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Thread: Fault Code
08-06-2010 10:53 AM #1
08-06-2010 12:05 PM #2
- , PacNW, This oneMember No: 170217
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08-06-2010 06:39 PM #3
It isn't the cats - primary oxygen sensors
"Catalytic Converter Efficiency Below Threshold, Cyl 1-3 (or 4-6)" is a common code you may get if your primary oxygen sensors are bad.
A mistake that even many so-called professional mechanics make is assuming that since an OBD II code MENTIONS a part by name, that the cure is to replace that part.
No. NO NO NO NO NO!
It is a diagnostic code telling you a condition. You have to think about what can cause that condition, not merely "read code, replace named part" like the warranty monkeys at the dealer.
On two of my 2.8 BMWs, I got this code. In both cases, replacing the primary oxygen sensors was the cure. Code went away and stayed away.
Primary oxygen sensors should be replaced at about 10 years and 100,000 miles. Mine were 13 years old and at about 80K miles. They just go bad over time.
When the O2 sensor goes bad, the engine runs rich, and the catalytic converter operates below efficiency. QED.
In a similar vein, a code reading "Oxygen sensor out of range" or "range limit exceeded" does NOT MEAN you should replace the oxygen sensor!
Instead, look for cracks in the intake elbow, causing unmetered air to enter the system. This causes the computer to index the sensors to compensate, until the range limit is reached, generating the error code.
The intake elbow is a $15 to $30 part and takes minutes to replace. This has happened on two of my BMWs (2.8 and a 3.0).
Again, just because an OBD II code mentions a part, the cure is NOT to replace that part, in many cases. IN some cases, yet (O2 sensor heater wire, for example, but check the connectors, first!).
BTW, never be in a hurry to replace cats. They are expensive and usually last the life of the car. Aftermarket ones are usually crapola and don't work with OBD II systems and thus cause more problems than they solve. I'd rather install used ones from a junked car than buy aftermarket. Cheaper, too.
I've read a number of threads here and elsewhere of people who replace cats (with aftermarket crapola) in response to this code, only to create a SECOND problem. Then, they replace the oxygen sensors and the problem still exists because the aftermarket cats aren't working properly. So they get frustrated.
Secondary oxygen sensors can also be a culprit, as they measure the O2 levels after the cats and monitor the efficiency of the catalytic converters.
But I suspect it is the primaries, unless you have replaced them recently.
BTW, use OEM-style plug and play Oxygen sensors. It ain't worth saving $50 to solder on "generic" sensors from eBay.
Sensors for my 3.0 were about $65 apiece. For the 2.8, they were about $108 from Pelican parts.
08-06-2010 06:41 PM #4
08-13-2010 10:42 AM #5
Re: Fault Code
thank you gentlemen. Your comments were very helpful. I had suspected that it was the pre cat sensor. I replaced it once around 70K mile. I never replaced the post cat O2 sensor as of yet. I think Ill just buy a pair and replace both and cross my fingers that it sovels the problem. Ill post an update.
Btw the acutal fault code on the the peak tool is:
Table 07 28: Catalyst efficiency.
1997 BMW Z3 1.9 165K
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