Mity2

Sooooo I got code yesterday.
Which is H6which is Right bank O2 sensor Lean exhaust indicated.

So I first cleared the code, and drove around.
And it came back on again��
Here are few things I’ve noticed.

When your cruising around, it doesn’t come on.
It comes on when it sits there and idle for about 5 min.

And when it does, fan kick on even my AC isn’t turned on
And I also hear what can only described as “motor whining” noice right before it comes on.

Seems to be getting real gas mileage(per dash instant mileage. About 15~20mpg@ 55mph with cruise on
(Perhaps what’s what it was always getting? I never paid any attention until not to be honest)

Slight shake(may be?) at while driving(May be as if I’m getting a missfire?)


Soo where do you guys suggest I start.

Edit: its 1995 base A/T with 55k

Kevova

Vacuum leaks. Noise what does driver information center read for temp it's the temperature PCM is reading. Gauge uses different sensor. Is cooling fan or AIR pump coming on?

Mity2

Fan did come on.
i did not read the temp read out. It couldn’t have been hot enough for the cooling fan to come on tho
I don’t know about the air pump.

Kevova

Low coolant more so, but also a stuck thermostat can cause erratic gauge operation. ECM turns on fan.

Mity2

So I had it hooked up to OBD1 scanner at friend's garage.
It flashed SES light in dash on the way there. But then it went out before it got there, which is new.
Anyway, it pulled:
DTC 64 – Bank 2 (Right Front) Heated Oxygen Sensor (HO2S) #1 Circuit (Lean Exhaust Indicated)
which is what I have been having. But this time, it also pulled:
DTC 63 – Bank 2 (Right Front) Heated Oxygen Sensor (HO2S) #1 Circuit (Open Circuit).

Then I ran the real time data acquisition mode, and it read 4mV with key on/ but engine off. then once engine turned on, it went all over - as high as 850mV, and down to 100 something mV. never seem to settle anywhere, which I'm told that's normal
according to my GM service book, it says:

"Sensor is like an open circuit and produce no voltage when it is below 315°C(600°F). An open sensor circuit or cold sensor causes "open loop" operation. Whenever ignition is on, voltage is supplied to the HO2S heater on CKT241. Even with engine not running, HO2S will reach the operating temp, and indicate O2 content of the exhaust gases at the sensor" Page 6E3-A-120

Engine temp on dashboard read out seem normal - coolant temp a around 190°F

I just drove there, so O2 sensor should have been up to operating temp, and in same page, it says the range of HO2S signal voltage should be at typically at around 450mV at the key-up., and as high as 1000mV if exhaust is rich, down through about 10mV if exhaust is lean.

So 4mV seem too low no matter how I look at it.

DTC63 says open circuit. I thought it came on because HO2S read 4mV, which it says it'll act like open circuit in above.
But when I look at the actual description of DYTC63, it says:
"DTC63 will set when engine is at normal operating temp(above 70°C/158°F which it was), engine operating more then 2min, oxygen signal voltage steady between 350mV to 550mV, throttle position angle above 5% and DTC21 and 22 not set(which they aren't). all condition met for about 60seconds"
which seem contradicting to DTC64 turn on parameter, which says "Fuel trim enabled, and signal voltage remains below 200mV for 50sec"

what do you guys think

Kevova

The HO2 heater failure I would check sensor has power and ground for heater. If it does, replace HO2 and re-evaluate.

Mity2

thats good point. Will check that tomorrow.
But if heater failed, would it still read the any value at all?

also, when it says it’s running on open loop, what does that mean?

Kevova

Open loop is preprogrammed operation without feedback from O2. Once O2 heats up and becomes active the PCM adjusts engine operation based on o2 voltage. The heater shortens the time ii takes to go into closed loop.

Mity2

Would being in open loop causes a miss(or hesitation, more like) under load?

Kevova

Maybe, being lean will cause those symptoms.

Mity2

I went back to my friend's to hook my car on to his Snapon Verus scan tool(I want one of them for myself!!!) again to do little more digging.
I think its my right upstream O2 sensor acting up is what causing all these issues..

Today, It pulled DTC63 only. No DTC64...





I know somehow feedback from right sensor is on left, and feed back from left sensor is on right(I don't know how to fix that).
but you can clearly tell that right front O2 sensor is giving PCM some funky feed back compared to left O2 sensor.

So im thinking replace right upstream with new one to start..?

I did check Fuel pressure just to rule out the lean caused by lack of fuel, and seems to be doing just fine(42psi at key on, droped to about 37~39psi with car on idle, shot up to 46psi with vacuum line disconnected at pressure regulator while idling, maintained 37~39psiat constant 2000rpm, but shot up to 46psi when revved quickly)

ctmccloskey

I have seen this happen before on another C4 and it is from the O2 sensor "cooling off" and ceasing to work after idling for a short period. When the car is driven a bit further getting the O2 sensors get back within normal operating temperatures all goes back to normal.

It can be fixed by switching to a "heated" style O2 sensor, heating it using electricity keeps the output more stable which helps the ECM make faster changes. IF you already have heated O2's then your O2 heater is not working properly. New Part time and I have been very lucky with RockAuto on O2 prices.

I still live by replace the O2 sensors every 50,000 miles. O2 Sensors have a bad habit of slowing down (lagging) as they get older. Slower O2 readings mean less performance and economy.

Good Luck and I am real anxious to hear what happens!

Gotta Get That Corvette on the Road!

Kevova

63 is open circuit right pre cat O2. Open circuit could be sensor reading isn't getting to.PCM. You need a trouble chart. Purple wire will have .45v key on, it is the signal wire. The tan wire I don't have a value other than 0. It could be ground. The 63 trouble chart will have more details.

Mity2

I thought of that, but if sensor reading isn't getting to PCM, I wouldn't even get the reading on the scanner tool as date for scanner comes from PCM?

ctmccloskey it already has 4 wire O2 sensor, so it is heated(or supposed to be anyway)

Kevova

I don't have your FSM. So not clear how tan wire functions in circuit. In the.past the 02 grounded through sensor body at manifold. 4 wire diagram indicates tan wire would be ground. Anyway the PCM sends a .45 volts to the O2. When the O2 gets hot and becomes active it should generate a voltage over .45v. When that happens closed loop operation starts and PCM uses O2's generated voltage. If circuit is open PCM just sends 45v ; scanner will only show a fixed voltage. PCM may expect to see the .45v on tan wire during the warm up timer. If doesn't PCM sets code.

Mity2

Correct. It should read .45v(or 450mV as my FSM states) upon key on until it warm up.
I saw 4mV. Key on.
then it sort of stuck at around 350mV after it started(see my first picture I posted). But then they did the odd fibrillation thing(on second pic). All while left side is doing what it supposed to be doing

Kevova

Was that with scanner or voltmeter?

Mity2

With scanner

Kevova

Go the the connector and measure voltage key on from purple to ground and purple to tan see what your readings are.

ctmccloskey

Replace the particular O2 Sensor (right hand Upstream) and I will bet your Corvette's sensor issue will go away for good!

The Heater circuit in the O2 sensor is broken or not working properly on that particular O2 sensor. Replace it with a known good unit and you will see the problem go away providing it's heater element is still good. Sometimes dirty connections can interrupt the signal but not always

Your O2 is "cooling down" and shutting down which is why you have the code. Having a heater that is worn out or broken is useless and will do exactly what is happening to the OP's car. I have heard of this happening and it has been the O2 sensor on each car that had the problem. Seriously even if it is a four wire element something is letting it cool off and cease to be useful to the ECM. You might have a bad connection, bad ground or bad sensor.

I have tried to tell you guys, I have seen this before and am pretty darn sure I know what I am suggesting is likely the cause of the problems.

The LT-1 is a different beast than my C4's anemic L98, but I have broken 30 mpg on the highway cruising at 60 with cruise control and AC on and stereo blasting. I also have the 700 R4 and 3.07 final ratio which might help a little bit. I have taken this car on many trips and have always seen above 25 mpg on the road.

Lets get this Corvette back on the road where it belongs!!
Best Regards,
Chris