1.4 AUA MOT Saga - high CO, persistent P0135 Fault Code, even after Lambda swap

X

X495

Member
Hi All
I am having a saga getting our 2000 1.4 AUA (Po) through the MOT. A few jobs fixed but currently stuck with high CO reading, MIL and P0135 fault code. Front lambda replaced with brand new (Bosch however rather than NTK). P0135 now triggers immediately and persistently (it was sporadic with the original sensor). Auto elec suggests the new sensor is faulty.
Do I bit the bullet for a new NTK one? I am wondering if I have two underlying problems though, and if there is something else causing the high CO. I have posted in the "Wanted" section in case someone has a known good sensor I could buy, and also looking at replacing the (seemingly original) exhaust system.
Any advice or morale boost much appreciated!
David
 
Liverpool is not a million miles from Stoke on Trent where the mighty WOM Automotive are to be found. They might well be able to help.
 
X495 said:
Hi All
I am having a saga getting our 2000 1.4 AUA (Po) through the MOT. A few jobs fixed but currently stuck with high CO reading, MIL and P0135 fault code. Front lambda replaced with brand new (Bosch however rather than NTK). P0135 now triggers immediately and persistently (it was sporadic with the original sensor). Auto elec suggests the new sensor is faulty.
Do I bit the bullet for a new NTK one? I am wondering if I have two underlying problems though, and if there is something else causing the high CO. I have posted in the "Wanted" section in case someone has a known good sensor I could buy, and also looking at replacing the (seemingly original) exhaust system.
Any advice or morale boost much appreciated!
David
Click to expand...
I'd be surprised if a brand new, genuine Bosch sensor was faulty.
Get it hooked up to vcds, and find out what's going on. Guessing, by you, us, or your mechanic, will be expensive and frustrating in equal measures. Check the scan register to see who's local.
Mac.
 
I'd run some cataclean through the system and see where you are after that. Has worked wonders on a number of my 1.4's with high readings in the past.
 
Thanks all. It's got cataclean in it but needs running through. The guy who looked at it came highly recommended as an auto electrician/diagnostics. I hadn't appreciated that it might need a VW/Audi specialist system.
 
X495 said:
Thanks all. It's got cataclean in it but needs running through. The guy who looked at it came highly recommended as an auto electrician/diagnostics. I hadn't appreciated that it might need a VW/Audi specialist system.
Click to expand...
Does the 1.4 have pre and post lambdas? If so, which one is giving a high C0 reading?
Mac.
 
Yes, pre and post cat lambdas. High CO is coming up on the MOT emissions test at tailpipe. Only fault code showing on my cheapo reader is the P0135 (Bank 1, Sensor 1, Lambda heater circuit).
 
X495 said:
Yes, pre and post cat lambdas. High CO is coming up on the MOT emissions test at tailpipe. Only fault code showing on my cheapo reader is the P0135 (Bank 1, Sensor 1, Lambda heater circuit).
Click to expand...
If that's the pre cat lambda, (I think it is), then cataclean won't help.
High CO pre cat indicates poor combustion chamber burn.
If you aren't getting any misfire errors, compression check, check inlet air filter.
Mac.
 
PlasticMac said:
If that's the pre cat lambda, (I think it is), then cataclean won't help.
High CO pre cat indicates poor combustion chamber burn.
If you aren't getting any misfire errors, compression check, check inlet air filter.
Mac.
Click to expand...
that's the one we had the same error on until I put a new NTK VZA11-V1 lambda on, fixed it overnight.

Nb. could this instead be indicating an issue with the loom wiring or connector for the lambda?

edit of edit.
3 or 4 MOTs ago (having replaced throttle body with new one, EGR, plugs, cables, and eventually the coil in stepwise refurb of a poorly maintained AUA), at the MOT it became clear that the original lambda was goosed and had been causing rich mixture which in turn had poisoned the catalytic converter (which also needed replacing) ; a new but generic lambda was fitted as part of this fix. MOT was then passed. However over last 18 months increasing number of engine lights and other issues invoking the engine light, with repetitive mixture / MAP sensor / lambda heater open to earth / all the ABS/ESP lights etc. going on). New genuine lambda solved these a few weeks ago.

Could the CO issue be caused by a cat that has gone bad downstream of a failing lambda giving spurious signals and causing over-fuelling?
 
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PlasticMac said:
I'd be surprised if a brand new, genuine Bosch sensor was faulty.
Get it hooked up to vcds, and find out what's going on. Guessing, by you, us, or your mechanic, will be expensive and frustrating in equal measures. Check the scan register to see who's local.
Mac.
Click to expand...
@Robin_Cox thats what I thought until I bought one for £124 put on the customers car & the EML still on, looked at the values on the scanner all showing problem with the new sensor, I thought it must be something else causing it, kept trying with no luck, had an old twisted oily,old,horrible looking sensor that was probably 18 years old, put that on the car & all perfect, send the brand new sensor back to the supplier, its been 5 years, the old sensor is still working, amazingly.
 
If here is s small leakage in the exhaust system AFTER the lambda sensors, I suspect air can be sucked in and cause too high CO measured at the tail pipe, even though it is correctly at the sensors.
But solving the heater circuit error code is also a good idea to assure good operation before the sensor finally gets up to temperature by the exhausts.
 
Ami said:
@Robin_Cox thats what I thought until I bought one for £124 put on the customers car & the EML still on, looked at the values on the scanner all showing problem with the new sensor, I thought it must be something else causing it, kept trying with no luck, had an old twisted oily,old,horrible looking sensor that was probably 18 years old, put that on the car & all perfect, send the brand new sensor back to the supplier, its been 5 years, the old sensor is still working, amazingly.
Click to expand...
I think this is a cross-post - I didn't recommend a Bosch - I've had good luck with a new NTK / NGK sensor, not the Bosch one in experience recently. I normally trust Bosch for most things, but after our non-OEM generic lambda garage-fitted experience ; afterwards when I got the recommended NTK/NGK for an acceptable price and it worked, I've been a firm advocate for what I was told were the original supplier for AUA lambdas on this exact point - and it appears to have been successful. (bearing in mind that I'm also an advocate of Mahle and Febi-Bilstein not quite original manufacturer parts for an awful lot of parts because they are generally suitable quality in my experience).
 
Thanks all for the replies. I had wondered about the possibility of the cat being contaminated. I've managed to find a new NGK LZA11-V1 at a reasonable price so am going for that to see if I can at least address the EML and PO135 code. Will keep you posted.

David
 
I think @PlasticMac is heading down the right path. Compression test first as if you have a broken exhaust valve the cat will be goosed due to incomplete combustion. Does it run smooth otherwise?

Ian
 
Quick update as we're staying at the inlaws: swapped the original lambda back on, it still threw up p0135 code but when cleared the code stays off for a few mins. I chanced a retest on the emissions which it passed, so am now celebrating an MOT pass. Next step the new NGK lambda to see where that puts us. Interested to try compression test too. Runs well but not as quiet/smooth as I'd like.
Thanks all for your help.
 
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X495 said:
Hi All
I am having a saga getting our 2000 1.4 AUA (Po) through the MOT. A few jobs fixed but currently stuck with high CO reading, MIL and P0135 fault code. Front lambda replaced with brand new (Bosch however rather than NTK). P0135 now triggers immediately and persistently (it was sporadic with the original sensor). Auto elec suggests the new sensor is faulty.
Do I bit the bullet for a new NTK one? I am wondering if I have two underlying problems though, and if there is something else causing the high CO. I have posted in the "Wanted" section in case someone has a known good sensor I could buy, and also looking at replacing the (seemingly original) exhaust system.
Any advice or morale boost much appreciated!
David
Click to expand...
Hello All.
I commented a while ago about my 1.4 AUA petrol 2001 car. I replaced the pre-cat Lambda sensor, and it cured the
engine management light. I bought an NTK from Only Sensors for about £56 in early 2020.
It passed the MOT at Victoria VW/Audi in Broadstairs with no advisories in April 2020.
In 2021, I took it to a general garage nearer me for the MOT.
The low petrol light had been on for about 8 miles prior to the MOT.
It passed again with no advisories, but the tester said; please make sure it's got more petrol in it next time,
as he had trouble getting it through the emissions test.
He didn't specify the particular aspect of this difficulty. I was just pleased it passed. It had only done about 3000 miles during the year.
This may be irrelevant to your problem, but of interest to others.
The next MOT is due soon, and I'm a bit worried about the condition of my exhaust, especially the pipe forward of the rear silencer. I believe the whole system is the original, with a mileage of 170,000.
Any tips on replacement exhaust parts would be welcome. Thank you.
Good luck.
 
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GMH499 said:
Hello All.
I commented a while ago about my 1.4 AUA petrol 2001 car. I replaced the pre-cat Lambda sensor, and it cured the
engine management light. I bought an NTK from Only Sensors for about £56 in early 2020.
It passed the MOT at Victoria VW/Audi in Broadstairs with no advisories in April 2020.
In 2021, I took it to a general garage nearer me for the MOT.
The low petrol light had been on for about 8 miles prior to the MOT.
It passed again with no advisories, but the tester said; please make sure it's got more petrol in it next time,
as he had trouble getting it through the emissions test.
He didn't specify the particular aspect of this difficulty. I was just pleased it passed. It had only done about 3000 miles during the year.
This may be irrelevant to your problem, but of interest to others.
The next MOT is due soon, and I'm a bit worried about the condition of my exhaust, especially the pipe forward of the rear silencer. I believe the whole system is the original, with a mileage of 170,000.
Any tips on replacement exhaust parts would be welcome. Thank you.
Good luck.
Click to expand...
Hi GMH499
You got a bargain with your sensor! My genuine NGK one is due to arrive tomorrow, but I may wait to fit until the weather is a bit better...
Hope your MOT goes ok too. I had the same thought about exhausts. I looked to replace but was surprised how difficult little availability three seemed to be.
David
 
X495 said:
Hi GMH499
You got a bargain with your sensor! My genuine NGK one is due to arrive tomorrow, but I may wait to fit until the weather is a bit better...
Hope your MOT goes ok too. I had the same thought about exhausts. I looked to replace but was surprised how difficult little availability three seemed to be.
David
Click to expand...
Hello David.
The NTK sensor was a bargain at the time. Their price increased to £75 soon after; but I think it went down again
later. I haven't checked the price for nearly 3 years now.
At the time AUDI wanted £300 for a new sensor, and Euro Car Parts £285 (WOW, which was also an NTK).
My new one came with the correct plug, and a longer cable; whereas the old one was really too short.
The sensor is easy to change from underneath.
Remove the undertray, and use a 22mm or 7/8'' AF open-ended spanner.
You don't need the special wrench which is supposed to make it easy from above. It doesn't (£10, I wasted).
No comment was made about the exhaust condition last year (at Victoria's again). I'll leave it and see if it's commented on.
I'm fixing the advisories at the moment;-
Front brake discs, front amber indicator bulbs, windscreen wiper (pivots now replaced by Depronman). I've checked the 4th advisory about the rear brake pipe being rusty and coated with grease or similar. I can't feel anything wrong with it; the tester was being picky!!
Regards, and good luck. Keith.
 
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Well I can add a "+1" to the suggestion of only going for an original NTK front lambda. I fitted it yesterday and no MIL now or fault codes. EPC light came on briefly but has not re-appeared. 12 months clean MOT is a good result. To add to Keith's post above, I paid £75 for the NTK sensor. The Bosch one (which had shown equivalence in the books) was £50 but threw up a fault code straightaway. No point in going for anything other than NTK based on my experience. Thanks all for your help, David.
 
X495 said:
Well I can add a "+1" to the suggestion of only going for an original NTK front lambda. I fitted it yesterday and no MIL now or fault codes. EPC light came on briefly but has not re-appeared. 12 months clean MOT is a good result. To add to Keith's post above, I paid £75 for the NTK sensor. The Bosch one (which had shown equivalence in the books) was £50 but threw up a fault code straightaway. No point in going for anything other than NTK based on my experience. Thanks all for your help, David.
Click to expand...
Glad I've been some help David, and that the NTK sensor is still a reasonable price.
I've had no more EPC light trouble caused by the Lambda sensor, but only by
a faulty fuel injector on no.3 cylinder in June last year. The RAC man initially diagnosed an
ignition fault and replaced the coil and leads. It made no difference, and then reckoned it was an injector,
and with the assistance of a second RAC man (they couldn't have been busy) confirmed that it was.
It was now too late on a Saturday to get one, and I was towed 40 miles home.
I got the first guy to replace the ignition parts ( £180, at their prices ) with my original set.
I managed to find a New Old Stock genuine injector for £127 online, and fitted it myself. I haven't
had any warning lights or problems since.
I believe the genuine AUDI injectors for the AUA engine are obsolete, though I was quoted about £220 each by a friend
who works for AUDI, but he later found that they're unavailable. Can others confirm this?
A Bosch one ( £65 ) from JAYAR Motor Factors which was supposed to be a replacement wasn't the same, which was why
I had to get the NOS item.
I did change the original AUDI coil to a German made Topran, + Bosch plugs and leads due to a minor crack on one coil HT outlet. Cost for all these was £75.
Thankfully you've got your new MOT.
Regards, Keith.
 
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