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DMV can't read catalytic convertor on my 2003 BMW Z4


I find myself between a rock and a hard place with my emissions inspection. My car is a 2003 and has passed emissions inspection several times in the past. However last week it has failed twice due to the catalyst and oxygen sensor monitors not being ready (“Monitors not ready: catalyst, oxygen sensor”). My mechanic checked the catalytic convertor via his computer readouts and found it is working fine. The DMV policy says it will provide a waiver if a qualified mechanic completes at least $848 in relevant repairs but my mechanic says in all honesty there’s nothing to repair. Is my mechanic wrong? Any other suggestions?

Was the battery disconnected recently? If so sounds like the problem will be self healing given a certain amount of starts and miles.

Sounds like you are due for O2 Sensor replacement. They do not last this long…10 yrs is pushing it…13 is a wing and a prayer. Simple to change…and just good preventive maintenance actually.

This is the very first thing I would do. I would also look for any exhaust leaks…leaks can and will contaminate the reading of the downstream O2 sensor…making it think the cat is not doing its job…and posting cat efficiency codes.

I would be looking hard at the O2 sensors…and if they havent been replaced…replace them.


Good suggestions, thank you. I will see about replacing the O2 sensors. Any other thougts much appreciated.

“I would be looking hard at the O2 sensors…and if they havent been replaced…replace them.”


In addition, the OP should give serious consideration to replacing his mechanic, as a mechanic who doesn’t understand the correlation between bad O2 sensors and this alleged catalytic convertor problem is not much of a mechanic, IMHO.

For the reasons already articulated.
I should add that depending on what state the OP lives in, the inspector may be just a state inspector and not a mechanic at all.

OP, you may be confusing “monitor not ready” with “repairs needed”. Monitor not ready means the computer hasn’t detected enough drive cycles since the monitor was last reset. It has to have tested a variety of driving conditions to verify the converter is working correctly.

Normally the monitors don’t ever get reset in normal driving, so most car owners never have this problem. But the monitor can get reset by disconnecting the battery, or by using a scan tool to reset it. In any event, once a monitor is reset, the car computer’s software requires the car be driven enough to go through all its testing processes to verify the cat is good before the DMV can perform an emissions test.

You might wonder why all this rigamoral? It’s done that way to prevent owners from disconnecting the battery to clear the diagnostic memory in order to pass emissions testing. In effect, your car’s computer is tattling on you. Suggest to contact a BMW dealership who should be able to tell you exactly what driving events have to take place to ready the monitor for emissions testing. That will be a lot cheaper than replacing the cat. And even if you do replace the cat, you still have to go through the monitor readiness driving events again.