I've had a look round but can't really see an answer, so hopefully someone will know a bit about the EML faults.

My 2007 Panda 1.2 4x4 threw the engine management light on without warning. It came on while trundling about at the zoo, and stayed on. No symptoms, engine running fine, no misfiring, no loss of "power", or increase in fuel consumption.

Local garage tried their generic tester as the Fiat dealer couldn't help this week(!), and it read "P0172 unknown fault". It then reset the light successfully and so far (only a day) it's stayed out. Does this code mean anything to anyone?

The battery had been flat after 2.5 months of standing, and the car had been idling oddly (revs rising and falling) starting from warm a few times. This had resolved itself before the EML came on though - connected?

The Panda has been throwing a flashing EML on motorway runs when it's working hard - this goes away again if you ease off. I'd put it down to the 113k on the clock & maybe a sooted up sensor or something (the handbook suggests a flashing light may be emissions related). A long motorway incline is most likely to trigger a flashing light.

Are these likely to be related, and is there anything likely to be causing it? I don't want to damage the car & it runs so well I don't think there's anything seriously amiss. It's a bit annoying (on its rare long trips) to have to keep backing off, when it clearly feels happy at higher speeds.

Any thoughts from the forum gurus would be welcomed.

P0172 Basically means that the O2 sensor has detected a rich condition which it can no longer trim out it's self.

The upstream/pre cat O2 sensor trims the fueling after the car/sensor has warmed up.

To do this is works in a different way to most sensors and has two parts to it.
A heater
So it'll take voltage to pre heat it's self so it can work quickier.

And the sensor.
This actually generates a small electrical charge via the heat of the exhaust. (between 0.1v and 0.9v)
Hotter = lean and a slightly higher voltage is produced
Cooler = rich and a slighty lower voltage is produced.

When running correctly these reading will swing or switch back and forth every second or so, but the mid point average will be 0.45v, this indicates perfect fueling.
It does this by adding and removing fuel by altering the bandwidth of the injection and thus knocks the exhaust temp/O2 sensor voltage back and forth. (Closed Loop)

Your ECU has detected an average trim that suggests it's running rich or/and can no longer trim the fueling correctly.


There are various things that can go wrong and it isn't always straightforward.

But 9 times out of 10 it will be a fault with the O2 sensor, either it's sensor has degraded or more likely the heater element is failing and it can't get out of it's warmup cycle ("Open Loop") which is also very rich (like pulling the choke on on an old car) as it can't detect a reliable "hot" signal from the O2.

This second one I've suffered with (exact same rise and fall of the rpm) and it will cause the car to run in an "Open Loop - system fault" fuel setting which is very rich to protect the engine for over heating, but the sensor will eventually heat up just from the exhaust gas after being driven a while.

You can usually stop and restart the car after a short pause when it's warmed up and it will run ok as the O2 is now hot enough to work correctly, that is until the O2 cools off again!

I seem to recall the second sensor, the downstream/post cat one is the same sensor as the precat one and as the post cat one does not effect fueling trim, you could try swapping them over.

All the post cat one does it monitor the cat efficiency and seeing as this alters with the cats temp, it can read almost anything (within reason!)
A fault with this post cat sensor isn't going to effect running, but at worst flag up a cat efficiency DTC, but at least you'll know you've isolated the problem.

There are some other things that can cause this issue, some of which are confusing but rare, but this is where I'd start.

Thanks for that. If it comes back, that will help enormously in tracking the problem down.

If it continues to flash on my odd longer motorway journeys, can that actually cause any harm? I slow down & it goes away, but is that ok, or does it need investigating?

Its very broken Gavin, and very expensive to fix, making the car nearly worthless, I'll give you £300 for it though :devil:

Most Easterly Pandas said:

Its very broken Gavin, and very expensive to fix, making the car nearly worthless, I'll give you £300 for it though :devil:

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Thanks Jon - that's a big weight off my mind - you're too generous for your own good sometimes!