I recently failed my emissions test due to bad SAI. I put in a new SAI and EGR/Combi and reset the codes, drove for for a few days, checked Readiness. The SAI is passing and in Ready state but the Cat (that was previously fine and Ready - and just replaced 3 years ago) is not. I drove some more and checked again but still not Ready. A week or so ago I cleared the codes again and have been driving it - same deal.

As I said, there aren't any codes for the Cat... it just wont get to Ready state so I can go pass my emissions.

Any ideas or similar circumstances out there? I really appreciate any help or ideas cause short of taking it in and having them tell me I need a new Cat (again), I'm out of them.

Thanks in advance.

2002 A4 1.8T - about 145k miles

 

Cat functionality is determined by a differential in the readings from the primary and secondary O2 sensors. It's possible for O2s to be degraded enough for problems with emissions to occur, without being bad enough to actually fail and set a code. Since your SAP is reading fine, and that's also monitored by the secondary O2, it's possible that the primary is going bad. How's your gas mileage lately? That's also controlled in part by the primary O2.

It could also still be the secondary sensor - different sensitivity is probably used for SAP flow vs car function.

 

Thanks for the reply.

I did check this morning and the O2 sensors were replaced when the Cat was replaced in May 2011. I wouldn't expect them to be bad this soon but maybe it's possible that the bad SAI would contribute to them degrading much faster than usual?

As for the gas mileage, its hard to say. I live in Chicago and drive the car a few times a month and all city driving so it's pretty hard to say if I'm getting optimal mileage based on the complete stop and go driving conditions that I drive in 99% of the time. I would say that I don't feel that the car is as "peppy" as it once was but, again, limited driving kind of stunts my ability to compare one drive to the next.

I almost feel, at this point, my only option is to take it in and have the shop who did my Cat and O2 take a look at it. Was hoping to avoid that but not sure I can any longer.

 

Sometimes there can be seemingly unrelated factors that prevent the catalyst monitor (or others) to run to completion. Not necessarily anything to do with the cat or the sensors. If it was a bad catalyst, the monitor should still run to completion but then fail. Best to have a scan done and look at all the inputs and outputs. May spot something that's not quite right with one of them, and that could prevent the catalyst monitor from running. Example, coolant temp not what the PCM wants to see. Might be too low but not low enough to set a cooling system fault.
That's the short version. To fully explain it all would take way more typing than my fingers can do! lol

 

Thanks for the replies guys. I was actually lucky and the cat finally went to Ready. I checked it one last time on the morning I was about to call and try to get into the mechanic. Don't seem to catch a break with this car often but I did this time.

Thanks again!