Hello.

A week ago I purchased a 2015 mk3 facelift focus estate 1.0

Car has done 2000000km but was sold with warranty, service history, lots of new parts including new belt and water pump.

But unfortunately the check engine light came on 2 days after I purchased the car.

So I brought the car back to the dealer and he replaced the pre cat 02 sensor.

1 day later the check engine light came on again. The dealer says the error (p0420 cat efficiency low) might appear because the new sensor needs coding?

This sounds strange to me so I used forscan to look at various values and noticed the increase to 53° at 2500rpm.

Is this normal or a symptom of a problem beside the bad cat ?

I really enjoy driving this car but bringing this car to and from the dealer is very inconvenient for me so I would really appreciate suggestions for what I can do with my limited toolkit and forscan to access if this car is worth keeping or if I should push for a return....

53° spark advance at 2500rpm is not automatically a red flag on these engines. On a low engine load condition, modern turbocharged petrol engines can run very high ignition advance because cylinder pressure is low and the mixture burns slower. The important thing is engine load.

Personally, I wouldn’t panic over the 53° timing figure.


The P0420 DTC code will almost certainly be caused by a worn catalytic converter that simply lost part of its efficiency. This is quite a common problem on the 1.0 EcoBoost. What is worrying is that the dealership is saying that the O2 sensor may need coding. Everyone knows that this is just a sensor and no coding or programming is involved whatsoever.

When the catalytic converter is going to be replaced you should insist that a new original one is installed. Aftermarket catalytic converters are a lot cheaper but also contain a lot fewer precious metals (platinum, palladium, rhodium). These wear out even faster. It is quite common for an aftermarket catalytic converter to cause the P0420 DTC code within a Year due to lost efficiency.


You say the car has done 2.000.000 KM. I assume you typed a zero too much and actually mean 200.000 KM?

You say that many parts were changed but do not specify which parts. The wetbelts (2-Pcs) and waterpump are just scheduled maintenance parts. At this age and mileage there are lots of parts that can be expected to require replacement at some point. For example:

- Turbocharger
- High pressure fuel pump
- Vacuum pump
- Engine mounts
- EPAS steering rack
- Exhaust system
- Suspension parts (varying from bushes to complete suspension arms)
- Clutch
- Flywheel

3 hours ago, JW1982 said:

53° spark advance at 2500rpm is not automatically a red flag on these engines. On a low engine load condition, modern turbocharged petrol engines can run very high ignition advance because cylinder pressure is low and the mixture burns slower. The important thing is engine load.

Personally, I wouldn’t panic over the 53° timing figure.

Google seems to agree with you. So thats great 👍


The P0420 DTC code will almost certainly be caused by a worn catalytic converter that simply lost part of its efficiency. This is quite a common problem on the 1.0 EcoBoost. What is worrying is that the dealership is saying that the O2 sensor may need coding. Everyone knows that this is just a sensor and no coding or programming is involved whatsoever.

Yes I don't trust this dealer as I'm pretty sure he knew about the p0420 error before he sold me the car. But sofar I'm being polite as I don't think playing hard ball will get me anywhere. I am member of our nation motorist organization so their free legal advice will be my last resort. But I'm hoping to avoid having to go that far...

When the catalytic converter is going to be replaced you should insist that a new original one is installed. Aftermarket catalytic converters are a lot cheaper but also contain a lot fewer precious metals (platinum, palladium, rhodium). These wear out even faster. It is quite common for an aftermarket catalytic converter to cause the P0420 DTC code within a Year due to lost efficiency.

As the car has done 195.000km and is 11 years old I don't think I can demand the cat to be replaced with a new original... So would a used ford cat be preferred vs. a cheap new aftermarket cat?


You say the car has done 2.000.000 KM. I assume you typed a zero too much and actually mean 200.000 KM?

Actually 195.000km.

You say that many parts were changed but do not specify which parts. The wetbelts (2-Pcs) and waterpump are just scheduled maintenance parts. At this age and mileage there are lots of parts that can be expected to require replacement at some point. For example:

- Turbocharger
- High pressure fuel pump
- Vacuum pump

Vacuum pump and rear brake discs was replaced 3 years ago at 156.500km.

- Engine mounts
- EPAS steering rack
- Exhaust system

Rear exhaust and muffler was replaced 3 years ago at 183.000km. It doesn't look bad.

- Suspension parts (varying from bushes to complete suspension arms)

Rear shocks was replaced 4 years ago at 136.000km

- Clutch
- Flywheel

3 hours ago, JW1982 said:

I realize some things will break sooner or later...

For my daily commute I drive a corporate van so usually only drive my private car about 5-10.000km a year during weekends and holidays.

In my country annual "car owner tax" cost about 100€ for petrol cars that officialy does >20km/l. But it's progressive so a car that only does >11km/l cost 1000€ -and our governments has a habit increasing this tax every year!

As I don't want to borrow money for a car my options was either a high milage car with history and warranty or a slightly less used car without warranty and/or history.

As the 6 month warranty isn't distance limited I will try to do extra kms in this period and give the car a good thorough test 🤞