I followed the instructions below and when I got to 046 I received the NO OK. Is that a definative BAD CATALYTIC CONVERTER? No chance of the sensor being bad (it passed block 36)?
So, here we go. Car is at operating temperature. And I will assume that you're at least somewhat knowledgeable about the use of the Vag-Com.
1) clear codes
2) reset throttle adaptation (04/060)
3) start engine and let it idle
4) 04/030 and check o2 sensor control. you want to see 111 in field 1 and 110 in field 2
5) 04/107, and click start test. wait until field 4 goes from test off to test on to syst. ok
6) leave basic settings, crack throttle open briefly so RPMs go over 3k
7) back into basic settings, enter 034, start test, press foot on brake while flooring throttle. RPM's will increase to about 2300. Test will begin soon after exhaust gas temperature passes 350 degrees. Test will run, and you should see B1S1 OK.
8) now go to basic setting group 036, start test, at idle, and see if the rear sensor tests ok. you should see B1S2 OK.
9) repeat step 8 in setting group 037
10) group 043, start test, brake and throttle together again, and run test until you see B1S2 OK.
11) and now for the litmus test. go to group 046, brake and throttle together, and run the test. test likely won't start until exhaust gas temp goes over 550.
If everything checks out except for step 11 above, rest assured that you have a bad cat. I know it looks like a pain in the ***, but all of these tests together literally take about 5-10 minutes to perform.
So I changed the cat and sensors with a good used OEM cat and I still have the P0420. I also had a P0441 for the Evap system, so I changed the N80 valve and that went away.
What else can it be? Background: 04 Passat 1.8T that was bought with a blown motor. Installed a low mileage (city) 03 engine. Had P0420 since I started driving car.
Seller of the cat said I need to try driving it with 2 tanks of Premium gas (I only run 87 octane...in all 3 1.8Ts that I've owned) and I should have used the 03 ECU and sensors.
I'm at a loss. I'll try the premium gas, but the car is for my daughter and I don't know if she will run it on premium once she starts pumping gas (paying too). LOL
A P0420 is often a bad CAT, sometimes an O2 sensor, occasionally an exhaust leak, and sometimes the engine isn't running well and puts too much crap in the exhaust. When my CAT was going, I could get the light off for a bit by using Shell 93 octane and a bottle of Techron. Personally, I think your "new" CAT is borderline at best - especially since the seller already knows how to coax it.
Expect to be toasted a bit by the members by running 87 octane fuel. It's certainly contributing to your problems.
Check for exhaust leaks, many times the exhaust clamp tends to leak once reinstalled. Also carefully inspect the flex joint. I think all 1.8t B5s and B5.5s use the same post cat sensor. How many miles on the replacement cat? It is reasonable to replace a cat after 10+ years, so I wouldn't be surprised if that cat is at the end of its road.
Not to cast aspersions on a member, but there's a reason it's illegal to sell used catalytic converters, and it's not just to cut into the theft of them. It's consumer protection; very difficult to tell if it's any good before you install it.
I spoke to the seller and he assures me that the CAT had no codes before he pulled it. He seems like a very reputable person.
He said it could be an exhaust leak or it needs a fuel system cleaning. I installed a new gasket at both ends of the CAT and the flex joint appears to NOT be leaking but the mesh is broken at one end. Also the middle box has been removed from the exhaust system.
I'm going to try running it on premium gas and my son wants to Sea-Foam it.
The car is designed to run safely, if not optimally, on (ugh!) regular unleaded. That includes not throwing codes. Even if correct fuel temporarily puts the light off, like it did mine, you still have a problem.
If the rear sensor is good, the exhaust isn't leaking, the engine is running at the proper mixture and temperature, and not leaking oil internally... there's not much left but the CAT.
I had a P0421, the other side. It was neither the cat or o2 sensor....at least so far. I cleaned the MAF, replaced spark plugs and wires, new air filter. No code in 400 miles. Make sure these are good before throwing parts at it.
I ran two tanks of premium fuel through the car and the code has not returned. It's weird, but it did. I was monitoring the CAT temp (and comparing to my wife's B5), and the CAT temp was lower by 80 degrees, but by running the premium the CAT temp came up about 50 degrees.
Also, a used post cat sensor will make the cat appear "better". If you replaced it and the previous owner had a slow, marginal "good" one, this could tip the balance to show it bad.
BTW, you can buy very cheap aftermarket cats with very good performance. I used to be against aftermarket cats around 7-8 years a go, but that has changed in the last 4-5 years (my opinion and probably the quality of the cats).
With a normal OBD 2 scanner, you look at the Long Term Fuel Trim (LTFT). You can also check Freeze frame when the DTC was stored and see what were the conditions when the code was set (including fuel trims). I forgot now which one is LTFT in VCDS, maybe 34? I could be wrong, but this is the first number that came to mind.
You can also use Short term fuel trim (which is the instant fuel trim).
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Related Threads
?
?
?
?
?
Volkswagen Passat Forum
3M posts
158.6K members
Since 2002
Passatworld is a forum community dedicated to Volkswagen Passat owners and enthusiasts. Come join the discussion about mods, Quattro, Turbo Diesel, reviews and more!