Technical Emissions and lambda sensors etc

[Elxpunto90]

I put car in for mot and it has failed on emissions O2 is high I ran a diagnostics on car and was coming up with ( catalyst system efficiency below threshold bank 1 ) whilst on diagnostics I ran a test on bank 1 and bank 2 O2 sensors whilst car was running and came up with voltage and readings on one sensor and no voltage but readings on the other sensor. the top lambda on my Punto 1.2 60 is reading nicely but the lower co sensor isn't reading nothing swapped top and bottom leads on sensors and still no reading on it I presume it is the lambda sensor that has packed up it also feels like it is misfiring slightly any ideas please oltag

 

[Ziggy122]

The picture you attached i couldnt be arsed to make head or tails of it tbh

Anyway since Pre and post lambda's are the same type - you can swap them over yes no problems

IF say the Post cat (after cat) sensor is flatlined
You swap pre and post over
The Pre then flatlines its pretty dam fire sure the sensor is dead
But make wiring for the sensor isn't at fault here

Avoid cheap white boxed sensors - as they often work fine for a short while then fail / dont work at all

Get a quality NGK/Bosch or OE sensor of a scrap vehicle



Ziggy

 

[fingers99]

Swapping leads isn't going to accomplish the same as swapping the sensors.

Still, if there is a misfire, it'll not help with emissions at all. In my experience, cars with misfires fail.

The second sensor only checks if the fist one (and the cat) is working. Has no effect on emissions.

I'm guessing you mean CO2 (carbon dioxide) for 02 (oxygen)?

 

[Ziggy122]

Swapping leads isn't going to accomplish the same as swapping the sensors.

Still, if there is a misfire, it'll not help with emissions at all. In my experience, cars with misfires fail.

The second sensor only checks if the fist one (and the cat) is working. Has no effect on emissions.

I'm guessing you mean CO2 (carbon dioxide) for 02 (oxygen)?

who said misfire?

Ziggy

 

[fingers99]

who said misfire?

Ziggy

".........it also feels like it is misfiring slightly any ideas please." the OP, at the bottom.

 

[PuntoHowTo]

If you have 0volts then it's likely the sensor or wiring has become short circuited, swapping the sensors as ziggy suggests will tell you of the fault is wiring or the sensor, of the fault moves with the swap it's the sensor, if you still have the same orientation of voltage and no voltage then there's a short somewhere in the wiring.

If it's the sensor, change the sensor not quite sure what more can be said?

As fingers points out if the issue is pre cat then the ecu will be running open loop and the engine is likely to run rough and miss fire change the faulty sensor and it should sort all issues
If the post cat O2 sensor is faulty it the ecu will run closed and fuel properly but you'll still see an engine warning for emissions reasons, I seem to think you should see lower voltages post cat as the catalysed gases increase the amount of free oxygen ions and oxygen decreases the output of the sensor

In any case you could swap the sensors over like fingers suggests to prevent misfiring issues while you wait to fit a replacement

 

[atom0007]

if the issue is pre cat then the ecu will be running open loop and the engine is likely to run rough and miss fire

I don't think that's right - the engine runs open loop when it's cold before it goes closed loop, and doesn't misfire.


I would expect rougher running and lower efficiency for sure, but not misfiring

 

[Ziggy122]

".........it also feels like it is misfiring slightly any ideas please." the OP, at the bottom.

FML :bang:

I don't think that's right - the engine runs open loop when it's cold before it goes closed loop, and doesn't misfire.


I would expect rougher running and lower efficiency for sure, but not misfiring

Yes on cold start - its Open
Once warmed up its on closed
Only thing i can think of to make it miss is either ECT is lying BADLY
or the ignition systems dying too

Ziggy