Hi all

Being an elderly gentleman, I haven't been a  great forum user, but have decided to give it a try - hope that's OK with everyone.

We recently bought a MK4 20 plate 1.0 Ecoboost  (non MHEV) for my wife.  It’s low mileage (28k) and with full Ford service history.  It appears very well looked after. 

Unfortunately we have had the engine management light come on with a code P2096 Post Catalyst Fuel Trim System Too Lean (Bank 1) (I have a basic code reader). The car seems to be running fine, no loss of power, fuel consumption good, nothing to suggest a problem.   I’ve had the car in at my local garage (who I have used for decades on over 8 different cars) and they have said it’s difficult to track these things down, especially when the car shows no other symptoms.  After checking ot over and running diagnostics, they suggested changing the Post Cat sensor, which sounded a sensible first step.  They’ve done that, and after a few days the light came back on with the same code. Before spending any more at the garage I’ve tried to educate myself a bit more.  Go easy on me, I’m new to a lot of this, but willing to learn.

I did a bit of reading / research including this site and decided to join and see if anyone can offer any guidance.  I’ve recorded the freeze frame data from both times the light came on (before and after new sensor), and they are generally similar.  The thing that did catch my attention was the fuel trim figures, with the short trim looking OK (+/- 3%) and the long trim showing +20-25%.   So I did more reading, and collected some live data, and have some questions.

The short trim is now showing at + 20-25% when at idle (warmed up, cat temperature above 500 d c . ) The long trim is currently low, below 5%, I guess this is all due to the very recent reset of data.  When we drive the car normally and I can monitor the data, the short trim is pretty much normal, around 0 +/-   3 %.  But when we stop at junctions etc, it goes back up to 20-25% .   Research suggests possibly a small vacuum leak at low rpm ?   This would tie in with the mpg being unaffected?

Under the bonnet looks very, very clean and well maintained, and I can see not obvious connections or hoses that look disturbed or damaged.  The exhaust and cat look undamaged.  All wiring looks clean and undisturbed. I’m aware of smoke tests etc, but given the low mileage and the ‘looked after’ feel of the car, wouldn’t it would seem odd to have a leak due to a fault / damage?

The replacement sensor was a Bosch, so I think decent quality. 

Looking at the history, there’s a decent chance the car was previously used for short journeys.  Currently its been used for 5-10 mile daily journeys, with the occasional long run (>100 miles) perhaps every couple of months.  Does that add any clues?

I’m not sure of the next step.  The mechanic has hinted at possibly the upstream sensor next, but he is open on this being a process of elimination, trying to pick the lowest cost options first.  I wondered if some Focus owners would be able to contribute some input that might help?

Thanks for reading – any and all help appreciated

Cheers,  Bill

Hi Bill, welcome to the forum.

As no-one has jumped in on this yet I'll offer my six-pen'north. The gurus on here generally recommend the use of FORScan for reading codes. It's a free download for a Windows laptop and only needs a suitable cable costing about £30. There's also a paid version for smart phones which also need a bluetooth dongle.

Ford cars have two separate CAN data buses, a high-speed and a medium-speed. General-purpose code readers as used by the majority of non-Ford garages, can only read the high-speed bus and read generic DTCs so can't access the many Ford-specific codes which might give additional clues to the nature of your problem.

@unofix is your go-to man for this:

FORScan (for use with Windows Laptop) : https://forscan.org/download.html

It's what many Ford owners use including some Ford technicians.

• vLinker FS, cable for laptop: https://www.amazon.co.uk/Vgate-vLinker-Adapter-FORScan-MS-CAN/dp/B0952P4MLP

Hi,

As @mjt says, absolutely use FORScan to get a full idea of the codes.

BUT!

I reckon, change the spark plugs, fill the tank with E5 or E0 Super unleaded (I recommend Tesco as it's 99RON and cheaper), stick a bottle of cataclean in, give it some welly and see how you get on.

Especially as you've changed the sensor already.

It could be something else, which FORScan may help you with, but I doubt it

Spark plugs should have been changed last year at the 4th year service with full Ford history.  Worth checking that before replacing them as they're expensive on these.

Lean mix after the cat doesn't sound like poor combustion to be though.  Sounds more like a small rust hole around the cat that's sucking in some fresh air to pass the 2nd lambda.

Cataclean is definitely worth a try as well though.  If the cat is dirty, it won't be able to add oxygen to carbon monoxide effectively, leaving that oxygen 'spare' after the cat.

Some very good suggestions above.

My first thought is the car needs a decent run out, at least 30 miles, more if you can. It's not about blasting down a motorway at 70+++  what you need is a steady drive at 50 to 60 mph and if your car is manual drive it in a lower gear (and if it's an auto, select sports mode), so for the whole of the journey don't use top gear. The name of the game is to keep the revs up a bit and get the engine and exhaust nice and hot.

Before beginning your 'test run' it would be a good idea to do as Dave suggests and fill up with good quality E5 fuel and also add a bottle of catclean.  These problems are common with cars that have spent most of their life doing short runs and never properly getting fully up to temperature.

As mentioned, the correct diagnostic programme to use with this car is FORScan. Either the windows laptop version or one of the mobile phone versions. They can all read the exact same Ford specific DTC's.

On 4/7/2024 at 8:59 PM, unofix said:

FORScan (for use with Windows Laptop) : https://forscan.org/download.html

It's what many Ford owners use including some Ford technicians.

• vLinker FS, cable for laptop: https://www.amazon.co.uk/Vgate-vLinker-Adapter-FORScan-MS-CAN/dp/B0952P4MLP

OR

• OBDLINK EX, cable for laptop: https://www.amazon.co.uk/OBDLINK-EX-FORScan-OBD-Adapter/dp/B081VQVD3F/ref=sr_1_5

For diagnostic use only:

• vLinker FD, for android phone: https://www.amazon.co.uk/Vgate-Bluetooth-vLinker-Scanner-Diagnostic/dp/B08H82WC8L
• vLinker FD+, for iPhone: https://www.amazon.co.uk/Vgate-Bluetooth-vLinker-Scanner-Diagnostic/dp/B08H8JHWP2

 

Hi guys, many thanks for the welcome and the helpful replies.

All major services have been at Ford, within the mileage specs, and also two intermediate services at Ford as well.  The invoices say the plugs have been changed.  

Its had a couple of very long runs (150 miles mainly motorway) before the problem started, in fact the first time the light came on was during one of those runs.  But those runs probably didn't use high revs, more cruising in 6th gear.  I get the idea behind getting things properly hot.

Thanks for the FORScan links.  I had been using a basic code reader as i didn't want to risk altering anything.   Is Cataclean safe to use with these engines? I've always shyed away from additives, although I had been thinking of trying super unleaded to see if it made any difference.  

The cat explanation is really helpful, thanks.  I couldn't visualise how a dirty cat (possible with the low mileage) could give a lean reading on the post cat sensor.

There's something else I wanted to ask.  The engine, to me, seems to run very smoothly, no hesitation and plenty of smooth power.  However, at idle, when i lift the bonnet, it does seem to vibrate at tickover a bit more than I expected.  At 2000rpm its very smooth. I have assumed that's the nature of a 3 cylinder engine?

Anyway, thanks for the feedback guys. I've reset the EML and it took around a week or so for the EML to trigger after the last reset, so i can try the E5 fuel and getting the cat and exhaust properly hot in the meantime.  Cheers,  Bill

 

Hi All, just wanted to post back on how this worked out (and to say thanks for the help)

So, I followed the suggestions, put in 1/2 a tank of Super Unleaded (E5), gave it couple of decent runs keeping the revs up a bit (as recommended to get it properly hot) with my wife using it for normal day to day use between those runs. When down to just under 1/4 tank of petrol I got a bottle of Cataclean from Halfords, added it to the remaining fuel, and did a couple more of the same runs, again with normal day to day use in between. When the fuel light eventually came on, I filled up with E5 again and the car was soon after used for a long motorway trip.  Since then it's been OK, no EML or codes, its been around 4 weeks now.

Anyway, I reckon its cleared the problem, and it seems to make sense to me _why_ its cleared, so thanks again guys.  I just wanted to post back in case the info is useful to anyone else. - Cheers

2 hours ago, Bill_S3 said:

Since then it's been OK, no EML or codes, its been around 4 weeks now.

Who doesn't love a happy ending ? 🎉🎉🎉

On 10/6/2025 at 8:03 PM, Bill_S3 said:

There's something else I wanted to ask.  The engine, to me, seems to run very smoothly, no hesitation and plenty of smooth power.  However, at idle, when i lift the bonnet, it does seem to vibrate at tickover a bit more than I expected.  At 2000rpm its very smooth. I have assumed that's the nature of a 3 cylinder engine?

Glad to see the "Italian tune up" seemed to do the trick. 

As no-one seems to have picked up the point above, I'd say it was pretty normal.  My previous 1.0 Fiesta, in particular, felt and sounded very smooth from within the car. Stand outside and lift the bonnet and compared to previous 4 cylinder cars, it sounded like a bag of spanners and the engine leapt about as if it was making a bid for freedom!