Hi

I have a 2004 Stilo 1.4 that's done 145k. Until recently it was averaging 40mph, then for a week or so I noticed the car needed the accelerator pressed further to get the revs. and speed up through the gears. I also had a feeling I was using more petrol, so I scrolled through the indicators to average consumption and was shocked to see it had dropped to a measly 31mpg. .

A few days after this the yellow dashboard light came on and stayed on, so I used a cheapo. meter thing off Ebay to find the fault code(s). There were three:

P0130 O2 Sensor Circuit Malfunction (Bank 1 Sensor 1)
P0505 Idle Control System Malfunction
and
P1172, which I can't find on the error code list. Maybe because the Stilo 1.4 has a Punto engine.

I cleared the errors and the warning light has not come back on. The car doesn't have any misfires, the revs. are steady when idling and it drives smoothly once it consents to reach 30mph+, so it's still getting me from A to B in reasonable comfort, but losing 10mpg is becoming expensive.

I'm not sure what is causing the fuel economy problem. I presume the first is a Lambda sensor, which is annoying as the cat. and the sensors were replaced less than 18 months ago, but I'd rather not go spending money getting this fixed if the other codes indicate other expensive things that need replacing. After all, the car is only worth a few hundred quid, so you have to draw the line eventually.

Any ideas? Thanks.

Greetings Cambelt....

The P1172 I believe is a fuel trim related code. Its got a couple of potential meanings for Fiat so far as I can tell but they relate to the long term and short term fueling trims - which would add up if you're experiencing greater consumption and lambda issues.

You obviously have detected a lambda sensor code here too.

You could do with getting it on a good diagnostic setup to see whether or not the lambda sensor is showing any oscillation or not to know whether the lambda is working. You should be aware that lambda sensors do not frequently give EML (engine management light) on the dash, so the fault could be there are you not be alerted to it. The fault code may also be cached, so it could be a historic code not currently detected. You've done right by clearing codes and waiting to see what comes back - but monitor for new codes even if you don't get EML.

What you need to remember here is that the car is telling you there is something wrong at the lambda - not something wrong with the lambda.

The sensor may well be working perfectly but the readings it is seeing from the sensor lead the car to believe there is a problem. With it being a fueling trim issue (i.e. mixture being out) it could potentially be a MAF issue, although I tend to know MAFs fail to lean rather than rich.

Note that the P code you got is a manufacturer specific code so generic code readers can sometimes misread them and certainly won't know the fault description.

If you want more diagnostic capability investigation Multi ECU Scan (software) and an ELM or KKL cable. MES as the software is know supports a number of ECUs for free - check the website to see, or if your ECU is included in the registered version its 50 euros I think for a subscription.

Many thanks for taking the time to reply so fully.

I forgot to mention when I first tried to self-diagnose, I did speculatively change the MAP myself a few weeks ago, which was easy enough for someone as simple as me, but it made no difference, which isn't really surprising given that code wasn't flagged up. I then went looking for other fuel related bits that might be a problem and got confused as to whether the Stilo has a MAF, or just a MAP. Some cars have this big filter thing that needs cleaning, but I don't think the Stilo/Punto has one. Perhaps you can enlighten me.

Based on what you say, it may well be that the lambda code dates back to the time just before I had to have them and the cat. replaced, and not acfresh fault which would be some good news.

It's also occured to me after reading your post, that the problem could be the ECU itself. Would it be easier just to replace the ECU, or does that create another load of problems such as the transponder not working? I can buy a 2nd hand ECU off Ebay for £20, but according to another thread on this forum, it's useless unless it's been wiped clean of data. That's assuming it's not faulty as they're all 12 years old. It seems they're prone to the connector pins dropping and disconnecting internally, but they can be soldered back into place.

I expect a brand new ECU costs more than the car is worth! And the software you mention doesn't fix a faulty ECU.... I dunno what to do for the best