O2 Sensors - 993

[earossi]

As you may know, there are (4) O2 sensors on the 993 3.6 motor. There are (2) on the lnlet to the cat and (2) on the exit from the cat. My question is does it make any difference on the hook up of the sensors. For example, if I were to change the hookups for the two inlet sensors, will it make a difference to the ECU for the engine? They are not coded, so it is possible to hook them up incorrectly. Just wondering. Same goes for the downstream sensors.

[Bill Verburg]

Originally Posted by earossi

As you may know, there are (4) O2 sensors on the 993 3.6 motor. There are (2) on the lnlet to the cat and (2) on the exit from the cat. My question is does it make any difference on the hook up of the sensors. For example, if I were to change the hookups for the two inlet sensors, will it make a difference to the ECU for the engine? They are not coded, so it is possible to hook them up incorrectly. Just wondering. Same goes for the downstream sensors.

Only on '96 up US and tt, these all run Motronic M5.2 and yes it makes a difference.

These are all OBD2 compliant cars and part of the spec is to measure both pre and post cat O levels in the exhaust gasses in an effort to comply w/ the more stringent '96 US emission regs.

The algorithim employed is to measure the pre and post cat o sensor votage and divide to obtain the ratio, also taking into account the delay in response due to the time it takes the gas to transit the system and also load and rpm variation.


Once the spec limit is passed a CEL is triggered. Additionally aged or contaminated O sensors will also cause the spec limit to be exceeded and will also trigger a CEl.

So wire them up correctly and then only install the upstream ones into the pipes, insulate and isolate the down stream ones and all will be good for a long time.

A better solution is to replace the M5.2 system w/ either M2.1 or an aftermarket solution
the upstream 1-3 use
0.5 Br
0.5 Wt signal to DME pin 19
1.5 Br (heat)
1.5 Re/Wt (heat)

the upstream 4-6 use
0.5 Br
0.5 Wt signal to DME pin 18
1.5 Br (heat)
1.5 Re/Wt (heat)

the downstream 1-3
0.5 Br
0.5 Wt signal to DME pin 77
1.5 BR/Ye (heat)
1.5 Re/Wt (heat)


the downstream 4-6
0.5 Br
0.5 Wt signal to DME pin 76
1.5 BR/Ye (heat)
1.5 Re/Wt (heat)