How do these OBDII values look?

[mclasser]

I was messing around with the Torque Pro app and the Bluetooth OBDII adapter I got for Christmas. This is my first time looking at different performance values, so I don't know much about deciphering them. I was wondering what you guys thought about these values in my 02 Accord 4-cyl w/212k miles. It's not extensive but should hopefully give an idea of how the old girl is doing.

Car was idling in park, no accessories on. I had come back from a 10 mile highway trip to warm things up. Ambient temp was 35F & raining (if that makes any difference):

RPM: ~700
Coolant temp: 198F
Throttle: 10%
Vacuum: 20.2 in/Hg
STFT: fluctuated b/w 1-3.8%
LTFT: 0-0.8%
B1S1 O2/ A/F sensor: 0.8V
B1S2 O2 (the one that monitors the cat I presume): 0.05V

Revving up to 2500 RPM did not drop the fuel trim values, which I read online means I don't have a vacuum leak. But...voltage seems low for the B1S2 sensor. Ive changed the upstream sensor but the downstream is factory. Looks like it's starting to get lazy...?

 

[Thax]

Looks pretty good to me. Fuel trims are good , vacuum is good. Downstream sensors do not "switch" like upstream sensors, they need to carry a fairly consistent voltage. If it was switching voltage like the upstream sensor , it would be a good indicator your catalytic converter is on its way out.

 

[irad]

Throttle should be 0 at idle, clean throttle position sensor and throttle plate. B1S2 O2 sensor should be .4 to .6 at idle. .05 is too low, minimum is .1v.

 

[supton]

Sounds like the downstream sensor is dead. I had the same thing happen on my '99 Camry. You'd think it'd toss a code, but it didn't. I slapped a (Denso? whatever was recommended) and absolutely no change to the car afterwards--no change in idle, mpg, etc. The ECU just simply didn't care. Maybe I should have tried unplugging it, see if it would toss a code.

 

[clinebarger]

Originally Posted by irad
Throttle should be 0 at idle, clean throttle position sensor and throttle plate. B1S2 O2 sensor should be .4 to .6 at idle. .05 is too low, minimum is .1v.


Don't believe every PID when using cheap scan tools, Data stream update rate on a 2002 Honda isn't the fastest either.

 

[Skippy722]

Originally Posted by supton
Sounds like the downstream sensor is dead. I had the same thing happen on my '99 Camry. You'd think it'd toss a code, but it didn't. I slapped a (Denso? whatever was recommended) and absolutely no change to the car afterwards--no change in idle, mpg, etc. The ECU just simply didn't care. Maybe I should have tried unplugging it, see if it would toss a code.

Honestly, if it isn't throwing a code I will never change my downstream o2 sensors. That being said, I replaced only the upstream o2 sensor on my Caliber because it was only getting 20mpg no matter how I drove it. No codes were thrown. After replacing it with a new NTK, I was averaging 25.

 

[14Accent]

All those numbers look fine. STFT is perfectly acceptable +/- 10%, same with LTFT except I prefer +/- 5%.

O2 readings aren't really relevant with an engine at idle. You need to graph them while driving. A healthy upstream will swing from ~.150v to ~.850v at a steady, flat cruise. A good downstream O2, while monitoring a healthy cat, will swing between ~.350v to ~.650v and stay relatively flat. Hovering around .450v is just about perfect.

In the most basic sense, an upstream graph should look like: /\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\

A downstream graph should look like: ----_____----____-----____----

Where the upstream switches between much higher peaks and valleys, in much quicker succession, whereas the downstream varies little and holds flat for longer at a time. Keep in mind, that's not to scale.

 

[ka9mnx]

Throttle body needs to be cleaned or TPS needs replacement (can be checked with an ohm meter). O2's are long overdue. Maintenance item that should be replaced every 100k miles.

 

[mclasser]

Thanks for the replies, guys. I watched the values while driving today and the downstream O2 would get up to 0.7V. When idling, it would again go back to 0.05-1V.

 

[cjolson140]

I think the throttle is just fine - every car I've ever scanned reports a similar non-zero TPS value at idle. Many never reach 100% either, even with the throttle held open at the manifold. Just the way some TPS sensors are.