Hello All,

I've been having a heck of a time figuring out what is wrong with my car! I've searched all over the forums and I can't find the answer to my questions!

1991 240DL

Check Engine light will not go off, reading code 1-2-1. I have already replaced the MAF, checked intake system for leaks, and tried resetting the codes multiple times to no avail.

The "new" MAF (pick-n-pull) seems to work perfectly, the car idles smooth, with no hesitation on acceleration. I've tried to read the voltages at the MAF (both disconnected and connected reading return voltages) but I'm not sure the correct pins to measure, or what the correct voltages should be. It is one of the 6-pin harnesses, with wires to pins 1-5.

So, what voltages should be read from which pins? Or outside of that, what is going on!?

Thanks to all in advance!

Code 1-2-1, wiring fault to/from AMM:

Are you using the AMM with the part number that ends with -016 (LH 2.4)?
Have you disconnected the battery to clear the codes?

The wires:
brn/blk 1 - ground
grn-yellow 2 - ground via ecu
red-white 3 - output (~3-4 VDC at idle)
white 4 - burn off wire (no voltage until the engine is turned off, for ~10 seconds)
org 5 - 12-14 VDC from relay, during idle

If all the voltages check out and the code doesn't clear, it may be a problem at the ECU connector, the ECU, or a short/open somewhere.