Sherlock Holmes needed engine management light x 5

[Stiglet]

Anyone want a mystery . I have the lovely amber engine management light on again for the 5th time... So far

Replaced all coil packs
Replaced all spark plugs
Replaced pre cat lambda sensor
Replaced post cat lambda sensor
Had cat tested and that proved ok
Cleared all fault codes.

All was fine for about 3 weeks again then on comes the light, seems to stay off for about 2-3 weeks then comes on ? Any ideas please as it's driving me mad!! The engine appears to be running fine? I will have to look up previous fault code number for you as it's bound to be the same..

Spend almost £500 so far and light is still there....

16804 P0420 Catalyst System,Bank1 Efficiency Below Threshold is the code I'm getting.

 

[S7UYJ]

Has anyone tested the sensors since they were fitted. As you probably know the code means the cat isn't doing its job right, and the sensors are what tells the car this. So if a connector has failed, or the wiring is damaged, you can change the sensors as many times as you like but the problem will still come back.

If your not getting any other codes I doubt it's a misfire or anything like that

Easy to damage wires when changing a sensor too so may have been faulty, replaced but wiring damaged so still throws a light.

Hope this helps a little!

 

[S7UYJ]

Out of interest, how was the cat tested? I didn't know it could be done?!

 

[Stiglet]

Thanks for your reply. Each time a sensor has been replaced it has worked ok for about 3 weeks then throws a light. As for the cat it was hooked up to a mot testing machine for emissions and the readings were fine. The guy who did it says you can soon see by the readings if the cats gone. I'm thinking maybe cats ok but on way out or I've seen another thing on the net saying even a hole in the exhaust can cause a light. Think I need it properly tested by a exhaust place?

 

[MATT RILEY]

Check your egr valve sounds like its sticking open so your cat is not getting hot enough to work properly.

 

[Stiglet]

Check your egr valve sounds like its sticking open so your cat is not getting hot enough to work properly.

Many thanks Matt, I will pass this on to my garage to have a look at. Really appreciate it.

 

[Stiglet]

Garage just turned the light off but it's recording the same code as before. They are stumped and are phoning vw tomorrow for ideas? They don't think it's the egr...

 

[JJBSpain]

any update and/or did you resolve?

 

[Stiglet]

I've reposted but still on going. They can't find the EGR Valve? They are contacting seat to find out if I have one and where it is. I've even taken Haynes manual to the garage and that didn't help. My next option is to get the cat properly tested as it may only be 94% working and that's enough to trip the EML light....had this problem for 6 months now...

 

[NWhiteley]

Was it a cheap/budget cat you had fitted, or a good quality one?

I once had budget cat fitted which would sometimes pass the MOT emissions test and sometimes it wouldnt, the cat was changed 3 times and still had the same problem, i then paid the extra to have good quality cat fitted, although i cant remember if it was a dealer part or from Bosal, but it worked first time and never had another problem with it.

 

[Stiglet]

I'm still on original cat. Not had it replaced yet... I say yet lol. But I'm looking to sell car soon so may have to get it done . I'd never sell my car not running right. Totally unfair..

 

[NWhiteley]

aahhh sorry, i read it as though you have had the cat replaced. Please ignore me then.

 

[Stiglet]

aahhh sorry, i read it as though you have had the cat replaced. Please ignore me then.

Lol ok no probs cars only done 37000 but I think short journeys may have killed it?

 

[AaronWCupra]

Ever sort this problem out?

 

[Stiglet]

No lol, had light reset and road works on m25 went and it's been fine since .? Weird the roadworks did limit me to 50mph for about 8 miles... But since they went and I've been doing 80mph it's been fine, duno if I've cleared the cat out a bit? Really strange...