valmor

Hello mates,

I have following problem with my W212 E-class om651 Delphi fuel system 170hp, there is a current fault code:
P009700 Mercedes-Benz Intake Air Temperature Sensor 2 Circuit Low Input I have read the car with star diagnosis.
The code is current in the faulty memory and it is due to problem with intake sensor B17/8. I have already replace the sensor with new one, as far as i know in this engine the sensor wirings goes directly to the front SAM so i have already tested the wirings and they are OK.

Did anybody has the same problem and what would be the solution ?

Thank you for the support !

Sunnyslope48

I hope you replaced the sensor with an OEM sensor, not aftermarket. Our cars are quite sensitive to having precisely the proper sensors. When you say you tested the wirings, does this mean that you tested not only continuity but voltages, grounds, circuit intermittent breaks, etc? To get perfect sensor performance, you need to have a perfect circuit including connectors.

valmor

Yes, I replaced the sensor with OEM, I have tested it on continuity, voltages and grounds. They are completely continuous, but I noticed that it is around 0.2V when I measure between one of the wirings and ground. These days I will try to run a cable directly from front SAM to the sensor to avoid eventually circuit intermittent break somewhere.

It there is other ideas I am open for them

Sunnyslope48

I think you need to determine the correct input voltage into the sensor from a wiring diagram or other source. Without correct input, the output will be skewed. The input for many sensors on American cars is 5V, not at all sure on Mercedes.

For a 3 wire sensor I would expect to see:
1) a constant voltage (maybe 5V) as the input,
2) a low reference (almost 0V) as ground)
3) a signal out to the ECM.

Is this a 3 wire sensor? 2 Wire? or ?? When you measured .2V, which two wries were involved? Does the new sensor produce the same output as the old sensor?

Mud

Just thinking through this - that code is indicating that the ECU is receiving lower than normal threshold value from the IAT within a predetermined period of time.
I think it's a 2 wire sensor? If so I'd expect it to receive a set reference voltage and send a changing resistance voltage back, the ECU is looking at that return voltage and comparing it to programmed values along with other sensor inputs.
Good path to use oem sensor as replacement to ensure correct calibration.
I suspect a short or poor connection in the circuit, especially with that voltage bleed-off to ground. I think you're on the right track to carefully examine wiring and connectors. Even a small amount of resistance can throw things off. Look carefully at pin connections too.
Are you able to probe return voltage or see it in Star to see values?
I don't know if Star can show wiring diagrams but an inexpensive WIS/EPC cd set does. May be of value to you as you seem to be knowledgeable in setting a plan for diagnosis. You'd be able to trace wiring, find all connectors etc. I bought an eBay set for about $15, takes about 64gb on my laptop but a great tool.
Edit - oops I think I followed right on the heels of Sunnyslope advice.

valmor

Yes It is a 2 wire sensor. I have checked the wiring diagrams in WIS, but think there is something wrong because in all of them this sensor goes directly to the engine control unit. In reality this sensor goes directly in the front SAM however I have already measured the wires that goes directly from sensor to the Front SAM and also the wires that goes directly from Front SAM to the Engine control unit. I have tested pin connectors, continuity, voltages, grounds and circuit intermittent breaks and everything is perfect !
In STAR is described that with turn on ignition the voltage value between sensor connectors should be from 4,50V to 5V, but there in 0.02V (No voltage)
I have already run a cable directly from front SAM to the sensor to avoid eventuallycircuit intermittent break somewhere but there is still NO voltage. I am starting to think that the problem is in Engine control unit hardware of software.