# Sensor signal out logging

I am trying to reverse engineer a pressure sensor thats connected to an ECM and outputs pressure ratings in bars.

i want to tap into the sensor with arduino and create my own voltage --> bars data.

This is the sensor wiring diagram, the sensor is "G31"

from my research, i am concluding that pin 3 is the Ref voltage from ECM, which is tied into another sensor (idk why). pin 1 is ground and pin 4 is signal.

i tested all 3 pins WRT to a known ground, while disconnected from the sensor but connected to ECM and power on.

pin 1: 0v

pin 2: does not exsist.

pin 3: 5.5v (ref)

pin 4: 4.95v (signal).

when i logged pin 4 voltage WRT to ground, and callaborated that data to the known pressure, i got a graph that does not represent any function, it was literally a square blob of data.

2 possibilities for this:

1: Pin 1 (ground) floats, need to tap into ECM ground.

2: Reference voltage changes, need to log voltage drop WRT to ref.

do those 2 options make sense, and which would be most likely?

• it is unclear what you are asking ...... there is no question in your post, other that thoughts? – jsotola Mar 10 '19 at 21:04
• are you able to plot the voltages on pin 3 and on pin 4 relative to time? – jsotola Mar 10 '19 at 21:08

Have you read the service manual? Is your concept valid for the sensor interface?

(just a long comment)

Bosch Sensors have a thermal offset Temperature coefficient offset (+25°…+40°C @900hPa) 1.5 Pa/K, equiv. to 12.6 cm/K

Thus as the engine warms up you may see a hystereis noising effect of your linear data, so there is no correlation when all lumped together

e.g. BMW, VW 97

When the intake manifold pressure is low (high
vacuum) sensor voltage output is 0.25-1.8 volts at the
ECM.
When the intake manifold pressure is high due
to turbo boost, the sensor voltage output is 2.0-4.7 volts.
The sensor receives a 5-volt reference from the
ECM.
Sensor ground is also provided by the ECM.
The ECM uses boost pressure combined with the intake
air temperature to determine the volume of air entering the engine

DIAGNOSIS AND TESTING - BOOST PRESSURE SENSOR
If the boost pressure sensor fails, the ECM records
a DTC into memory and continues to operate the
engine in one of the three limp-in modes.
When the ECM is operating in this mode, a loss of power will
be present, as if the turbocharger was not operating.
The best method for diagnosing faults with the boost
pressure sensor is with the DRB III scan tool.