Use Rear O2 Inputs For Analog Sensors

Several people removed their rear/post-cat O2 sensors and just left the ECU inputs unused. (Make sure you set c_conf_cat to "1".)

After taking a closer look at those two input in INPA, we see that they are rated for voltages from 0V to 5V with an accuracy of 4.8828125mV.

Why not using those otherwise wasted inputs for something handy like integrating a manifold absolute pressure (MAP) sensor or wideband lambdaprope?

Both, the MS42 and MS43 share the same pinout at connector X60002, which is the second connector from the right looking at the ECU mounted still in car.

As we you see in the schematics, both lambda probes have four connections:

Lambdaprobe	X60002 Bank 1 / 2		Description
Pin 1	-	U_HR	Ignition switched +12V for heater element
Pin 2	Pin 07 / Pin 19	T_LHH1/2	PWMed ground for heater element
Pin 3	Pin 22 / Pin 24	M_LSH1/2	Sensor ground
Pin 4	Pin 16 / Pin 18	A_LSH1/2	Sensor inputvoltage

The minimal setup would be using only the two inputs at pins 16 and 18 and feed a sensor return voltage into them.

But there's also a +12V supply switched by ignition and a ground connection, we can use those for creating +5V to power the MAP sensor by using a LM7805.

Attention: Never use the PWM ground to ground your sensor, as the ECU uses this to control the heater element inside the lambdaprobe!

Also keep in mind, that the signal ground was never rated for high currents like a heater element. Use a seperate, solid ground when you expect a higher load than a few mA like a small 5V sensor usually takes.

The sensors can be read by INPA, RomRaider, TunerPro or any other logging program. Just make sure, that you input the matching formula to convert volts into bar, kpa, psi or lambda, afr.

For most wideband controllers, the conversion from the 0-5v analog output signal to AFR is (voltage x 2) + 10.