Hi.

My car was idling at the trafic lights when the RPMs stumbled for a split second then returned to normal. Very soon after that the check engine light came on. I downloaded the code , which was "P1193 O2 Sensor Heater Circuit Open - Infered Fault".

Looking at previous post's this is the downstream sensors, but which one? I am asuming that the X300 North american market cars have 2 front (Upstream), and 2 rear (Downstream).

This also hapened a few weeks bck with the same code, and I cleared it to see if it would come back.

Am I correct that it is the Downstream sensors

The car is otherwise running great.

Any help would be appreciated.

Cheers

Ian

 

P1193 is BOTH DOWNSTREAM SENSORS heater circuit fault (open circuit)

 

Hi.

So both failed at the same time? Seems a bit strange.

Thanks for the DTC it is excellent info.

 

The code doesn't mean both O2 sensors have failed. It doesn't mean any of the O2 sensors have failed. DTCs can only provide you with a symptom not a root cause.

The Downstream O2 sensors share an output for the heater from the ECU. What the code is saying is that there is a high resistance on that circuit. That could be a sensor fault or a wiring fault or a dirty/corroded plug etc on either or both sensors. You will need to investigate to find the actual cause.

Check the wiring circuits and test the resistance of the sensors individually.

 

Also worth checking the fuel trims on both banks as that can point to which sensor is playing up.

 

Hi Cafcpete.
Thanks for your reply

How do I check the fuel trims?

Regards

Ian

 

You need an ODB scanner that can display live data. I use one called BlueDriver connected to my smartphone, but there are much cheaper ones around.
https://www.bluedriver.com