X11 Port Reading Correct?
 

Hello,

Just took the following readings from the X11 Diagnostic Port on my '90 300E:

Key on
Positive lead to pin 3
Neg to ground.
Reading: 81.36

Engine on but not warmed up.
Positive lead to pin 3
Neg to ground.
Reading: 81.36

No fluctuation at all when the car was warming up.The only time I get fluctuation is when the meter was not grounded. At that time the readings were in the 98 to 110 range. I suspect that is not an issue though I could be wrong.

According to the manual, 80% indicates a fault in the intake air temp sensor. My guess is that my reading is close enough to warrant replacement of the sensor.

Also, when using the Craftsman multimeter recommended by Larry Bible, I get some strange readings at the X11/4 port pin 3 when reading pulse codes. I believe I got a 5.xx reading once but it fluctuated badly. Seems to me that I am doing something wrong. Key on and I ground for 2 to 4 seconds. Do I lift off the ground at that point or wait for the first reading to appear?

BTW: This is a great little meter.

Any thoughts?

chicago124

Well, you are right about the fault code.
The intriguing part is the ignition on engine off reading.
If you have a Cali. car it should be 85% (according to the manual). Otherwise 70%.
Engine running but cold should be 50%, and then oscillate after warm. (unless a fault, of course)
The sensor might be good, and there could be a wire problem. (I always check the wires first).

My 2 cents.

Hi,

Car is a federal car bought in Illinois.

From what I gather, the sensor itself is in the air intake hose before the air cleaner box. (Correct?)

If so, I am going to pull it and do a little checking with the multimeter before replacing it.

As for the wires, I'll have a look and see what I find.

Thanks.

chicago124

"From what I gather, the sensor itself is in the air intake hose before the air cleaner box. (Correct?) "

It depends on the year and model.
Try to include them in your signature for clarity. It simplifies things for people when trying to help. ;)

Hi,

Sorry about that. It was in the initial post - '90 300E

Thanks,

chicago124 -- 1990 300E 134K miles

OOOps, my bad.
Still a good idea to have it on the signature.
There is a great posting right now. MAS replacement, I believe is your same car. Illustrated with a diagram.