O2 Sensor Problem

[JoshEv]

Hello everyone,

Recently I've been having an issue with my Ford Focus Mk2 (2005) Petrol. I'll give a short description of what is happening and see if any of you know what might be causing the issue.

So about 3 weeks ago I noticed the engine warning light come on so I took it to a garage which my normal one recommended since they were over booked. They said they ran some tests and it showed up that the o2 sensor was faulty so they replaced it with "top quality parts", which cost me £181 all together including labor.

Exactly 1 week later, on the way home from work I saw the light pop on again. This time I plugged in a OBD2 self diagnostic tool and the code p0156 came up and after reading online it suggests that the o2 sensor is faulty. So I took my car back to the garage and explained to them that the light came back on and that code came up saying the sensor is faulty. After leaving my car with them for the day I had to ring them up and ask them what the deal is. The owner of the garage then told me my battery was running at 25% capacity and it needed replacing. So that same day I bought a new battery and replaced it.

Exactly 1 week later again the light comes back on! I plug in the OBD2 tool and the same code appears, p0156. Getting rather annoyed I rand up the garage and told them that after spending £181 the week before and buying a new battery the light came back on and the same code came back up. They told me to bring the car back down to them and they'd sort the problem out... So I did. Once again after leaving my car with them for the day I had to ring them up and ask what was happening, one of the mechanics said to me that they had just finished fitting "a part" and that I could pick up the car if I needed it but ideally they'd like to keep it overnight so they could test it in the morning when it was colder. I didn't desperately need my car so I agreed to leave it with them over night. The next day I phoned them up about lunch time and the owner answered. He said they can't find out what is causing the issue so they will run more tests and they'd let me know by the end of the day.

It got to the end of the day and I hadn't heard anything from them... I didn't phone them because I didn't desperately need the car and I didn't want to rush them and be annoying. A day later they phoned me and said the car is ready to be picked up and that the first sensor they fitted was faulty and replaced it under warranty so I didn't have to pay anything. Great! I thought, no longer will this issue come up. Until this morning... When I started up my car and left it running for 5 minutes to warm up I noticed the light pop on once again.

Instead of calling the garage I decided to come on here and see if anyone else would know what might be causing the problem?

Thanks in advance,

Josh.

[south_bound]

I had the red dash light and a similar code come up about a year ago and the garage quoted me a similar price to replace the sensor (I think the O2 is also sometimes called the Lambda sensor?). I had a lot going on at the time and didn't get around to booking it in so just kept running around with the dash light intermittent at first and then becoming permanently on. I kept this up for a good few months and then the "engine systems failure" so I had to do something. Are you noticing anything else in the way the car drives - mine was a bit lumpy with poor mpg, but that is more likely liniked to a clogged dpf.

I eventually deleted the dpf which disables these sensors and the problems have gone away and all good since. There are good reasons to not go down that route any more, but what might be interesting to you is that when the dpf was removed, the tech found that the rubber hoses leading to the O2 sensors were burned through at the point they connect to the front of the engine block. The sensors were therefore not reading anything meaningful and maybe that was causing them to send out an error code. It might be worth you chjecking this yourself before shelling out for new sensors.as they are pennies to replace. Hope this helps, let us know how you get on.

[JoshEv]

Are you noticing anything else in the way the car drives - mine was a bit lumpy with poor mpg, but that is more likely liniked to a clogged dpf.

I know a faulty o2/lambda sensor does effect the MPG which it has been doing and sometimes the car does feel a bit lumpy.

I eventually deleted the dpf which disables these sensors and the problems have gone away and all good since. There are good reasons to not go down that route any more, but what might be interesting to you is that when the dpf was removed, the tech found that the rubber hoses leading to the O2 sensors were burned through at the point they connect to the front of the engine block. The sensors were therefore not reading anything meaningful and maybe that was causing them to send out an error code. It might be worth you chjecking this yourself before shelling out for new sensors.as they are pennies to replace. Hope this helps, let us know how you get on.

Forgot to mention that mine is petrol so unfortunately I don't think this will be much help. But thanks anyway.

[south_bound]

Forgot to mention that mine is petrol so unfortunately I don't think this will be much help. But thanks anyway.

OK, I missed that part in the original post.

[wase16ll]

unfortunately, its not a code that can be diagnosed over the www.

the code is referring to a heater circuit malfunction on the after cat sensor

the heating circuit is fused, but this is unlikely to be a fuse issue as it shares the same fuse as the pre cat sensor, though it may be a wiring problem somewhere between the fuse and the sensor as the sensors run seperate wires from the fusebox

it may be a poor quality sensor (if heater circuit shorts out within the sensor then nothing you can do bar renew the sensor)

it may be a poor earth on the sensor

it may be a poor connection, due to getting bathed in puddles over recent months (seen a lot of this recently)

heater circuit is fairly straightforward to test, so would suggest you ask the garage exactly what is occuring as they have obviously carried out tests on it...its either receiving the correct voltages etc or not..if getting the right voltages, then has to be a connection or sensor issue..if it isnt, then connection/wiring/ecu problem

[CharlesW]

My O2 sensor was changed when the Engine Management light came (steady), this was only 2 weeks ago. Last Friday took it back to garage, who stated that the O2 sensor is faulty again. Fortunately it’s under warranty, so it won’t cost me other than inconvenience of keep going to garage.