I have a feeling this MOT station was being picky for some of this stuff but what could be the cause of this and how would I fix it?

2004 1.2 12v Fabia Estate with 71k miles and a previously flawless MOT history.

Anything which is causing the ECU to switch to the default non closed loop setting, you should start with having the fault codes read with VCDS.

 

They were not being picky, its a fail, the lambda voltage should switch high and low around an average reading of 1.0 volts for Lambda 1.0.

Just now, J.R. said:

Anything which is causing the ECU to switch to the default non closed loop setting, you should start with having the fault codes read with VCDS.

 

They were not being picky, its a fail, the lambda voltage should switch high and low around an average reading of 1.0 volts for Lambda 1.0.

I think they were being picky about the fuel cap o ring and headlights, the lambda sensor issue is understandable because that's tested with equipment that has no bias.

I will give that a shot, i'll need to find someone with the equipment. Could it be some small exhaust blow that's causing it to read so high?

Running extremely lean*, check brake servo vacuum hose and for other air leaks, but yeah, needs a code read too.

 

Is emissions  warning light not on?

 

Approx geographical location?

 

* See later posts.

 

Edited 19 October, 20214 yr by Wino

15 minutes ago, Wino said:

Running extremely lean, check brake servo vacuum hose and for other air leaks, but yeah, needs a code read too.

 

Is emissions  warning light not on?

 

Approx geographical location?

 

No lights on and since all the other emissions are in order it makes me think there's an exhaust leak. Will check those others thank you!:)

South of UK.

It's so far out I even wonder about their machine or operator?

A correctly functioning closed loop lambda system would correct for any lean-ness or richness within correctable limits, I dont think an exhaust leak would put it out that far, an intake leak yes.

 

Before Wino commented I could not remember if the higher value meant richer or weaker than the Stochiometric ratio.

 

I doubt that its gone onto a limited operating strategy through the loss of a sensor input, MAF sensor for example because LOS mapping is always to the rich side of nominal.

 

By far the best way to check a Lambda sensor operation is with an old school analogue moving coil display multimeter, its the only time mine gets used now.

13 hours ago, redrose_45 said:

No lights on and since all the other emissions are in order it makes me think there's an exhaust leak. Will check those others thank you!:)

South of UK.

 

Yeah, I think it must be this, though you'd think that ought to have been picked up as a separate fault.

 

Last night I was thinking in terms of exhaust leak affecting one or other of the wideband pre-cat sensor or 'normal' post-cat one, both of which are very close to the engine. 

But a leak further back - much more likely - could affect lambda as measured at the tailpipe by their machine without there being anything much wrong with how the engine is actually running. 

Flexi section probably prime suspect, or one of the dual-sleeve joining pieces.

Of course, I forgot that they measure at the tailpipe.

 

There is a case to be made for the Lambda reading being measured from the OBD port, do they interrogate for fault codes in the UK MOT test? Lambda value out of limits would definitely generate a high level generic OBDII code.

5 minutes ago, J.R. said:

do they interrogate for fault codes in the UK MOT test

No.