Hi guys,

I've had a trouble code throw up on my instrument cluster so I checked the code = P1135 (and U1702). Car is a 1.2 16v mk2 Punto.

I'm a bit confused about the wording though, so hope someone could help me out.

In position 3 Piston; Oxygen Sensor B1-S2; Preheating resistance 1 above catal.; Oxygen Sensor B1-S2.

I am assuming it is Bank 1 Sensor 2 which I guess would be the one after the catalytic converter underneath the car, but why does it say "Preheating resistance 1 above catal"?

Is it just because there is a substantial reading difference between the pre-cat lambda and the post-cat lambda?

Thanks in advance,

P1135 for fiat means you have a problem with o2 sensor after the catalytic converter, or the wiring to that o2 sensor, most likely with the o2 sensor heating element or circuit for heating element.
If you have a multi meter and o2 sensor has 4 wires 2 of which are white wires, Unplug the sensor and measure the resistance between the white wires connected to o2 sensor, if open circuit you need new o2 sensor.

If you are reading live data from pre and post catalyst o2 sensors there should be a big difference once the ecu goes into closed loop operation, thats when it's up to normal operating temperature

Thank for that!

I just read the resistance of the white wires of both sensors at about 8.9 (sometimes little more probably due to me wiggling the pins), so I believe the preheater elements are doing fine. So I assume it was just a one-off trouble code, I cleared the codes, so I’ll have to see if it comes back throughout the day.