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Error Code P1153 is defined as Heated Oxygen Sensor (HO2S) Insufficient Switching Bank 2 Sensor 1. This means the HO2S didn't switch enough times. This code is a generic trouble code, meaning it applies to all vehicles equipped with OBD-II system, particularly those made from 1996 up to present.

Quick google reveals all ;)
 

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Looking at the code list, P1153 states "bank 2 fuel control shifted lean".
That means an anomaly with the data for precat O2 sensor for bank 2. I'm unsure which is bank 1 and bank 2 but disconnecting one of the precat O2 sensor would introduce another code to be able to identify which is which.

Have a look at live data for both precat O2 sensors. It may be better to stream both as graph to be able to look at the voltage wave form. If there is a significant difference that may suggest it is the O2 sensor.

What to look for is a slow response from the sensor. It may be it spends more time at high or low voltage or have a wide U shaped peak or trough rather than a sharp V. It may go from high to low and back slower than I Hertz (have less peaks and troughs in same timescale). The median voltage is 0.45 bolts for a standard Zirconia sensor.

It could be the sensor but there are other things which could affect it. As it reports weak, it probably isn't a spark plug or coil. You didn't report a misfire. It could be an inlet manifold leak which allows slightly more air in but you didn't say anything about an irregular idle or specific conditions when the code is likely to be triggered. You mentions it seems to be random. It could be an exhaust manifold leak also which allows air to be drawn in and affects the sensor reading.

What you stated (and didn't state) makes me think it is the O2 sensor itself. They do degrade with age and distance and have a design life of 100k miles. They may function well for less or far more than that though.

Hopefully it is just an O2 sensor.
 

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Discussion Starter #4
Thanks both for your replys.

Yep, no obvious misfire, dodgy idle or exhaust or inlet leak, car seems to run perfectly fine.
Its about 96k too, so maybe an idle time to replace both pre cat lambdas, its off to germany in a few weeks for a 2k miles road trip.

Thanks in advance

Matt
 
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