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Technical Lambda senor nightmares

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Technical Lambda senor nightmares

quaffle

quaffle

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Mar 9, 2011
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Hello all,

So a little while back my engine management light appeared on the dash.

Plugging a code reader/diagnostic gave the the following error message:

P0420 Catalyst System Efficiency Below Threshold Bank 1

In the past, I had to change the catalytic converter to a new one as the old one developed a crack. I'm using the new cat now.

I'm pretty sure the catalytic converter is working fine as it's passing it's MOT getting normal results in emissions.

I had to cut the top (pre-cat) lambda out as it was rusted in when changing catalytic converter and I thought I might have damaged it during the process.

I bought a new 3rd party lambda sensor. This one exactly.

It went in OK but now I'm getting these engine management codes.

Please click for Imgur album

The original error code has gone (yay?) but now I'm getting these.

Any ideas guys? I'm lost on this one.

Fiat Punto 1.2L 16v Active Sport 2003

Cheers.
 
Last edited:
the code is complaining about the heater in the sensor.


So IMO it's either


1. The heater being open circuit
2. Incompatible sensor in terms of pin out
3. Wiring loom fault


You could swap pre with post lambda sensor to see if the error shifts accordingly
 
atom0007 said:
the code is complaining about the heater in the sensor.


So IMO it's either


1. The heater being open circuit
2. Incompatible sensor in terms of pin out
3. Wiring loom fault


You could swap pre with post lambda sensor to see if the error shifts accordingly
Click to expand...
The wiring looks okay.

Are they the same sensor? Is the back and front sensor interchangeable? I can't seem to find my exact model on their catalog sheet.

Can you see what the model should be and I can see if it matches it on the box? It might be a case that it's the wrong sensor model as you said.
 
MikeSalt said:
You say the wiring looks OK, but have you sprayed contact cleaner at both the ECU-loom junction and the loom-sensor junction?
Click to expand...

Could that really be the errors are showing?

Am I best off just getting an official one from Shop4Parts or can I fix this issue some how?
 
My tuppence is that's it's unlikely to be dirty contacts, the AMP connectors have oil proof seals.


But no harm in trying


You could probe the heater resistance if you know the pin out to check that it is working OK.


I couldn't cross reference the EPER number either, the manufacturer might be able to help via email/phone


If I was in your position, I would get a reasonable looking part from the scrapyard....I've certainly done that before.
 
Was the Cat you've fitted actualy new or is it a used one?


if it is a used one..id buy some Cat'a'clean,




New lambda sensors can be actualy faulty.
you have the right to Return it and ask for replacement/refund,
 
quaffle said:
Could that really be the errors are showing?
Click to expand...

Oh yes, spent hours and lots of money replacing the sensor, only to discover that it was the ECU to wiring loom connector. It's never been unplugged as far as I know, all the dust deals were intact, contacts looked clean. My theory is that it had glazed with old age on the connectors because contact cleaner solved it.
 
atom0007 said:
My tuppence is that's it's unlikely to be dirty contacts, the AMP connectors have oil proof seals.


But no harm in trying


You could probe the heater resistance if you know the pin out to check that it is working OK.


I couldn't cross reference the EPER number either, the manufacturer might be able to help via email/phone


If I was in your position, I would get a reasonable looking part from the scrapyard....I've certainly done that before.
Click to expand...

I'll look into these options, thanks.

oldhammer said:
Was the Cat you've fitted actualy new or is it a used one?


if it is a used one..id buy some Cat'a'clean,




New lambda sensors can be actualy faulty.
you have the right to Return it and ask for replacement/refund,
Click to expand...

The cat was 100% new when I bought it.

I guess sending it back might be an option if I can't figure this one out.

atom0007 said:
Also, swap them round now you've confirmed they're the same and see if the error moves
Click to expand...

The thing is, the FAE catalog that I linked to in a post above says that they're not the same. Seems to be some conflicting information here.

MikeSalt said:
Oh yes, spent hours and lots of money replacing the sensor, only to discover that it was the ECU to wiring loom connector. It's never been unplugged as far as I know, all the dust deals were intact, contacts looked clean. My theory is that it had glazed with old age on the connectors because contact cleaner solved it.
Click to expand...

No harm in trying this I suppose but it's weird it's just happening now after changing it. Thanks for the response guys.


I'll try and confirm if it's the right part with FAE's support team if possible.
 
having a similar problem with me automatic ELX. Replaced sensor and still getting fault codes, sometimes within a day, sometimes it would go for a couple of weeks.

Unrelated, we could smell fuel when in the car, so had my mechanic check out the pipes, had one replaced near the steering, then realised that there's a pipe which deals with fumes in the drivers side rear wheel arch which was completed shredded.

The mechanic suggested that this could be bringing air into the engine and causing the lambda sensor to have a fault. We reset the code since his temporary repair (didn't have parts when we realised this pipe was dead) but I haven't had a chance to drive it yet because of another leak elsewhere.

Might be worth just checking that out?
 
drivingmooma said:
having a similar problem with me automatic ELX. Replaced sensor and still getting fault codes, sometimes within a day, sometimes it would go for a couple of weeks.

Unrelated, we could smell fuel when in the car, so had my mechanic check out the pipes, had one replaced near the steering, then realised that there's a pipe which deals with fumes in the drivers side rear wheel arch which was completed shredded.

The mechanic suggested that this could be bringing air into the engine and causing the lambda sensor to have a fault. We reset the code since his temporary repair (didn't have parts when we realised this pipe was dead) but I haven't had a chance to drive it yet because of another leak elsewhere.

Might be worth just checking that out?
Click to expand...

The wheel arch breather has absolutely nothing at all to do with the lambda issue.
 
Twotoncarman said:
The wheel arch breather has absolutely nothing at all to do with the lambda issue.
Click to expand...

drivingmooma said:
Good to know. It was just a suggestion the mechanic had re bringing air into the system somewhere and causing a problen with the sensor.
Click to expand...

atom0007 said:
New mechanic time...
Click to expand...


Agree'd he doesn't know what he's doing then

The fuel system leak wont make the lambda's report faults unless there is an extreme case of low pressure, and you'd be getting lacking power and possible misfiring then

Which you aint got
 
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