Loni313

I have 115k miles on my e60, I suspect a bad o2 sensor because i've been losing MPG lately but i have no CEL
The o2's all should be original since i purchased the car @ 30k Miles so i know thats beyond the life span of a typical 02
Im just not sure if i should rely on waiting for a CEL to replace them or just go ahead and swap them.
I'd figure if the Secondary/After Cat's 02's were bad they would more likely throw an increased emissions code then if the primarys were bad so im leaning towards
switching out the primary 02's for now since a whole set of 02's look to be around $600 for OE sensors.or should i just replace all?

I was just wondering if anyone had a bad 02 w/ no CEL??

pauliehcfr

They won't always throw a CEL. Sometimes you can get a lazy O2 sensor where it doesn't respond quickly thereby sending updated emissions data to the DME (engine computer) Try reading the codes first, sometimes a code will be stored but not turn on the CEL because it has to see the fault for x amount of drive cycles. If no code is stored, and you suspect an O2 sensor, you need to look at the O2 sensor values on a good scanner. The sensors in front of the catalytic converter should be constantly changing and the sensors behind the cat converter should remain somewhat at a constant value. Other things that can cause poor mileage are dirty air filter, clogged fuel filter, worn spark plugs, vacuum leaks, dirty intake, brakes that don't fully release, low tire pressure, faulty mass air flow sensor.... start with reading the codes first though.... BMW recommendations were to replace o2 sensors at 100k miles

Loni313

Thanks for the info,
I think i found my problem. I used the hidden menu to accesss the coolant temp sensor.
I kept it up on display while driving and idling, during a 30 mile drive the temp stayed as low as 63c and never passed 66 degrees celsius(150f)
at idle, it was really strange, it went from 72,73,74,75,76,77 and then back down 76,75,74,73,72 then back up and down in the exact same way consistently.
It was almost like clock work with a change in temp every 2-3 seconds to the next degree.
numbers are far off from the usual operating temp of a fully warmed up motor.
I ordered a new temp sensor and thermostat from RMeuropean.com

Are there any good scanners for our cars that log real time value's for MAF Grams/Min, O2 Voltage, EGT, LTFT's and so on?
With Audi i used Vag-Com which was a really great tool to have. catching dying Maf's and O2's was easy to spot.
I was looking at the Kiwi PLX for the Iphone/Ipod touch. Doesn't look too bad

Since you let me know that o2's do go bad in these cars w/o a CEL, I'll probably go ahead and swap them out since even if they still are working it probably wont
be long untill they die since they have 115K on them