sensors resonate at 22khz and most faults are due to incorrect painting, though some do go open circuit.

One could give a general idea, but one must also allow for the fact that Ω meters use a voltage to measure with, so as they are mainly inductive components a little difference one way or the other should be allowed for
 

·
Registered
Joined
·
77 Posts
Discussion Starter #4
Thanks For Input

I'm just learning the value (and occasional lack thereof) of multimeter testing. I know we have a handful of EE's on the forum, and certainly am not. You do have to see a coil way outside of the range to know it is bad - but it is still valuable.
One of my initial theories with current problem was bad throttle actuator. But running a meter on it showed good and linear voltage change as I manually advanced it. Alldata had a wide range of acceptable values at different positions, but I was still able to rule it out. Would have been nice, actually, to have seen total failure - at least I could have solved the problem. Meters are best for showing a coil that is definitely bad, and I agree that just because it passes a test doesn;t make a component "good" - but it if fails you know where to start.
Found a bad speed sensor this way (actually just covered in dust). Put the left corner up and spun the wheel by hand with ignition on - should see 3V with rev per second. I saw maybe .25V. SAved me a lot of time, and fixed a limp home condition with a wet paper towel.
Put 12V jumper to CPS today - definitely functioning. Again an example where it really would have been better to not hear it move and know it was bad.
 
1 - 4 of 4 Posts
Top