jcman

You can't or shouldn't ignore this advice that was mentioned before,
"Your best way to diagnose is to use vagcom to see real time values and pending codes that are not latching but resident."

Those codes can also be from leaking flex pipes and the list goes on so do your detective work and then come back and report the findings.

4Driver4 is spot on with the CTS if it has not been changed, I'd take his advice too.

4Driver4

In reading your post, I thought you were content to live with the cat codes but were concerned about poor mileage.

Cat codes are they because the car "needs" cats...according to the crappy programming in the ecu anyway.

Poor fuel economy and cat codes are unrelated.

ajg617

Are there any symptoms of a 'bad' CTS? Can a partially plugged heater core impact the CTS readings? Some loss in heat, performance, and fuel economy this winter.

kappa4201

Yes sorry to blend the issues but if the cats are ok and won't cause any further damage I am alright with the CEL on. I wasn't sure if poor econ/ foamy oil was a cause/symptom.

I just got in touch with a guy who is going to vagcom my car Thursday.

Is there specific tests that should be done? Sorry I'm not familiar with the software or procedure.

Airbag

in simple terms - the CTS is one of the highest failing parts of our cars , and yet one of the cheapest to replace . i would consider it a maintanance item for every 5 years just to keep it from annoying me.

The CTS will monitor the coolant temp .. it richens the mixture when the car is cold and leans it out as the senses the coolant warm up . depending how it goes bad it can dump fuel in constantly thinking the car is cold. therefore bad fuel consumption and cooked cats.

ddillenger

I just want to state for the record, that there is post cat lambda control, and bad cats can in fact cause bad fuel trims.

jcman

Here is the fact about your statement right out of this link: https://www.audiworld.com/forums/sho....php?t=2580765

Quote>

So, now that we know that the ECU wants to be able to control the A/F ratio. It has a prescribed set of values (maps) for a given RPM, Load, etc. So, the ECU tells the injectors to pulse for exactly XX.X milliseconds and that SHOULD get us the proper A/F ratio that we want. Well, if you tell an employee to go do something, you want to make sure they actually did it, right? The ECU has some snitches (the front O2 sensor and the MAF, for the most part) that will report back whether or not the desired mixture has been attained. The rear O2 sensor is used mostly to monitor the condition of the catalytic convertor, although in some applications it also contributes to trim information.

Prospeeder

This is not always true. Converters can melt down, break apart, and be damaged and restrict the exhaust. This will absolutely drag mileage and power down. With the high coil failures seen on 3.0s It doesnt surprise me when I see the fault lights on. All it takes is a few missfires and that cat is super hot, raw fuel hits it and bam overheat meltdown.

We of course dont know if the OPs are that way but removal and inspection would make it clear. It may be like the 2.8's in A6's and the logic to set the code is too sensitive. Set of oxygen sensor spacers seem to trick them pretty good.

ddillenger

It appears as though you are disagreeing with me? I am stating, for a fact, that there is post catalyst lambda control on his 3.0.

I can happily show you in the factory calibration if you'd like.

jcman

You should quote me but I get who the post is directed to.

If you are referring to the
Bosch LSU 4.7 Broadband Planar technology I don't believe it was used on any C5, we do in fact use the (new design at that time) LSU pre-cat sensor and the LSF post-cat sensor system that go back to the Motronic M5.4.2 that Yes suggest the post sensing does play a role in the "Long Term" fuel trim information not "Short Term Directive" considering that no related DTC's exist.

So here is my question:
Why would any engine management system allow more fuel enrichment
under a known cat performance DTC issue leading to more damage?

I'll sign that class action lawsuit all day long!