New oxygen sensors and still 171 code

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Jul 31, 2014 | 11:17 AM

Henry Bosch

Thread Starter

Newbie

Joined: Jul 2014

Posts: 7

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From: Johannesburg

2005 C230K Coupe

New oxygen sensors and still 171 code

Hi all

I have recently replaced a lot of parts on the C230.

2005 C230K Coupe
M271

Here is a list:

1 - All breather pipes, (even under the supercharger)
2 - Cam magnets and the harness.
3 - Maff ( Not Original)
4 - Upstream Oxygen sensor(Original)
5 - Downstream Oxygen sensor(Original)

My problems are as folow:

1-Even after replacing everything I still get a 171 code( System Too Lean Bank 1)

2-My upstream oxygen sensor has a voltage of 1.508v and sometimes changes to 1v or 0.980v

3-Short term fuel trim runs on 0% and sometimes runs into negative

4-Long term fuel trim stays at 25% and does not even move

Is my ECU stuffed? or is there something I am missing?

Jul 31, 2014 | 11:27 AM

BigN8

Junior Member

Joined: Sep 2013

Posts: 65

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From: Coon Rapids MN

2005 C240

My bet is a vacuum leak.

double and triple check all hoses

Jul 31, 2014 | 11:49 AM

Henry Bosch

Thread Starter

Newbie

Joined: Jul 2014

Posts: 7

Likes: 0

From: Johannesburg

2005 C230K Coupe

Quote:

Originally Posted by BigN8

My bet is a vacuum leak.

double and triple check all hoses

No vacuum leaks, checked all.

Jul 31, 2014 | 02:40 PM

VVF

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Joined: Sep 2011

Posts: 1,657

Likes: 35

From: Austin, TX

2005 C230K(sold), Mk7 Jetta

Non-original MAF sensor is suspicious. I am not sure aftermarket ones work on these engines.

Jul 31, 2014 | 03:17 PM

BigN8

Junior Member

Joined: Sep 2013

Posts: 65

Likes: 0

From: Coon Rapids MN

2005 C240

That is my second guess also. MAFs are not all equal.

Aug 1, 2014 | 03:06 AM

Henry Bosch

Thread Starter

Newbie

Joined: Jul 2014

Posts: 7

Likes: 0

From: Johannesburg

2005 C230K Coupe

Quote:

Originally Posted by VVF

Non-original MAF sensor is suspicious. I am not sure aftermarket ones work on these engines.

That is true, but even when car is not running the reading stays at 1.5v. When I start even if the Maff is not doing the Job original does, should the volts not change on oxygen sensor?

If the ECU was faulty a lot of other problems would be visible? I can not imagine that just this one fault keeps coming up. Could I have a leak or fault on my injectors?

Aug 1, 2014 | 05:11 AM

cm60k

MBWorld Fanatic!

Joined: Aug 2006

Posts: 7,053

Likes: 398

From: A.D., U.A.E

2000 (W202 C200) & 2000 (W202 C55)

I don't think M271KE got MAF, it has "2" intake pressure sensors, isn't..?!?

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Aug 4, 2014 | 08:29 AM

Henry Bosch

Thread Starter

Newbie

Joined: Jul 2014

Posts: 7

Likes: 0

From: Johannesburg

2005 C230K Coupe

Quote:

Originally Posted by C230 Sport Coup

Any leaks in the brake booster? I just replaced mine for this, and finally after doing what you did, passed CA smog.

It was hissing you could hear it....

Hi, I will have a look when I get home. Would the brake booster make me use more fuel? This fault finding takes a lot of time. I don't mind but its cold over here so hands suffer.