Hi!

I am newly registered on this forum, but reading for a while. So far I haven't find existing topic with my problem:

OBDeleven data log

Date: 2025-04-17 13:13

    VIN: TMBHC46Y664582931
    Car: Skoda Fabia
    Year: 2006
    Body type: Estate
    Mileage: 168160 KM

---------------------------------------------------------------
01 Engine

    System description: MARELLI 4TV        7450
    Software number: 036906034KE
    Coding: 00071

    Trouble codes:
        P1196 - Bank1, sensor1, heater circuit Electrical malfunction
            static

I have purchased the service manual with wiring diagrams from "easymanuals" (not an ad, I will remove if necessary), which helped to identify the correct wires and perform tests.

I have unplugged the pre cat O2 sensor, the resistance of the heater circuit on "room temperature" was 4,8 ohms (which is normal, spec is 1-5 ohms), performed the test from ECU to the plug, by connecting a small geared motor with 8 ohm resistance (this is what I had on hand, it will serve as a test load or test light, call as You wish). Key On Engine Off: the motor spins up to max rpm, then gradually slows down to approx 10-15% rpm and stays there, which tells me the ECU is doing it's thing, the wiring is intact and has load carrying capacity (I might be wrong). The same happens with engine running.

When I unplug the no.9 fuse in the fuse box, I get new codes for downstream (post cat) O2 sensor, since they are on the same feed circuit, which tells me the ECU is doing right. No other codes present, the pre cat sensor is "offline", the post cat is "online". The pre cat sensor is replaced by the same 5 wire sensor (6 wires o wire loom, 5 wires on pigtail), resistance value is the same for heater circuit, but no change so far. Cables are inspected (without removing the bandage), no signs of burns, fraying, rubbing, corrosion, rodent damage and such present, no sharp bends, everything looks more like original, no "extra equipment" like alarm system or retrofitted navigation added.

The car had previously a cilynder no.1 misfire, which was fixed by replacing the ignition coil, new 3 electrode spark plugs installed (NGK), the car runs smooth, starts smooth, idle is smooth, accelerates as expected, no smell of petrol at exhaust, but might be slightly rich (post cat sensor is at 1 volt), the previous spark plugs had a nice, slightly light brown color on the electrodes, so no lean condition present.

Did anyone had the same or similar issue? I am thinking about maybe something unexpected is interacting with this circuit. I do not want to throw more parts (unnecessarily) on the car, unless I can 100% verify something is bad, so I would really appreciate some suggestions for further tests, to verily "goodness or badness" of certain components.

Thank You in advance!

Best regards

Pali_87

It could be a dirty lamda sensor. If the car had a misfire it could have contaminated it due to unburnt fuel etc. I assume the resistance would be the same if it was dirty or not. Might be worth trying a new one or a known good one.

Hi Alasdair!

Thank You for the response, as You can read in my post, the new lambda probe is already installed. Since day one with the new probe, there is no signal. I assume there is a wiring issue between ecu and probe sensor cables: probe connector pins 1, 2, 4, 6 and 81 pole ecu connector 51, 52, 70, 71 pins. I just need to take a big breath to dive into it (not my favourite freetime activity to measure continuity, but if it has to be done...), so far I have no other clue (or a bad ECU, what I would like to not really just shoot on with the parts cannon...).

My theory is: If there is a broken signal wire from ECU to sensor, there should be more codes (all cannot be broken but not the heater circuit, since it is considered as working), so I would just use more in open loop (no lambda control), since it is not running lean. Maybe I will get at least an intermittent code to start with.

I will keep updated.

Sorry missed bit re neew lamda. Good luck with checking wiring etc.

Alasdair