Hi,

I've got a 2001 1.4MPI 8V Fabia.

Just had my car serviced, the garage said that it looks like I may need a new front Lambda sensor as the vag-com came back with;

16825 - EVAP Emission Control Sys: Incorrect Flow

P0441 - 35-10 - - - Intermittent

16556 - Fuel Trim: System Too Rich: Bank 1

P0172 - 35-10 - - - Intermittent

I had them clean the throttle body and check the air pipes, just in case it was that, but am waiting to see if the faults return.

They have quoted me 200 quid to replace the front lambda, is that right? (they reckon the sensor itself is around 140 quid).

(Personally, that sound a tad high, but what do i know?)

Haha just a bit, buy the part and replace it yourself, not a difficult one to do.

aye buy it urself mate, tbh that price for a genuine one does sound roughly right, there are always factor ones alot cheaper

Where exactly does it say in those codes that the Lambda probe needs replacing?, not to mention which one of the two probes is at fault? - It doesn't. What it is saying is that the probe has reported an intermittent rich mixture, which is its job. There is not a code there saying the heater circuit has had it or that there is no probe activity, which would mean that a new probe is required.

The intermittent rich mixture could be a direct result of the intermittent evaporative emissions fault. Clear the codes and see if they return, if they do look at the charcoal cannister solenoid first, which is easier and cheaper to replace than no.1 probe.

So it would say specifically that the probe was faulty?

The intermittent rich problem does re-occur, but I'd not had the throttle body cleaned before and the car has now done just over 55,000 miles.

I've never even heard of the charcoal cannister solenoid before, are they on the 1.4 petrol engines as well as diesels?

(Sorry to sound dumb here, just everything I'd heard so far kept bringing up the lambda sensor as a likely fault, the garage said 'bank 1' represented the first lambda probe, but I'd thought it meant bank 1 of the cylinders / fuel system).

For Lambda sensors try these guys:

Just Lambda for UK lambda sensor sales

I have used them in the past for my Golfs. Very good prices but best get a Bosch unit as they are OE spec. You'll pay around £100 for the part inc VAT & P&P

Not sure about fitting. My independant VW specialist charged me £25+ Vat to fit mine. (Needed special spanner and ramp to get to it)

HTH

Nick...

More details on the 16556 here:

16556/P0172 - Ross-Tech Wiki

As far as I know the charcoal cannister is exclusively used with petrol engines, it is there to prevent petrol vapour from entering the atmosphere. Its discharge of stored vapour is controlled by the engine ECU and fed into the inlet when the ECU sends a signal to activate its release solenoid. This solenoid could be playing up and causing the rich mixture.

In my experience, lambda probes show up one of two types of fault codes when they fail, one to say that there is no activity and the other to say that its heater circuit has failed.

Bank 1 does not relate to the first probe. If you imagine an engine with a Vee configuration, it has two banks of cylinders, each with its own exhaust system immediately after the cylinders, each of these exhausts will have a probe in it before the cat. Bank 1 is the first bank of cylinders and bank 2 is the second. As your engine is an in line 4 cylinder there will only be a bank 1. The probe is then given the designation S1 or S2, S1 is the first probe before the cat and S2 is the second probe after the cat.

So basically the garage have noted that it is too rich and have another code that could point them in the direction of the cause of it, however they have chosen to ignore it and have decided that it is not running rich at all, as the the probe must be giving wrong readings, and they can even tell which one it is.

How does the car drive? How's the power? Has the fuel consumption suffered?

Lambda or O2 sensors do get a bit "tired" with age and although they still send reasonable signals to the ECU and do not log a fault they can cause running issues. Whip the plugs out and have a look. See if they are sooted up and running rich. A good way of cleaning plugs and sensors is to get engine nice and hot then run at a fast idle of 3000rpm for about 3 minutes at no load. This should burn off any soot on the plugs and sensors as this is the optimum engine running speed for efficiency.

Also check wiring and temp sender connections. No need to rush to spend money if it is not needed. Most garage techs now seem to rely on what the computer says rather than good old fashioned mechanical diagnosis. These engines are fairly simple and not too difficult to diagnose properly with a bit of common sense. Maybe try a local independant VW Specialist. there should be one within 30 miles of you. Might save a few quid?

HTH

Nick......

More details on the 16556 here:

16556/P0172 - Ross-Tech Wiki

As far as I know the charcoal cannister is exclusively used with petrol engines, it is there to prevent petrol vapour from entering the atmosphere.

Thanks for the information!

EDIT: Just noted, one of the possible causes is an improperly seated dipstick, it could be nothing, but I have noted sometimes, the engine cover seems to "lift" the dipstick slightly and I have to push it down slightly to fully seal it, but I mean, I'm talking minimal here, it's not like the stick is hanging out or anything. (oo-err missus!)

Edited 30 September, 200817 yr by colkai

How does the car drive? How's the power? Has the fuel consumption suffered?

That's the odd thing.

Apart from the "normal" hunting at idle when stuck at lights / traffic, it's fine and dandy, getting upto 55mpg driven on M-ways at around 60-ish, around 48 if driven a bit more sharpish. Returns around 36-38 in heavy urban traffic, around 41-45 in "normal" traffic.

The only thing I have noticed, which has done since I bought it, is a slight lack of smoothness on the flow when going up hill and accelerating, but I'd hesitate to call it a misfire, just as, if anything, it is running a little lean.

That's why, until I saw this EVAP fault, I'd not been overly concerned as if the light came on, it inevitably went off again a day or two later of it's own accord.

Apart from all the "known" sensor faults it's had, the car drivers very nicely, go figure.

Funnily enough, the garage is an independent VW garage. :P

The hunting at idle and lack of smooth power delivery sounds more like the coolant temp sensor than the lambda sensor to me. Its a common fault with this engine, mine had it, and the £8 sensor sorted it, runs fine again now.

Yup, I've had that replaced last year.

Here's a question, would you expect a standard 10,000 service to include replacing the plugs?

Just I am wondering now if they have ever been touched / cleaned / replaced. Personally, I would of thought it should, but bar putting some hidden marks someplace, it's hard to tell, especially as the invoice jsut shows "full service".

Plugs are scheduled every 40,000 miles, as is the air filter.

Ahh, that's alright then, I checked my receipts from the work I've had done since I bought the car, (I do like to keep all paperwork ). I had new plugs fitted in 2006 not long after buying it so they've done about 20-25K since then.

Plugs are scheduled every 40,000 miles, as is the air filter.

Plugs are cheap to place and sometimes they can cause running probs if the rest of the engine is not in tip-top condition i.e. running lean/rich/advanced/retarded/lambda sensor issues. I always used ot replace my plugs every two years even though the car only did 6-7k per year and the service interval was 40k (platinum tipped plugs)