'98 V70 NA 5spd manual -- P0133 & P0140

[E Showell]

Highway driving yesterday and the CEL came on. I did not notice any change in performance, no rough running, no new exhaust sounds. The front O2 sensor at least is a relatively new Bosch unit. About 2 years ago I did a complete exhaust system replacement including CAT. PCV was done a while back and I did not notice any vacuum leaks at the time. I'm suspecting a vacuum leak of some kind. Also, I do not have the updated intermediate O2 sensor harness and I have had a lot of oil on the cam cover of late, but it has all been cleaned up and the source of the oil leak eliminated. Any thoughts?

Time to get a length of aquarium hose and a cigar? or to start spraying carb cleaner around?

[dosbricks]

Your logic appears sound. One would think that this extreme cold weather would cause any brittle hose to be more susceptible to cracking from normal engine torque/vibration.

[E Showell]

I actually did a search and found one of my own old posts from 2013 (I think around May) relating to the exact same twin codes. At that point, I simply turned off the CEL and it didn't reappear until now. I'm going to update that post to better document the time interval between reappearance of the codes, but since the car appears to be running well, I may take the ostrich mechanic approach again.

[dosbricks]

Yeah, I know what you mean. I just got PO133 on my wagon this past week and changed out the front O2 sensor. But for several years I've gotten PO422 two or three times a year. Probably because I have an aftermarket HP cat in there and romping on it (rare, but known to happen) overwhelms the ECU parameters. I just clear it, drive on, and enjoy the nice throaty growl it imparts.

[esl_97_850_T5]

I'm like you. I'd opt for the ostrich approach, unless it starts happening more frequently.

That being the case, here's my understanding of the codes...

P0133 can be manifested due to front or rear O2 sensors. There are 2 separate source errors that can be seen on a Motronic 4.4 or Motronic 4.3. That's the reason owners occasionally report seeing double P0133 errors. One of them is for the front O2 sensor, the other is for the rear O2 sensor.

P0140 relates to the rear O2 sensor.

Faulty component / OBDII code / 3-digit code / raw DTC in hex reported by ECU 7A (Motronic 4.4):

Front HO2S / P0133 / 4-3-5 or EFI-435 / 0F
Rear HO2S / P0133 / 4-3-6 or EFI-436 / 10
Rear HO2S / P0140 / 4-2-5 or EFI-425 / 11

I think the detailed meaning of the codes is actually "EFI-435 Front HO2S slow response" and "EFI-436 Rear HO2S compensation" and "EFI-425 Rear HO2S lambda sond control" (or "EFI-425 Rear HO2S ideal air-to-fuel mix control").

Assuming that's true, the "tests with codes turbo.pdf" of Volvo_850.zip or its online HTML version on Volvotips suggests that the testing for 4-2-5 (ie, P0140) code should be performed first, then the testing for 4-3-6 (if it's the reason for the P0133), then the testing for 4-3-5 (if it's the reason for the P0133).

You could also display this volvopedia.de link with Google Chrome, let Google Chrome translate it, then click on the EFI-425, EFI-436, and EFI-435 links in succession letting each of them also be translated.

Since you've replaced your front O2 sensor, I'd guess that your rear O2 sensor is occasionally producing the P0133 and P0140.

But if you want to hone in on what the codes really mean, you should be able to read and interpret them with Vol-FCR Full or Brick-Diag Free. Even the volvo850diag / kwpd3b0_interpreter duo can differentiate them now.

Since I don't have a Motronic 4.4 or a '98 S70/V70, it could be some of this "mashed together from multiple sources" info is faulty. Please correct if you're certain it's wrong.

esl_97_850_T5

[E Showell]

Thanks for the thorough response. I've inadvertently got two distinct threads going on this since I posted about those codes in May of 2013.

I found the lower air box vacuum hose completely out of its corresponding elbow and am betting that's what caused the codes to set. I've been updating the other thread.