Pre and post cat lambda sensor

[OldOllie94]

Hi
I'm having issues with emissions for MOT and I'm pretty sure it's a lambda sensor issue I just need to know if the pre and post lambda sensors are the same or different?

 

[DE4NO]

They are different. The pre sensor is a heated wideband sensor and is used to control the fuel trims. The post sensor is a basic type and its only job is to check that the cat is functioning.
If the pre sensor is faulty it should throw an EML. Torque GT sell the sensor, it’s a Denso item.

 

[OldOllie94]

They are different. The pre sensor is a heated wideband sensor and is used to control the fuel trims. The post sensor is a basic type and its only job is to check that the cat is functioning.
If the pre sensor is faulty it should throw an EML. Torque GT sell the sensor, it’s a Denso item.

Thank you.
I have no fault codes but I did have to take it to an exhaust garage to get a 400cell tegiwa cat converter and a pre lambda fitted as it failed emissions on MOT.
The exhaust garage said the pre cat sensor wouldn't reach so he swapped them round so they would reach.
I have no error code though but it failed emissions again and am wondering if it's because the sensors were swapped.
My OBd scanner also says I have 0V/ mA to 02S11

 

[DE4NO]

Thank you.
I have no fault codes but I did have to take it to an exhaust garage to get a 400cell tegiwa cat converter and a pre lambda fitted as it failed emissions on MOT.
The exhaust garage said the pre cat sensor wouldn't reach so he swapped them round so they would reach.
I have no error code though but it failed emissions again and am wondering if it's because the sensors were swapped.
My OBd scanner also says I have 0V/ mA to 02S11

If the sensors have been swapped then the pre sensor will be measuring the O2 content post cat as opposed to pre cat. This is obviously not correct and should be installed pre cat to get a correct measurement.
It’s also best to test the emissions with the cat being hot. Take it for a good blast before the emissions check if the garage will allow.

 

[OldOllie94]

Thanks for your help.
I think it is the lambda being swapped that is causing the issue. I have also just added some dipetane and will indeed give it a blast on the motorway when next taking it for MOT.