I recently got a pending DTC code P0100, which is the malfunction of the MAS. I had my MAS replaced almost 1 year ago by a Mercedes Dealer under warranty.

Since this is a pending code, it did not light up the MIL. However I have concern for it.

I have a tech CD, and I went though some of the diagnostic. However I want to verify with a Mercedes Mechanic to make sure the tech CD I have isn't wrong.

The tech CD suggested to test the voltage supply by using the ECM wire 48E against the MAS wiring hardness pin #4 and #2 with Ignition ON. The tech CD shows 48E as the MAS Ground, and the MAS wiring hardness pin #4 as 5v supply and #2 as 12v supply.

The voltage I get for #4 is .9v and #2 as 2.4v. HOWEVER, if I connect the voltage meter's ground to the car's common ground I get #4 = 4.99v and #2 = 11.98v

So I don't know if this part of the test was wrong by the tech CD.

The second test is to test the ground wire on the MAS connector. Using 46E and MAS wiring hardness #3. The test should show 5v, and it does.

The next test I did was to make sure all the wires from the ECM loom isn't shorting out. So I test for continuity from wire 45E-48E against MAS wiring hardness 1-5. This test also show up fine, at least no resistance.

The final test I did was on ECM 47E and 48E. This tests the voltage from the MAS sensor, 47E = MAS Signal, and 48E = MAS Ground. Tech CD suggested with ONLY Ignition ON it would be around .9v-1.1v. However I am only getting .1v, and while at Idle, with ECT temp at 70+ it should be in the 1.3-1.7v, my reading was .24v.

I want to make sure the Tech CD is publishing the correct voltage, because this does indicate a bad MAS, but with this low voltage I suspect the car would not even idle or run.

I really like to find out about the voltage test. Because it also mean it can be my ECM. But I would imagine the MIL would light up.

Anyone with any knowledge of this, please advice. I greatly appreciate it. If there are any additional test I should do, please let me know.

thanks!