'99 V70 2.4 NA - O2 sensors battle

fszczesniak · Post by **fszczesniak** » 18 Mar 2020, 13:12

Long story short, the fuel efficiency got really high lately - 14L/100km, so i started to dig into it. Just renewed my PCV, btw.

after a short diagnose with OBD Fusion, I noticed that my O2 sensors are not working correctly - S1B1 was stuck on about 0,5V and not reacting properly while driving. STFT's and LTFT's were also to high.

Got a new OEM sensor, installed it yesterday, engine is running smoother and nicer now, but the S1 is still stuck at about 0,5V! S2 post-cat on hot idle runs at about 0,85V....

I started measuring the voltages on the plug with my multimeter and got only 3,8V between battery negative and S! signal+ with the ignition on... what the heck is going on here?

Post by **misha** » 18 Mar 2020, 13:18

14l-15l/100km with automatic transmission in city traffic sounds normal to me.
If it is manual...then around 13l/100km.

I guess that it is a 20v car.

Did you removed negative battery cable for 10-15min after o2 sensor replacement...in order to reset ECU and fuel trims?

fszczesniak · Post by **fszczesniak** » 18 Mar 2020, 13:50

Heh, it used to be around 11/100

now even a very calm highway trip is not going under 10...
Yes, I did the reset procedure. Actually, during the lambda sensor replacement, the battery was disconnected the whole time.

P.s. yes, it's a 20v engine, non turbo, with ETM

Post by **misha** » 18 Mar 2020, 14:48

At highway speeds 120-140km/h it should be from 8.5l to 10l/100km.

*With automatic transmission

You mentioned that you replaced pcv system....could be that you forgot to connect some of vacuum hoses....creating a vacuum leak.
Or worst....intake manifold gasket not seated properly.

Did high consumption appeared right after pcv job?

fszczesniak · Post by **fszczesniak** » 18 Mar 2020, 15:16

I checked everything several times - was not my first pcv job

definitely vacuum hoses coming out from the intake manifold are in need of replacing, obd2 shows about 32kpa manifold pressure (don't know the specs). Planning also to smoke test the air intake, vacuums and exhaust in the nearest future

Post by **misha** » 18 Mar 2020, 16:41

What scan tool do you use for the car?
If it's some kind of android app and not VIDA,it can't be trusted.
In what shape is flexi pipe between exhaust manifold and cat?
If it's leaking,o2 sensors will report fault.
Also ...any exhaust leak in between exhaust manifold up to rear o2 will report fault and o2 sensors will not doing their job.

From '99 these cars use Denso management.
Is replacement o2 also Denso?
Bosch will not work on '99 and after.

fszczesniak · Post by **fszczesniak** » 18 Mar 2020, 23:27

Unfortunately it's not Vida, don't have access to that. I use obd fusion with elm Bluetooth adapter. Exhaust is to be smoke tested, because visually everything looks fine. Yes, it's a Denso sensor, OEM.

fszczesniak · Post by **fszczesniak** » 19 Mar 2020, 09:04

What is the actual way to test if lambda is getting enough voltage? I was thinking that you purely turn the ignition on, probe the signal plus (blue) when lambda connected, check voltage on the multimeter between signal + and battery negative... shows only 3,8V! tried also the same procedure on S2 sensor and there was nothing

Post by **abscate** » 19 Mar 2020, 09:32

Its a heated OXS so there are two circuits to check - both the heater circuit and the sensor circuit.

fszczesniak · Post by **fszczesniak** » 19 Mar 2020, 09:56

Yep, 4 wires (black black - heating, white ground, blue signal +). Checked heating circuit, 2 ohms, perfectly healthy (it's new after all). How do I check the signal circuit? What to probe and how?