W124 OM602 Ring Gear Speed Sensor
 

I have a W124 OM602.962 and will be running through the “07.1-2006 Testing electronic idle speed control” as a starting step to track down my inoperative tachometer.

On page 5 is says to check for >2.8VAC signal at idle from the ring gear speed sensor but in other sections of the same document it says the minimum signal should be >4VAC.

Which is it? Thanks.

OW- having just diagnosed my OVP problem, it is fresh in my mind (thanks for the support, by the way).

Are there any other functions (A/C inoperable, or ABS light on) that might suggest an OVP problem with your car?

Regarding the tach pickup voltage, I don't have a specific answer, but I suspect that if the pickup is bad you will see Zero volts. My gut says that if you see any voltage at all, it's probably good.

SteveM

All electrical functions work correctly and I just had the Tachomer rebuilt, new capacitors and all.

I do have a 1600 Hz signal at the tachometer connection, which is correct at idle. But what I do not know is if the signal is "weak", or if it is even possible for it to be "weak".

So, I plan to test the source(s) of the signal the best I can.

Anyone?

Have you had a chance to measure the voltage yet?

Steve.

I ran the tests and the VAC output and Resistance readings where within the acceptable limits set by MB. Although I'd like to get a answer to the 2.8VAC and 4.0 VAC limit discrepancy I stated in my original post. You can open the attachment to see what I am talking about.

Speed sensor measurements (per document 07.1-2006)
3.52 VAC at Idle
560 Ohm

When I removed the speed sensor form the EDS input, the idle speed dropped noticeably. When I reattached it the idle speed went up to normal. So it sounds like that part of the circuit working OK.

Does anyone have a W139 OM692.96 that can take a VAC measurement of the tachometer input to the instrument cluster?

Thanks.