Hi,

Having problems to pass MOT with a Mk1 S40 2002 with 1.6 litre big block gasoline engine.
Lambda sensor has been replaced by the previous owner not more than a year ago, it's a Ready-fit Bosch with the original connector on the wiring.
The car is showing P0135 fault code which is for the heating circuit malfunction in the Bank1 Sensor1, before the cat.
However I think the O2 sendor is good, the sensor has been replaced by the previous owner not more than a year ago, it's a Ready-fit Bosch with the original connector on the wiring. Reading the resistance between red and white wire on the sensor gives around 4.5-6 Ohms which seems to be within the OK range and gives the information the heating element is intact.

Pulled out the connector and read contuinity between the pins and chassis ground and voltage reading with a multimeter gave this information:



Is there something odd on these readings? To me, the engine running and reading between red-black and green-white wire being 9,4V seems abnormal, shouldn't it be +12V? Also, the green-white wire gives a 3,65/3,66V reading with the key in ON position. (Think the red-black should be the positive voltage for the heater element and green-white is the ground, connected into ECU)
I think the system is equipped with the EMS2000 engine control by the wiring colors, however the O2 sensors are located beneath the seats so that would indicate to Melco 1/2, but with that the wiring colors doesn't match. I've used vccn.no supplied wiring schematics for the research.

Also, with the key not in place and ignition off, the red-black and white-black wires gives beeping with the contuinity check with ground on the multimeter. The same happens with the ignion ON.
While engine is running, only the white-black wire beeps on contuinity check with chassis ground.


Electrical problems ain't something I understand so anybody with more knowledge and suggests on how to move forward with the issue?

 

A couple thoughts

1) the wiring/connector is corroded or damaged. Did you do your measurements from the firewall connector and inspect wiring to the sensor?
2) Did the prior owner use the correct part#? I believe the turbo engines use a Bosch management system but read somewhere that the NA's use Denso for some model years. You may want to double check the correct OEM part for your model.
3) you may have some other intake air leak issues triggering the fault code

 

The connector and pins seems to be in OK condition. They are located underneath the dash/radio inside the cabin.
The part is correct so to believe. It is a natural aspirated powermachine
Air intake leaks I've tried to check with brake cleaner but no luck on that, my thoughts at this point is the problem may lie within the wiring and voltages because of the several irrational readings?