Check engine light - P2096 - Post catalyst fuel trim system too lean

[Brissie_Mick]

Hi all - My car is a 2016 Polo 81 1.2 TSI with about 75K kms and standard annual VW servicing.

I've been getting the above for a couple of months now. Solid check engine light with about 30% worse fuel consumption than usual.

First time I took it for a long highway drive using shorter gears than usual - trying to burn off something in the cat - and reset the code and it went away for a few weeks.
Next time I took out the O2 sensors, cleaned them, cleaned the MAP sensor, and put in a bottle of "Penrite pro series egr and cat clean" and reset the codes but has now come back after about 300kms

Anyone had this issue and rectified longer term? Any tips? Is this the type of thing I would have to go back to VW for or what type of auto trade would be able to give me a fix for this?

Cheers,

MK

[DV52]

Mick: Hi. Given the work that you have already done on this problem - my sense is that maybe it's time to look at the actual lambda sensor itself - being the one after the cat converter because of the error-code (I think).

I'm not sure how much you know about these probes - so forgive my description of the basics if you are aware of this stuff!

I don't have a wiring diagram for this MQB platform Polo - but just to show how these O2 sensors are arranged - below is a picture from the earlier model Polo (which I made for another forum member)


The set-up on your Polo will be very similar to my pic albeit the wire colors and pin-outs will be different.

So, as you can see - the 4 x pin device contains a heater and the cell (called a Nernst-cell) The post cat sensor is not used for measuring - it's purpose is diagnostics. Anyway, I suggest that you grab a multi-meter with good set of test-leads and measure the resistance of the heater terminals.

Assuming this car has a CJZD engine - the pin-out for the lambda sensor should be:

• Pin #1 =Yellow wire- Signal (Nernst cell)
• Pin #2 = Blue wire - Signal earth
• Pin #3 = Black wire - Heater (+ve Volts)
• Pin #4 = Grey/White wire - Heater (ECU controlled earth)

I can't find any definitive material from VW and the factory zirconia sensors are probably Bosch/NTK - but according to HELLA’s technical documentation, heated lambda sensors typically have a low‑resistance heater element. The expected heater resistance (measured cold) should be:

• 5–15 Ω is normal
• >20–25 Ω suggests a failing heater
• Open circuit (∞) = dead heater
• Very low (<3 Ω) = shorted heater

The connector should look like this:
____
| 1 2 |
| 3 4 |
|____|

Don't bother measuring the resistance of the Nernst-cell - you will just get an open circuit (∞) reading which means nothing!!

Don