Lambda sensor error

[audi321]

Hi all. My sons 2016 Twingo has the EML on and when I read the codes it s coming back as a lambda sensor error. I can clear the code and the EML goes off but returns after approx 30 mins of driving.

Some questions for those who know significantly more than I do.

1. After dismantling to find them, I see 2 sensors (1 pre and post cat). I don t know which one is at fault as the reader I have doesn t tell me (launch 123). But is it likely to be the one before the cat?

2. It is likely to be the sensor itself or is there a bigger chance something else is wrong and there genuinely is a problem with the exhaust gases? ie do these sensors fail very often? The mpg is normal and it recently passed mot without any issue. Although it since has developed a hole in the exhaust back box

3. Not the best option I know but is there a hack to stop these altogether? ie code them out permanently or simply leave the connectors undone? He won t have the car much longer.

Or any other option?

Thanks all for any advice.

[paul_c123]

Would be worth fixing the back box then seeing if it cures the issue - it can mess up the validity of the reading the sensor takes, and the ECU interprets this as the fault you have.

I mean, you're planning to fix the exhaust anyway, right??

[audi321]

Ah right. I’d not thought of the 2 being connected. Yes back box will be replaced anyways but it would have been nice to fix this all together whilst it’s apart (engine in boot).

I’ll replace the back box and see what happens with the EML.

Thanks for the help

[stevieturbo]

Any proper scan tool will tell you which one.

If unsure, unplug the sensor to force a fault.

[Richard-D]

Launch CRP123 should tell you which sensor. Any tool that can read the engine code will do that.

What is the actual code?

You can't code them out as they're used to tell the engine ECU how much fuel to put in.

[audi321]

The DTC is 224413

[Richard-D]

audi321 said:

The DTC is 224413

That isn't the correct format for a DTC. If you go into the 'generic OBD2' menu of your code reader it will give you a code that follows a regular format. I'd expect it to be a letter followed by four numbers. Sometimes the menus that give you more information can add confusion and give strange results. The generic OBD2 menu will be fine for pretty much any engine fault.

[paul_c123]

Richard-D said:

That isn't the correct format for a DTC. If you go into the 'generic OBD2' menu of your code reader it will give you a code that follows a regular format. I'd expect it to be a letter followed by four numbers. Sometimes the menus that give you more information can add confusion and give strange results. The generic OBD2 menu will be fine for pretty much any engine fault.

Yes it is, for a Renault. I am guessing you have no experience working on Renaults. We have entered the black hole of "French electrics", where Renault do things a little differently from what you and I might call "logical". You need access to Renault service data to make sense of that code, though. Google won't reveal much, and the official service data isn't much better.

[Richard-D]

paul_c123 said:

Yes it is, for a Renault. I am guessing you have no experience working on Renaults. We have entered the black hole of "French electrics", where Renault do things a little differently from what you and I might call "logical". You need access to Renault service data to make sense of that code, though. Google won't reveal much, and the official service data isn't much better.

Yes, I appreciate that manufacturer specific fault codes do not necessarily follow this format. I was trying to give him the easiest route to finding the information he needs. I would expect him to be able to retrieve a fault code that is useful to him if he uses the generic OBD2 feature of his diagnostic scanner. That would enable him to see which component the ECU believes to be at fault.

[audi321]

Ok so quick update. Exhaust fixed, DTC cleared and EML came back on after 20 mins.

So back to my original question. Do these sensors often fail or is it likely there is something else wrong?

Then which one do I change? Pre or post cat? Or both?

Getting 49mpg even with the EML on so I don’t think anything is seriously wrong with the mixture?

[paul_c123]

The sensor sometimes fail and there may be something else wrong, eg wiring. It is unlikely (but possible) 2 things have failed at the same time.

To find out which sensor, get access to Renault service data or scan in OBD2 mode for a more meaningful fault code.

[SystemOfAFrown]

audi321 said:

Ok so quick update. Exhaust fixed, DTC cleared and EML came back on after 20 mins.

So back to my original question. Do these sensors often fail or is it likely there is something else wrong?

The can certainly just suddenly fail but their performance also slowly degrades as they age. However oxygen sensor trouble codes can also be caused by a multitude of other faults such as vacuum leaks, exhausts, wiring and connector issues.

audi321 said:

Then which one do I change? Pre or post cat? Or both?

As someone previously mentioned your scan tool should tell you which one is involved if you read the codes using the generic EOBD system, rather than the manufacturer specific diagnostic, even the ultra basic £10 unbranded scan tools can do this. The OBD code will start with a letter (P for "Powertrain" in this case) and four digits.

If the pre-cat sensor (typically shown as B1S1 in code scanners - Bank 1, Sensor 1) is a narrow band unit (it is on my wife's Dacia with the 0.9TCE engine) then you should be able to look at the sensor output voltage in the live data on your scanner and see it toggling up and down around once per second or faster if it's working and with the engine hot.

If you are going to fire the parts cannon at the car DO NOT buy unbranded oxygen sensors from eBay/Amazon etc. These things are frequently complete junk right out of the box. Stick with the Renault OE parts, or the OEMs like Bosch or NTK.

Edited by SystemOfAFrown on Monday 30th June 20:26

[audi321]

Well very interesting. After your posts I thought I’d borrow my mates cheapo OBD2 reader and read the code again (now it says 2 vs my Launch 123). Albeit they’re the same almost.

Here’s the result.