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Discussion Starter · #1 · (Edited)
After having done every fix to finally cure my lean codes, it really threw me for a loop when I went to the CA smog station and failed my test for no apparent reason. As of Feb 2016 our BMW's can only go to Star designated ones which meet higher performance standards established by the Bureau of Automotive Repair. After talking to the owner of the station, the take away I got was that CA is going to be stricter and I was right.

While I had no codes and my car was running great, I failed the smog test for only secondary air injectors not ready. This was new to me, and I was pissed, but with smart phone in hand, I did a deep dive into what the heck this was all about, and developed a plan for those who want to save time trolling the internet for a solution.

Action Plan:

1. Read every post on the subject written by the infamous JFOJ. He is a ninja on the subject and without him I would have probably ended up at the dealer with a bill of $500-1000, not kidding.

2. Buy yourself a wifi/Bluetooth OBD2 reader - I bought the Veepak on on Amazon for $17 (this is compatible with iphones)

3. Buy OBD fusion for iphone or android - this software is intimidating because if very comprehensive. Don't be scared, JFOJ has provided PDF instructions for setup and use.

4. Learn to graph and analyze and graph the log files created by OBD Fusion so you can tell which of the 4 Oxygen sensors are lazy. The voltage for O2 sensors oscillates, meaning voltage readings of their performance goes up and down over time.

After graphing results (probably 10 times from 5 minutes runs in my car) I concluded my pre-cat sensors, while not completely dead, were not oscillating to the desired range. I changed them and then used to the software to determine that my secondary air injection system was now ready. The pre cat sensors took me 30 minutes to change.

What a PITA, but after 5 hours of studying, 2x O2 sensors @ $70, 1 wifi reader $17, and the iphone software $10 - I consider my lucky. Note that if the pre-cats didn't solve the problem, next I would have changed the post cat ones. If that didn't solve the problem then your next recourse is to go to a referee smog station. At this point you could have enough bills (they want to see about $650) so good chance, if there are not other codes or readiness monitors issues, they will pass you.

Hope this helps you, BTW I drive a 2002 325i with 160k.

Premium Member
28,968 Posts
Good summary that will hopefully help others.

But the bottom line is this, 2 important things to pay attention to.

Before you get a car or your drivers license you really should get OBDFusion and an interface. You cannot maintain a car newer than 1995 without an OBDII tool. You do not need something expensive, and you do not want to buy sometime more specific for your first too. $30 is less than and oil change and an OBDII App like OBDFusion is a MUST, especially if you live somewhere SMOG or Emission Tests are required. An OBDII App is MUST if you live in the great county of California because most auto parts stores in California DO NOT loan OBDII tools.

Pre-cat O2 sensors are important for Readiness Monitors. They are the key to almost all of the readiness monitors. O2 sensors NEVER trigger a code unless the heater circuit fails. I have been working on cars a LONG time and I can probably count on one hand the number of times a bad O2 sensor has triggered a code that meant the O2 sensor and not the heater circuit is bad. If your car is over 10 years old and 100k miles, REPLACE the pre-Cat O2 sensors as they are CONSUMABLE. They do not last forever. Why wait until you are up against a time crunch with an SMOG/Emission Inspection before you change the pre-Cat O2 sensors?? They all get lazy as they age and degrade and they will cause problems first with SAP errors or Readiness before they will ever degrade enough to trigger any codes.

Like many things, you can choose to replace the pre-Cat O2 sensors on YOUR schedule and shop for best pricing or you can wait and be painted into a corner and replace the pre-Cat O2 sensors when you are up against a time constraint and may actually fail a SMOG or Emissions Test. If you are wise and purchase an OBDII App like OBDFusion, you will KNOW long before you get in line for a SMOG or Emission Inspection if you have Readiness Monitor, Pending Codes or even an OBDII port that does not have power due to a blown or missing fuse.

EVERY E46 on the road needs a replacement fuel pump and pre-Cat O2 sensors IMHO.
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