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996 Carerra Coupe 2003 O2 and Mass Airflow sensors


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Hello Porsche experts, I recently purchased a used 911 Carerra, 2003 and had the fuel pump fail.  So I looked around in Orange County to find a Porsche mechanic and ended up taking it to Hergesheimer.  They replaced the fuel pump but a few days latter I experienced something very troubling.  The car would start but idle was somewhat rough.  Revving the engine was a challenge in the lower RPM 1000-3000 then it became a bit smoother when driving with load on the engine in the 3000-4000 RPM range.  Alarmed by this I called the shop to bring the car in, but this was the day before the Rennsport Reunion in Laguna Seca so I dropped by another mechanic who brought up these error codes on a generic diagnostics tool:
 
P0134 Sensor Circuit No Activity Detected (Bank I Sensor 1)
P0101 Mass Airflow Sensor / Circuit range issue Performance problem
P0154 O2 Sensor no activity detected (Bank 2 post CAT )
P2098 Post Catalyst Fuel Trim System Too Lean Bank 2
P2096 O2 Sensor no activity detected Post Catalyst Fuel Trim System Too Lean (Bank 1)
P0156 O2 sensor circuit malfunction (Bank 2 Sensor 2 post CAT)
 
 
Initially I thought this was related to the fuel pump replacement. So I called the shop who did the work and they said bring it over.  Their analysis identified similar codes and they suggested a few hours to review the harness and sensors in order to asses the problem.  A week later i am still trying to resolve this and wondered if I should replace the O2 sensors myself.
 
I have done brakes and other minor maintenance.  What is the opinion of the forum here on next steps?  I can provide further detail 
 

 

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0134 - Bank 1 precat sensor (no activity detected)

o154 - Bank 2 precat sensor  (no activity detected)

0156 - Bank 2 postcat sensor  (no activity detected)

 

2098 Bank 2 O2 sensor aging (too slow)

2096 Bank 1 O2 sensor aging (too slow)

 

0101 - can't find this for an '03. Are you sure this number is correct?

 

Do you have a generic scanner that can read real-time sensor values? If not, it's better to leave this to a shop to diagnose. I doubt it's any of the O2 sensors as it's unlikely they all go bad at the same time. It's good to check the harnesses/connectors but it;s also unlikely they all go bad at the same time.

 

I suspect you have a gross vacuum leak/bad ignition coil that's causing misfires. All the unburnt oxygen is read by the O2 sensors.

 

One fast way is to use a scanner to try to read the voltage of all the 4 O2 sensors.

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Hello Ahsai, thanks for the response...

  • I started the car again and listened to the engine in the trunk - no major hiss- when I removed the oil cap the engine dropped significantly and almost cut out.  replaced the cap and back to a rough idle (varying between 650 RPM to 1100 RPM)
  • I lifted the oil filter tube but did not observe any cracks or leaks however these may be located further back beyond view.
  • not sure how to test for vacuum leak / bad ignition coil ...
  • I will voltage meter test the O2 sensors.  Where should I do this?>>  Engine compartment or behind wheels?
  • Diagnostic scanner - which do you recommend for purchase? (http://www.durametric.com/buyus.aspx; or alternative?)
  • I decided to go for a drive as the car sat for a few days.  It started well and drove well for a few blocks then the issue creturned.  I shot a small video (2MB) if that will help in assessment.
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  • Moderators

 

Hello Ahsai, thanks for the response...

  • I started the car again and listened to the engine in the trunk - no major hiss- when I removed the oil cap the engine dropped significantly and almost cut out.  replaced the cap and back to a rough idle (varying between 650 RPM to 1100 RPM)
  • I lifted the oil filter tube but did not observe any cracks or leaks however these may be located further back beyond view.
  • not sure how to test for vacuum leak / bad ignition coil ...
  • I will voltage meter test the O2 sensors.  Where should I do this?>>  Engine compartment or behind wheels?
  • Diagnostic scanner - which do you recommend for purchase? (http://www.durametric.com/buyus.aspx; or alternative?)
  • I decided to go for a drive as the car sat for a few days.  It started well and drove well for a few blocks then the issue creturned.  I shot a small video (2MB) if that will help in assessment.

 

 

The Durametric software is a good as you are going to get without spending a ton of money.  You can purchase it directly from them on their website: http://www.durametric.com/default.aspx

 

With the system, you can read the sensor voltages in real time while the engine is running.

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Like John said, Durametric will be ideal for DIYers.

 

For O2 sensor related diagnostic, I also love the bluetooth OBDII dongle + Android Torque app.

 

No, you don't need to do the low level voltmeter checks yet (unless you really wanted to) if you have a scanner that can read the O2 sensor voltage via the DME. In fact, you want to know what the DME reads without disturbing the wires yet. The signal voltage on ALL O2 sensors should read ~0.44v whenever you turn the key to the last position before cranking. If you don't even get this voltage, something is very wrong with the wires/sensors.

 

Then when idling on a fully warmed up engine, the pre-cat sensor voltage should swing between 0.2~0.7v and the post-cat sensor should be pretty steady at 0.7v. When driving, if you accelerate abruptly, both the precat and postcat will show high voltage (> 0.7) and if you decelerate suddenly, both will show about 0v.

 

http://rennlist.com/forums/996-forum/810606-obd-ii-code-reader-recommendation-2.html#post11299728

 

Also, you can check MAF reading at idle. Should be ~4g/s.

 

If you use Durametric, it can show cyl misfires in real-time.

 

post-5282-0-66914100-1443649641_thumb.jp

Edited by Ahsai
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BTW, to trace external air leak, you use a smoke machine or carb cleaner method (more dangerous). Re bad ignition coil, misfire count will show in Durametric and pending or active misfire codes will be returned by a generic scanner.

 

I don't see any video in your post.

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  • 2 weeks later...

Ahsai / JFP, thank you for your feedback. I went into the shop and they replaced the O2 sensors with test sensors.  Car idle and performance was immediately stabilized.  Bought and installed 2 new sensors $260 ea. with labor came to $1K.  I wish I had done this myself... but I wasn't sure about the assessment so I didn't want to buy sensors and be wrong and start stocking Porsche parts

 

ROOST

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