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Discussion Starter #1
My V-6 Laguna 2 is displaying this fault on a reader. The fault has been occurring on and off for the last couple of years, I reset it and it stays ok for some months, then comes back. The car's behaviour is a slight stumbling when under load, but otherwise it's fine. But I don't know what it means, and what needs to be done to fix it permanently. The car has only done 146,000 miles. The fault displays for both Rail 1 and Rail 2.
Any help welcomed. I searched the database, but could not find any reference.
 

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Without knowing what about the fuel trim the scanner/car is complaining, its going to be virtually impossible to suggest what to do ............. you need a better/more competent scanner to say whether its running too rich, too lean or whatever and that info comes out of a code
 

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Discussion Starter #5
I can read all sorts of more data, but I don't know what to look for. It's all numbers, not codes, though, and I don't know what numbers are good or bad. My next stop was going to be my local garage, which has a real reader. I was just hoping that there was a common fault that keeps on coming up.
My Laguna has followed all the correct fault paths:
Blocked drain tubes, failed window regulators, self-smashing rear window, failed heater fan, flashing backlight on climate control display. Its only unusual one appears to be a broken driver's door lock mechanism. Otherwise, I love the car.
 

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Ok lets try - can you get numbers for the long term fuel trim on bank 1 and bank 2?
 

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Discussion Starter #7
This will be tomorrow, but I will see what I can get. The scanner powers down as soon as it's disconnected from the car, so I can't bring it indoors to my PC to look at the readings.
Is there any specific item description to look for? "Long term Fuel Trim" rings no bells as a line in the listings.
Otherwise, I'll read everything, and take photos of each screenful.
 

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Your vehicle should be EOBD and that means that the most important fuel governing mechanism on the vehicle is the long term fuel trim values .............. most all scanners should really be giving you that as a minimum.................

Perhaps screenshots of everything would be better since we don't know what scanner you have and what its reporting
 

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Discussion Starter #9
Ok, we have information.
1. The fault codes are: P0170, for bank 1, and P0173 for bank 2.
2. Freeze frame readings were: FUELSYS1 : CL; FUELSYS2 : CL; SHRTFT1(%) : -15.6; LONGFT1(%) : -23.4; SHRTFT2(%) : -14.1; LONGFT2(%) : -20.3.

I don't know what these numbers mean in real life.

The scanner is a cheap and cheerful Konnwei KW 808. It does not pretend to be very sophisticated, but somebody who knows his way around CANBUS and OBD11 may well be quite competent with it.
Me, I'm happy with twin SUs, thank you.

Does this make any sense? I have digital photos of the screens, so I can get more info, but this seems the most important at the moment. There is in fact not much more data, just temp. and rpm etc.

Thanks for the help.
 

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Twin SUs were the bomb yes ................... last ones I had to tackle was on a B18 Volvo ................... but oh so long time ago

Ah - Good results in that case.

The LTFT values you report indicates the engine is possibly running way rich and is constantly having to lean out the mixture (the -23.4 and -20.3).....................thus the dash complaint - the LTFT values are supposed to be close to 0 (around 5% only ) on a normal engine in good condition and good service history.

So now the question is why................

If you have decent quality spark plugs in known/proven good condition (proven by replacement ?), then my next guess would be a funky upstream O2 sensor.

Can your scanner produce graphs? ...................... and if so can you post one of the upstream O2 sensor (O2B1S1 parameter) voltage behavior while the engine is idling and hot

Can you give us your specific model code or VIN so we can see about instrumentation details?
 

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Discussion Starter #11
That sounds promising.
No graphs, I'm afraid. Too cheap for that.

Looking at the pictures, I don't see any readout for O2B1S1, although it is referred to in the scanner manual generically. Which makes me think that somewhere it may not be visible to me. I'll look tomorrow, maybe it's on a different screen, but there didn't seem to be much more anywhere.
The VIN is : VF1KG0D0B26135596

Over time, the car has had maybe 4 of the coil-caps replaced. Could another failure cause this? None of the others showed this fault, they all displayed as "Misfire"! Also, they would not Reset successfully until the cap was replaced.

Is it worth buying a new spark plug(s), and moving it around to see if there is any effect? I don't relish removing the rear ones without a known reason, they are well covered back in there. The age of those there could be anything.

One question: Is the reference to Bank 1 and Bank 2 the same as the two rows of cylinders?

Thanks again.
 

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Your scanner can do graphs ............... this guy did exactly the one I am looking for


The plugs and coils:

Yes - any misfire will cause a rich reading on the O2 and thus incorrectly direct the ECU to lean the mixture - I would start by replacing the plugs as a minimum.

Bank 1 and bank 2 ................yes - you have that right
 

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Discussion Starter #13
Well, well. That's worth knowing. This scanner is more intelligent than I thought.
I'll try tomorrow and see what happens.
Re: Bank 1 and Bank 2. Every time this fault has occurred, it has always been both banks. Does this point in any particular direction as a diagnosis?

Obtaining a set of new plugs might take a few days in this time of lockdown.

Cheers.
 

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Is it worth buying a new spark plug(s), and moving it around to see if there is any effect? I don't relish removing the rear ones without a known reason, they are well covered back in there. The age of those there could be anything.
Unfortunately that reaction is quite common from both owners that do self-service as well as workshop personnel ................ and is often the cause of exactly the moans you now experience because the rear set of plugs get "skipped" during a service and eventually they start REALLY misbehaving ....................... if you already are also saying

The age of those there could be anything.
then there can be absolutely no harm in replacing ALL of them and starting with a known good reference position.

I asked for your specific model/Vin so we can possibly check on instrumentation - in particular the number of O2 sensors fitted. Unfortunately the Renault reference material also sometimes is not 100% to be believed on this particular subject (proven quite recently on exactly this motor with the O2 playing up as well) ................... so :

The reference material would suggest you have 4 O2 sensors ..................2 upstream and 2 downstream of the CAT ............ can you physically confirm your own situation? ................ some engines also came with a single upstream O2 sensor and a single downstream O2 sensor

Re: Bank 1 and Bank 2. Every time this fault has occurred, it has always been both banks. Does this point in any particular direction as a diagnosis?
If you have a single upstream O2 and a single O2 downstream (and not a set per bank with also 2 individual CATs), then the plugs thing may indeed be the responsible for your moan ............ other ugly goodies suspect AFM, MAP, injectors, O2s themself etc etc etc - lets start with the obvious suspects first (plugs)

If however you have 4 O2s, then things can get very ugly very fast .....................

Please also confirm your engine coolant temperature parameter's value - does it make sense to you - iow - around 15C cold and around 90C when engine hot
 

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Discussion Starter #15
I'll see what I can find. Unfortunately, the battery voltage dropped to 6 volts overnight, so today it's recharge it and find out why it happened. The alarm seems to be permanently activated.
I'll look at my previous garage invoices for coil-cap work, and see if there were any plugs included.
Misfire debug on hold temporarily (I hope!).
More news when available.
 

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On these motors I wouldn't put a lot of faith in a reported and paid for plug replacement on the rear bank unless you did it yourself, but that is just me being miserable
 

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Discussion Starter #17
The last time the car was in for a rear bank coil-cap replacement, they moved them around so that the ones at the back were all newer ones, and unchanged ones were all at the front, where they can be got at. I didn't ask for new plugs, but if they are on an invoice, I will believe that Sean replaced them.

I see various plugs available online: Bosch Double Platinum seem to be promoted, are they certainly the ones to go for? The price is pretty good, too. I have one new Bosch available right now.

No pictures of graphs yet, but I did view the SHRTFT1(%) and SHRTFT2(%) graphs. No. 1 showed a kind of sawtooth pattern, with frequent drops and rises. No. 2 showed very stable sawteeth, with long periods at the max. 25 volts. I'll get a picture later.

No news on O2 sensors yet. Should they show up in the scanner list, or do I need to get underneath and physically look? That may take some time!

The battery problem was the Emergency Flashers being left on accidentally overnight, presumably when I left the car after the last scanner operation yesterday. Hopefully, all sorted.

Thanks.
 

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Short term fuel trim is useless as a tool unless you know for a fact that the O2 upstream is working - start there and get the O2 upstream voltage graphs first WHILE IDLING

With the battery having died overnight its also going to be a crap-shoot now for a while - I would suggest get the engine warm and take it for a drive - come back and let it sit idling for about 5 minutes ................... all your adaptations learned by the ECU is bound to have been reset and any current values is a waste of time as a faultfinding method/tool

On the scanners I have all the O2s will show up, but I cannot speak for your particular scanner's abilities to speak the truth ............... you may have to go take a look at the actual animals found on the engine - if you have 2 upstream O2s then you will also have 2 downstream O2s ................ so just have a look-see under the bonnet on the exhaust runners to the CAT - no need to get under the car
 

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Discussion Starter #19
The scanner shows that there are 4 O2 sensors.
It also shows that none of them have anything other than 0.0 v. This is when idling after a short run.

Hmmm. Maybe a full set of O2 sensors as well as spark plugs, or some wiring or ECU trouble?
 

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Nope - hang on before you start spending good beer money on O2s ..................

Chances of all 4 O2 going funky all at the same time is just about 0 imo.

There has to be at least one of them producing a signal other than 0V surely? ...................... switch off ignition ............. go have a beer.

Come back 10 minutes later and switch on ignition without starting engine ............. start your scanner - you should now be seeing around .45V on all the O2s else there is something very basic wrong like a missing 12V heater supply on them all ................or the scanner is a liar .................

Do you smell raw fuel in the exhaust perhaps?
 
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