O2 sensors codes after manifold removal - what should I check first

[penant78]

Hi,

I recently removed the exhaust manifold of my 2006 2.0 as it had the usual crack and needed a small welding.
After that, the engine light came and I had codes 2c45 and 2c9d which refers to the pre cat sensors.
I refitted everything correctly (already done that on another 2.0).
I erased the codes but they came back shortly.
Today I went to the technical control (belgian MOT)
And the car did not pass the emissions test.
It is obviously related, but should I check that I refit the plugs correctly, is it possible that a bad connection throw a code, or should I directly look for replacement sensors?
Thanks for your help.

 

[ph001]

Replace pre-cat o2 sensors

 

[Jfgoldfish]

Replacing the sensors is a sensible move if the car has covered 100k or more. They get quite slow as they age. The leaking manifold causing poor fueling won't have helped.

The codes and failed emisions could be due to wacky fuel trims from the leaking manifold. It would be a good idea to reset them. Otherwise they will still sort themselves out after awhile.

A basic code reader that can show live data will very easily tell you if the sensors are functioning correctly.

 

[penant78]

Replacing the sensors is a sensible move if the car has covered 100k or more. They get quite slow as they age. The leaking manifold causing poor fueling won't have helped.

The codes and failed emisions could be due to wacky fuel trims from the leaking manifold. It would be a good idea to reset them. Otherwise they will still sort themselves out after awhile.

A basic code reader that can show live data will very easily tell you if the sensors are functioning correctly.

I have INPA that allows me to read codes and I know I could have live data from the sensors, but need to be sure of what I do.
Any link for that?

 

[Jfgoldfish]

Any link for that?

I can't remember the exact menu structure off the top of my head. I can probably plug my laptop in later and let you know.
There is really very little chance of doing something silly with INPA. I would suggest flicking through all the options and familiarising yourself with the data available.

When trouble shooting O2 sensors:

Check the sensor heaters come on from a cold start.

Let the car heat up and check that both precat sensors are producing a similar voltage. I believe that should be around 0.7ish volts.

Rev the engine and check that the value changes.
As the revs drop (during deceleration) the O2 sensors voltage should drop to nearly zero before picking back up.

Reset the adaptations after doing major works such as precat exhaust leak repair.
The fuel trims should be available in INPA. My bet would be that they are quite high. Has your consumption been a little poor?

 

[penant78]

The code came after the cracked manifold and I erased it.
I went for a short run (6-7 miles) yesterday and it did not came back.

 

[Jfgoldfish]

I went for a short run (6-7 miles) yesterday and it did not came back.

In that case I would assume the codes were a symptom of the cracked manifold and not failed O2 sensors.
The fact that the car failed emisions is an issue though. Do they plug the car in via OBD to check emisions? If they do, you will need to complete a full 'drive cycle' without emissions related codes popping up before it will pass.

 

[penant78]

I went for a short run (6-7 miles) yesterday and it did not came back.

In that case I would assume the codes were a symptom of the cracked manifold and not failed O2 sensors.
The fact that the car failed emisions is an issue though. Do they plug the car in via OBD to check emisions? If they do, you will need to complete a full 'drive cycle' without emissions related codes popping up before it will pass.

No, they just put a probe in the exhaust back box, linked to their computer

 

[colb]

Always best to insist they test the emmissions when the engine is very hot, ensure your plugs and air filter are in good order as well.