we had the infamous check engine light on a 2001 Volvo V40. P0133 or something, the one about O2 sensors. We replaced the O2 sensors this morning, and the mechanic said that we have to drive it about 50 miles before the internal computer will reset, even though the check engine light is gone. Never heard of this... but ok... he won''t re-test our car for emission check, so what can I do. Drove 50 miles.

We came back to the shop, he plugged in his OBD II scanner, but he told us that it was still not "READY" to be re-tested yet!? After a full day and 50+ miles of driving after the O2 sensors repairs!? What is he talking about? He said he can''t test the car until the internal computer is reset. The OBD II scanner that I owned shows NOTHING. He said he doesn''t know when it will be ready, just come back every day and he''ll try.

??

have you paid this guy yet?

Yes, only for the emission test. It failed, with the P0133 code. So the dealer (weird situation, the small independent dealer is next door and friends with this mechanic shop) simply paid this mechanic who replaced the O2 sensor. We did not have to pay for it, only paid for the initial emission test of $30 or something.

The SAME mechanic (who replaced the O2 sensor) is now telling us the car is still not ready to be re-tested. He can't tell me to replace the O2 sensors again because he was the one who replaced them! The check engine light came on, and I plugged in my own OBD scanner, saying P0133 again. Is this what he is talking about? The code will keep coming back until whatever this internal computer is reset and recognizes the new O2 sensors?

Thanks.

did you erase the code? i know, stupid question, but sometimes when we are frustrated, people tend not to see the obvious. anyway, drive it around like that for a week, or even better, find another mechanic. i mena you paid the guy. also, since you are in the US, try cartalk.com and plug in your zip. there is a forum for finding a mechanic. good luck and keep us posted.

yeah i used my OBD scanner to reset the light, but apparently according to others on the forum and the mechanic, there is an internal computer that needs to be reset, not doable via the OBD scanner. It either takes time or mileage for the car to learn that the new sensors are replaced.

hey bro, road trip. let everybody else celebrate father's day without you. hit the road and redline it. just by sheer amounts of speed, the false code will be left 1/2 a state away while you make your getaway. :grin:

disconnect the car battery for a minute or find the efi fuse under the bonnet in the fuse boxand pull that for a minute, this will erase your codes and reset the adaptions. If the fault reoccurs after that its because it is not fixed.

ok I will try to battery and fuse thing. How could it not be fixed though, we saw the guy pulling out the old O2 sensor and putting in the new one. As instructed by the P0133 code (bank 1).

UPDATE: Tried all the battery, fuse disconnections. Tired putting on 100+ miles, and 4 days of driving. Nothing can reset the Check Engine Light.. if anything, the idle speed is now under 1000 RPM, a bit odd. I used my OBD scanner to reset the light, and of course, 3-cycles later the internal computer still detects whatever P0133 O2 sensor problem, and the light came back on.

Dealer and mechanic finally conceded that maybe the O2 (Bosch, brand new - we saw them opening the box and installing it) is defective. Ordered new one, and will re-install tomorrow.

I just want the damn car to pass emission!

OK. OK . ok... I just registered an account here to answer your question...

What your waiting for is ECU Monitors that show a "ready" when the system has completed its "readiness" test Now... in the state of texas you can have 2 "not ready" in in the ecm and still run the test...

Check with your mechanic or a auto zone to see for a readiness test..


im working on a 01 V40 with the same code.. im trying to figure out whats wrong..


i replaced the 1st precat. sensor and i am still recieveing the error code.. so >_>

keep in touch

-Tyler N Austin.TX

I dealt with the same thing on my '01. I looked around all over the web, talked to mechanics at dealerships and independents, but noone was sure what to do. So I figured it out the hard way.

Even though the computer is telling you the front (before cat) O2 sensor is the problem, it's actually the after cat one. Replace it and you should be fine.