Emissions light (codes 16555 & 16786 & 16804)

[Tim1111]

Hope someone can help me sort a problem on the wife's Golf (2003 1.6 16V - BCB I think from memory).

Emissions light has come on 3 times in the past month. I've cleared it each time and it stays off for about a week or so then reappears. Each time it throws up 3 codes:
16555 - P0171: Fuel trim - System lean (Bank 1)
16786 - P0402: Exhaust gas recirculation flow excessive
16804 - P0420: Catalyst system efficiency below threshold (Bank 1)

She had a hole in the front exhaust which I've bandaged up hoping that was the cause (apparently not as it's just come on again :(). But still get the occasional chugging on idle (bounces up and down between 600-900 rpm, rather than it's usual constant 700ish). I also noticed when I drove it on the motorway the other day on a long journey that occasionally (happened twice in about 2 hours) the revs dropped off momentarily - cruising along then the revs dropped down to about 2500 then returned to normal all in less than a second.

One other point to note is that the light seems to come on after I've driven it (may be coincidence or could be my heavier right foot).

Anyway, over to you guys. Can someone point me in the right direction of possible causes to investigate?

Thanks for your help
Tim.

[Guest 2]

not sure if these will help

16804/P0420/001056 - Ross-Tech Wiki (http://wiki.ross-tech.com/wiki/index.php/16804/P0420/001056)

16786/P0402/001026 - Ross-Tech Wiki (http://wiki.ross-tech.com/wiki/index.php/16786/P0402/001026)

16555/P0171/000369 - Ross-Tech Wiki (http://wiki.ross-tech.com/wiki/index.php/16555/P0171/000369)

[Tim1111]

Cheers Chris.

It looks like from these likely causes could be:


Leakage in Intake and/or Exhaust System
Catalyst faulty
Oxygen Sensor(s) faulty
Oxygen Sensor(s) Control faulty
Exhaust Gas Recirculation (EGR) Valve stuck open/leaking/faulty
Exhaust Gas Recirculation (EGR) System leaking/faulty
Wiring and/or Connector(s) from/to Exhaust Gas Recirculation (EGR) Valve faulty
Mass Air Flow Sensor (G70) defective
Intake System Leak(s)


Question is, would any of the above be likely to trigger all three codes each time and therefore be the most likely culprit?

[Crasher]

I would be suspecting the EGR valve, be aware that if you fit a new one it has to be adapted to the ECU and tested for function or the new valve can burn out. If her car has the early steel bodied (usually rusty) EGR valve then I would doubly suspect it. The later ones have a black plastiky looking ribbed body.

[Tim1111]

Thanks Crasher.

Is there any way to confirm diagnosis / test EGR? Is this a replacement job, or does it just get gummed up and need a clean.

[Crasher]

Quite easy to test if you know how in Basic Settings 04, group 075.

[Tim1111]

Sounds like I'll be needing someone near me with VCDS then? I'll utilise Chris's handy map in his signature above.

If it is the EGR, is it a replacement or potentially just a clean up job? Will VCDS be able to identify if it's knackered or just needs cleaning?

[Crasher]

They do not respond to cleaning UNLESS the code is low flow in which case it is usually the outlet of the EGR pipe being blocked. It may come up as a conclusive fault code, there is only one way to find out. You don't just need someone with VCDS, it is VCDS+ skills to use it. Just owning a copy of VCDS does not make one a diagnostic God! Most private owners only have free VCDS Lite which is next to useless or Lite registered if you are lucky and even then they spend their time barking at the fault codes or misinterpreting them and don't even get me started on Measuring Block data interpretation! Sorry, ranting again-just had dealings with someone just like above and irritated me...

[Tim1111]

It's good to get these rants out of your system.

Thanks for all the help and advice Crasher. I'll wait for the codes to reappear as I cleared them last time to get rid of the light - on recent experience it could be a few weeks before they reappear - and then see if I can find someone competent with VCDS to check it out for me without charging ******* prices.

how odd, the forum has automatically starred out me calling a dealer a st**ler in my post - is that word not allowed? I shall be expecting a knock on my door for a slap on the wrist for using such offensive language!!

[Crasher]

It was on my instigation many years ago, I find inferring that the main dealers are thieves offensive.

[Tim1111]

Fair enough - they are a business and there to make money, rather than a charity to provide us with cars and services at below cost price which some people seem to expect.

in my limited experiences with them I have found them friendly, knowledgeable and helpful - although there will always be others out there with other experiences.

Apologies for any offence I've caused to anyone.