Long time, no post.
A quick summary of the problem...
52 plate 1.2 (3 cyl) 60hp engine Polo. It's done ~51k miles. It was
serviced (AFAIK) last September, it's 6 year service.
It's got an intermittent/transient problem where the CEL light comes
reporting a P0420 (inefficient cat) problem. When it does this, the
of petrol and uses a lot of fuel.
If left on its own, it'll go away after 48 hours.
When the light isn't on, then the fuel usage seems reasonable to me -
driven it to work, 70 mile round trip, and it's used ~20% of a tank,
a range of 350 miles, which is about right, certainly not massively
down on what
I would expect.
I've replaced the coolant temperature sensor (this has happened
replacing the CTS fixed it). It's had (some time ago) all 3 coil packs
It had a new dash pod last year (seems to be the main CAN hub - that
the entire car stops working)
The idle seems to be a bit on the slow/lumpy side (750rpm, and bearing
its a 3 pot!), and the car seems easier to stall than normal.
I'm not convinced that the problem *is*
in the cat, as the lumpy idle
it's at idle(!), and shoudln't be running in closed loop.
I'm not keen to take it to our local garage because (to paraphrase
read the codes, replace whatever it says, and move on from there".
code it flashes up is a weak cat, I don't want them to replace the cat
£500 all in), and maybe both lambda sensors (another £300 probably)
for this not
to be the problem.
I've got an ELM327 clone, plus some free software. The No1 O2 sensor
"N/A", the No2 O2 sensor shows (as far as I can tell from a 3Hz
that it's swapping between 0v and 0.9v at about 1Hz when running at
throttle on a flat road. Foot flat to the floor gives a constant 0v,
and coasting gives 0.99v constant.
As I understand it, if the car is being over-fuelled, it'll overwhelm
and the ECU may well then see the error as being in the cat, rather
highlighting the *actual*
I realise that the reason for the over-fuelling could be a leak
(either in the
intake or vacuum side, including crank case) downstream of the MAF. I
realise the problem could be in the upper O2 sensor - if it thinks the
too lean, it ups the fuel, floods the cat, which then brings up the
the sensor is weak, but still toggling, it may not be picked up by the
because it's still toggling, just slowly. I don't seem to be able to
figure from this sensor in the ODB software (just shows N/A as though
I also realise it could be the same thing that Honest John refers to
over-fuelling" on his review of this age/model/engine Polo.
So far, it's only done it on "short" journeys (i.e. about 5 minutes
journey). Normally it's put onto a motorway and driven at 60 (which is
3.5k RPM IIRC), but when it went on a shorter one, it then lights up.
Does anyone have any advice or suggestions for..
1) Order of checking/replacement of components? I've done the coolant
(wasn't it). It *should*
have had new plugs at its last service, but I
that a plug check should also be done. Is there any mileage in
removing the O2
sensor and checking its physical condition? If it's sooted up (due to
problem), cleaning it up?
2) Suggestions of other places to check like "9 times out of 10 it's
or the other>" I realise that lambda sensors have a life of about 50k
the car's now done 51k miles. How well protected is the connector
dirt/water ingress? My wife drove through what she thought was a
puddle but was
actually a pool of mud, and the state of the inside of the engine bay
nobody's business (same for the drive when all the mud under the
and fell off!)
3) A source of inexpensive parts! Cheapest I've seen a front Lambda
is £42 on ebay, and £199 for the cat. Many places (GSF included) don't
acknowledge the existence of the 1.2 3cyl engines.
4) Is it common for the rear wash wipe pipe to become disconnected
loom inside bay next to the gearbox? The squirter didn't work. I stuck
under the bonnet and got her to wash the rear window, and water
through what appears to be the tape-wrapped loom.
5) As I was removing the engine cover/filter assembly, I realised
there was a
rubber pipe from the filter box that leads to a cylinder which I
EGR (seems to be attached to the right hand side of the exhaust
then to the inlet manifold by a solid brassy coloured tube, about 2cm
diameter, and looks like the EGR on my car). This tube goes to the
bottom end of
the EGR, towards the bulkhead.
I don't know the function of this tube though. Could it be letting
in, when running in closed loop, to confuse the ECU? I've run the
(stationary) with the cover off, and there seems to be a slight vacuum
car's running, but it doesn't run any differently covered or not.
It's also done it with the pipe connected, so I'm assuming it's not
Many thanks for any assistance.