Replacing O2/lambda Sensor 2.3

[Stevoo]

I will be changing my o2/lambda sensor due to error code(p0171) on ecu along with power loss, low mpg and missfiring.

My question is regarding the cable connector end, i hear its not easy finding the plug in the engine bay to remove. Most ppl cut the wire and tape it up with electrical tape.

 

Anyone got any input pls?

[sepulchrave]

It should be easy enough to find from under the car if you follow the cable from the lambda probe.

 

Get a new one but don't bother with the cheap universal probes, yours is probably a 4-wire type with heating element.

 

It shouldn't be difficult to remove if you have a crowsfoot spanner the correct size (22mm?).

 

The new one should come with thread sealant already on it, don't be tempted to use anything else, the fumes can kill a new probe.

[Stevoo]

yer its 4 wire. thanks for help.

[marcr]

I've recently developed a misfire on my sharan along with (even more) shockingly poor mpg. How does a faulty lambda probe cause this?

I was going to start with leads and plugs but now i'm wondering if that would be the best start? In an ideal world i'd have new plugs, leads, coilpack, MAF and lambda sensor but i'm on a budget with the school hols starting.

 

First step is a VAG-COM lead i guess?? Any recommendations??

thanks.

[sepulchrave]

A faulty Lambda probe 'lies' to the Motronic ECU about the combustion efficiency of the engine.

 

Motronic is totally reliant on closed loop Lambda feedback for all it's fuelling information, it uses this information to write a dynamic correction table which contains all the information about how your engines fuelling needs differ from the base or default map.

If this correction table is corrupted by incorrect data due to a faulty Lambda reading then the dynamic map actually becomes worse than the base map.

 

To check this, don't bother with VAG-COM (but you might as well get the cheap lead off ebay for

[marcr]

I've had a quick look at the ht leads and one has damaged rubber near the coilpack boot. I think i ought to change them so that i can hopefully fix the misfire. If nothing else i can eliminate them. Have seen them for about

[sepulchrave]

The Lambda probe is under the car, below the gearchange mechanism approximately and is easy to get at when the car is raised at the front.

[acombe]

NGK Iridiums ? are they the same as Platinums !!!

[marcr]

To check this, don't bother with VAG-COM (but you might as well get the cheap lead off ebay for

[marcr]

when you fit a new probe you should reset the ECU by disconnecting the battery and shorting the leads together.

 

Does this literally just mean taking both cables of the terminals and touching them together then refitting?

[sepulchrave]

when you fit a new probe you should reset the ECU by disconnecting the battery and shorting the leads together.

 

Does this literally just mean taking both cables of the terminals and touching them together then refitting?

 

Yes, hold them together for a few seconds.

[marcr]

Many thanks for the input. I'll let you know how get on. How did you got on Stevoo?? Did it fix it?

[Stevoo]

yes and no mate, see my new post, still got no pwer over 3000rpm but much better mpg!!

[marcr]

I've changed the O2 sensor. It was relatively easy to do with the front of the car driven up onto ramps. The probe was mounted outside of the undertray just before the cat so had pretty good access.

I only managed to get a universal one in time for the weekend when i needed the car but it seems to be have done the job. Nice, smooth power delivery again and good mpg for

[Stevoo]

well done marc, luckly my car doesnt come with the under tray, so only took me 20 mins to remove and replace the probe.

 

I have a feeling that my cat which is a pattern part one(replaced 2 years ago by previous owner) is causing the problem. its the only part which doesnt have a sensor to say its not working :lol: