Air-Fuel Ratio - Engine Management warning

[monkey64]

I've got an 09 Jazz which has done 99k. 

A couple of days ago the engine management light came on and the local garage diagnosed the code as 'Air-Fuel Ratio'. Now the car runs fine and the fuel economy hasn't changed.  They said they had seen similar issues on other cars and thought it might be something to do with the E10 Petrol I'm running it on.  They recommended 2 possible routes to go down:

1. Replace both Lamda sensors as they can't tell which one is cauding the problem.  Likely to cost £480 but could be more if they damage the exhaust system.
2. Run the tank down, fill up with E5 next time and add some 'Cataclean' which may clean the O2 sensors.

Given the age of the car I don't want to spend big money on it.  I can see O2 sensors available quite cheaply on eBay and mine are the original ones which came with the car.

What would you do / any ideas?

[olduser1]

This link although USA have useful info
https://www.fitfreak.net/forums/2nd-generation-ge-08-13/97927-help-oxygen-sensor-problem.html

[embee]

My MOT chap commented that some relatively modern cars have been flagging faults when using E10 due to the slightly greater shift/offset in feedback in order to maintain stoichiometric fuelling. He said there have been a couple of examples where there have been no actual faults found but reverting to E5 had stopped the issue. I don't know what specific vehicles he had seen, but apparently several MOT testers had observed/reported the same issue.

The ECU programming will have included a specified range of fuelling correction considered to be within bounds expected, if the extra oxygenated fuel causes the shift to be outside this range it will flag a fault, even though there isn't any "fault" as such, just operating outside a set limit.

At least trying out the "E5 fix" is a relatively cheap exercise (it's just the oncost of E5 vs E10 which is only a couple of ££ per tank if you want to try it).

I don't know whether this has been verified independently.

[CRC]

There are two lambda sensors on the Jazz. Although they are known as lambda sensors, they are in fact measuring oxygen in the exhaust gas.

Lambda is a ratio and at a value of 1, the combustion is at a perfect stoichiometric ratio, in other words perfect combustion. Below 1, combustion is rich, and above 1 combustion is lean.

The pre-cat sensor is used by the ECU to determine how much fuel to inject into the engines, and the post cat sensor determines if the cat is working efficiently or not.

Any half decent OBD reader will show the values from the two sensors, and normally, the pre-cat one will be oscillating between rich and lean quite rapidly, while the post cat sensor will show a much smaller variation as the cat smooths out the oxygen reading.

Bosch sensors are about £40 each and provided they unscrew OK, they should take about half an hour to change with the benefit of a two poster lift ....

£480 is having a laugh .....

[MiniNinjaRob]

£480 is a joke. They take 5 mins to fit, normally one spanner to remove and plug at other end into electrical system.
If they think they would damage the exhaust I would never use them to work on my car, what a bunch of cowboys.
Infuriates me that the car industry acts like this.

[Major clanger]

We have a 2014 Jazz that we run on E40, any more than that and it trips an engine light.  It is not especially tolerant of Ethanol like my Ford which can go to 70% E85 added without issue but I very much doubt E10 would cause this problem.

First thing I would do is check the Long Term Fuel Trim Figure.  Most cars trip the engine light at about +/- 20 to 25, see what it is showing.  The other thing you could do is log the O2 sensor and go for a drive, its a wideband so the figure should be relatively stable at 1 during the drive.

[monkey64]

NOW FIXED

I bought an OBD2 code reader and it gave me a P0135 code which refers to a heating element issue of the oxygen sensor (pre Cat).

Bought a replacement 'Kavo' brand from Autodoc but the plug was nothing like the original (not even close).  Did think about de-pinning and using the old connector but the part did not seem correct at all.  I think it's a very poor cheap chinese copy.  Lesson learned!  Returning goods to Autodic in Germany was a night mare because the parcel got stuck in customs!

In the end I bought the correct Denso part and the car has worked perfectly ever since.  it's not a hard job to replace the pre Cat sensor with a breaker bar and an O2 socket. 

Thanks to everyone who posted.

[olduser1]

Good to learn how you solved this matter, those parts from China are  best avoided.

[MiniNinjaRob]

Well done! The way I see it is that you are saving a tonne of money doing the work yourself so buying an OEM or quality branded item is still way cheaper than paying a garage to supply and fit it. Even if you have to buy the tools as well!
Hence why I always use Honda parts or top quality branded stuff. I did the same on my last car - a Volvo - and never had an issue.