S40 -02 issue with O2 sensor/wiring? P0135 DTC

[v0lv0mies]

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Lambda sensor has been replaced by the previous owner not more than a year ago, it's a Ready-fit Bosch with the original connector on the wiring.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However I think the O2 sendor is good, the sensor has been replaced by the previous owner not more than a year ago, it's a Ready-fit Bosch with the original connector on the wiring.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?

[fastneutron26]

I have exactly the same problem with the same car and engine option. Did you manage to find a solution?

[Vova585]

1. Find correct wiring diagram(figure out how the system works. What turns the element. Is it negatively controlled(ecm supplies "-") or posititively controlled(ecm turns on "+").
2. Identify wires responsible for 02 heater element.
3. Disconnect connector for 02 sensor
4. Verify which wires are ground and power for heater circut.
5. Forget multimeter or continuity testing.
6. Find yourself 4amp bulb and make a tester light put of it(attach 2 wires and small needle probes to the end of wire.
7. Verify your test light work
8. Start the car
9. Test ground side"-" of heater with 1 wire of your test light at battery 12v"+" and other gently front probing corresponding wire at the connector. (no light, dim light-failed wire, so look for break or corrosion. ) if passed, move to step 10
10. After verification that ground side is intact you can use it as your "-" terminal for testing. Front probe between negative and positive. If you have bright light-wiring at connector is intact, so inspect sensor/replace with oem. If you have no light-broken wire.