jwass

I have an 2000 A8L with CEL light on. It is showing codes 17538, 17536- add. system lean 17545, 17536 -mult. system rich. My mechanic has changed both O2 sensors,2 control modules, and air intake gaskets w/o success. Now says coolant temp sensor is indacting a 50 degree diff between both banks needs to be replaced. Says MAF is ok. I ran car w Vagcom 5800 RPM in 2nd gear Group 002 showed 122g/s airflow whats up? if I unplug MAF will car run w/o codes above if MAF is bad?

PaulW

1. Check fuel pressure. Was this completed?

2. Check air mass sensor. There is a procedure in the Bently to do this at idle. Was this completed?

3. Check O2 sensor before cat and check 02 sensors after cat, also a procedure very detailed in the Bently...was this completed on the two 02 sensors not replaced?

4. Check EVAP canister valve 1. Was that completed?

5. Check fuel injectors. Was that completed?

I don't know how to answer your question regarding airflow, but I bet skiwi does.

Regarding your mechanic, it doesn't appear that he knows what he is doing. Replaced two control modules? What two are they? Plus two 02 sensors....sounds very expensive. And the problem is not solved yet. He needs better troubleshooting skills.

Now he is recommending replacing the coolant temperature sensor? What makes him think that they are actually reading wrong?

Unless he could prove to me that they were the problem, I would not go ahead with the repair.

There presently is an Audi campaign to replace defective MAF's on some 5 valve engines, I believe yours is one of them.<ul><li><a href="https://forums.audiworld.com/a8/msgs/48757.phtml">Another similiar thread, search for your fault codes, there is a bunch</a></li></ul>

PaulW

<ul><li><a href="https://forums.audiworld.com/a6/msgs/320013.phtml">https://forums.audiworld.com/a6/msgs/320013.phtml</a</li></ul>

jwass

MAF at idle was ok. The test at the bottom URL linked is why I think MAF is bad. I got 122 g/s vs 240 expected at 5800 rpm.<ul><li><a href="https://forums.audiworld.com/vag/msgs/456.phtml">https://forums.audiworld.com/vag/msgs/456.phtml</a</li></ul>

cwatters

I had intermitent CEL with the codes for small EVAP leak and Bank 1, Bank 2 too lean. I don't rember the code numbers, but if you do a search I posted them in this forum. Long story short, replaced a hose at first and it worked for a day. Dealer then replaced MAF under warranty (7/70,000) and no CEL light for a couple of days now. Others have indicated that the MAF is the only thing that fixed the problem. Do a search here and then go back with the results. That's what I did.

skiwi

most likely maf. swap with a known good, but the flow rates are clearly suspect. use vag-com to graph a wot run with the maf flow and it should be clear. paul or myself could supply our flow rates for comparison.

also agree with paul that your mechanic has left his brains in the toolbox.

jwass

Dave,
thanks for the help. But what is a wot run?
Bad news is car has 73,000 mi, good news is I have an extended warentee.

Jay

gondar

My 2000 A8 was flowing more air than yours (about 220 g/sec) at top revs and the MAF was bad. I kept tripping lean codes. The car was obviously pumping more air than the sensor was reading. Your reading impresses me as very very low. Have the MAF replaced under the program. VW/Audi need to stop purchasing faulty vital components such as coil packs and MAF sensors. They must be squeezing their suppliers hard and reliability is sacrificed.

gondar

WOT= wide open throttle, i.e., max airflow

skiwi

what i mean by a wot run is:
1) plugin vag-com
2) record group 0/3 (all 4 blocks). while you are there do group 4 &amp; 5 as well.
3) with engine @normal temp run to red-line

have a look at the csv file, and feed it to vag-chart. any glitches should be pretty easy to see.