Car won't go into Closed-loop... LOSING MY MIND!!!!

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Hello All,

Been searching, researching... beating my head against this!!!

Basic info
2002 Z06
LG long tube headers, no cats (installed 3 years ago...)
Vararam (installed 3 years ago)
Replaced O2 sensors today ... (previously replaced o2s 4 months ago)

The problem started off as the passenger OS2 flat-lining voltage at 5ish mV all the time... closed or open loop. The car ran terrible obviously when in closed-loop, but runs fine in open-loop.

Since the o2s were only 4 months old I thought it was the LG flat-to-square o2 adapters (see pic1)... so I replaced them. After replacing them I kept blowing the o2 fuse (#15). SO I unplugged the the o2s from their wiring and the fuse stopped blowing. Now I thought one or both of the o2s had shorted. I bought new o2s again and installed them today. The fuse stopped blowing... BUT now my car won't go into closed-loop and the o2 voltages stay right on 450ish mV. I also have DTCp0134 and p0154 (02 circuit no activity detected) errors.

I have tried flashing back to the factory tune... and even doing a write all (scary...). Nothing works. Again the car runs fine in open-loop.

Any advice would be greatly appreciated, I am losing my mind over this.

pic1.png3-7-2022.hpl

[Matt Vardaman]

Why do you have to run adapters? Can you not run the oxygen sensors that are meant for the car? It's definitely a wiring problem. Because the log just shows the voltage of being disconnected and the car running in open loop. Hopefully one of the guys will comment that are super familiar with the sensor wiring on your application.

Have you traced the wiring for the O2's to make sure it's not rubbed through or make sure the wiring has continuity?

[[email protected]]

I am (and have been running) the rear type o2 sensors in the upstream sensor positions. The adapters change the plug type. It is just one of the ways to deal with having LT headers on a c5. It has been running great for years... Things are pretty tight in a c5 engine bay... I had planned on checking the ground points starting tomorrow. I hate electrical problems... ghost in the machine nightmare.

[blindsquirrel]

Unplug both O2s. Key-on, monitor B1/B2 O2 mV readings in scanner. Do they sit at the default 450mV, and no blown fuses?

If all that is normal with the sensors unplugged, you need to identify each circuit at the harness side, and then the O2 side, and verify the path through the adapters is correct. Getting things crossed up, like O2 heater voltage misconnected to the O2's internal sensor ground circuit would not only blow the fuse, but also mean that at least one other wire would have to be connected to the wrong pin on the other side. That would explain both the blown fuse and lack of activity.

[[email protected]]

Unplug both O2s. Key-on, monitor B1/B2 O2 mV readings in scanner. Do they sit at the default 450mV, and no blown fuses?

If all that is normal with the sensors unplugged, you need to identify each circuit at the harness side, and then the O2 side, and verify the path through the adapters is correct. Getting things crossed up, like O2 heater voltage misconnected to the O2's internal sensor ground circuit would not only blow the fuse, but also mean that at least one other wire would have to be connected to the wrong pin on the other side. That would explain both the blown fuse and lack of activity.

The fuse has stopped blowing... o2s plugged in or not.

I am going to start checking the grounds today... starting off with Splice Pack 122 (pic attached...). All the o2s ground back to this point.

SplicePack122.png

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So I have checked the splice-pack, ground g105.. both ends... it all looks good clean.. no corrosion.

Does anyone know what the voltages I should be seeing on the os2 harness connector???

I have included the o2 wiring schematics...

Each sensor connector from the harness side... has the below wires:

B1S1 (drivers side upstream)
Brown... goes to fuse #15
Black... goes to Splice-Pack 122
Purple White... goes to PCM pin #69 (High Signal)
Tan White... goes to PCM pin #29 (Low Signal)


B2S1 (passenger side upstream)
Brown... goes to fuse #15
Black... goes to Splice-Pack 122
Purple... goes to PCM pin #66 (High Signal)
Tan... goes to PCM pin #26 (Low Signal)


SplicePack122A.pngG105-ground-frame.pngG105-ground-block.png

o2-sensor-connector-wiring.pngo2-LowSignal-PCM.pngo2-HighSignal-PCM.png

[blindsquirrel]

screenshot.08-03-2022 09.51.23.png

Since you didn't fix anything but it stopped blowing the heater fuse all by itself, I'd be real concerned that you burned up whatever it was using for its path to ground - and that's likely either the sensor signal or sensor ground in the PCM.

[[email protected]]

screenshot.08-03-2022 09.51.23.png

Since you didn't fix anything but it stopped blowing the heater fuse all by itself, I'd be real concerned that you burned up whatever it was using for its path to ground - and that's likely either the sensor signal or sensor ground in the PCM.

The only thing I change was installing new o2s... ?!?!?

I am going back under it at lunch... Bill Curlee from Corvette Forum gave me some information about this wiring.

I am going to test the Brown (hot) and Black (ground) to splice-pack122) wires... with the ignition on I should see battery voltage(ish) on the brown.

The purple wires are the PCM reference Hots (the tans are the PCM reference grounds) and with the ignition on should show about 450mV on the purples.

Results in a few...

[blindsquirrel]

The 450mV reference voltage is extremely low current, so low that it's affected by even a voltmeter. You need to monitor the B1/B2 voltage in a scanner with the O2s unplugged. Then make sure it can go both low and high - use your fingers as jumper wires to go from a voltage source (the heater ckt is convenient since you're right there) to the signal line, watch the display voltage go to ~1.2v. Then short the signal to ground and watch it go low.

[[email protected]]

Well...

...here are the results.

I tested battery voltage at the battery first... 12.6

With the ignition ON... engine not running...

Then I hooked-up to the o2s connectors underneath the car... both show 12.5ish on the brown wire, black wire as ground.

Then I checked the PCM pairs... both sides show .400mV on the purple, tan wire as ground.

This looks normal to me...

Any guesses? Is my PCM dead? if so why is it still sending the reference 400 mV?

[[email protected]]

The 450mV reference voltage is extremely low current, so low that it's affected by even a voltmeter. You need to monitor the B1/B2 voltage in a scanner with the O2s unplugged. Then make sure it can go both low and high - use your fingers as jumper wires to go from a voltage source (the heater ckt is convenient since you're right there) to the signal line, watch the display voltage go to ~1.2v. Then short the signal to ground and watch it go low.

When you say scanner, do you mean like HPTuners? The other steps, I am not understanding???

[blindsquirrel]

You need to apply voltage (through your body acting as a current-limiting resistor to protect the PCM internals) to make the displayed O2 voltage go UP from the default 450mV (it will max out at around 1.2 volts). Then apply a ground to see it drop to near zero (some very small number of millivolts, less than 10). It's called testing a circuit.

It doesn't really matter what the voltage is if the PCM can't read it, does it? So driving an input like this high and then driving it low and monitoring the PID in a scan tool lets you check the wire integrity and the PCM's ability to decipher things all in one step.

[[email protected]]

You need to apply voltage (through your body acting as a current-limiting resistor to protect the PCM internals) to make the displayed O2 voltage go UP from the default 450mV (it will max out at around 1.2 volts). Then apply a ground to see it drop to near zero (some very small number of millivolts, less than 10). It's called testing a circuit.

It doesn't really matter what the voltage is if the PCM can't read it, does it? So driving an input like this high and then driving it low and monitoring the PID in a scan tool lets you check the wire integrity and the PCM's ability to decipher things all in one step.

I haven't done this yet... I understand now what you are saying... start scanning.. then use my body electricity to activate the PCM (on the High Signal\purple wire) and hopefully show that change in the scanned o2 voltages ... to prove the PCM is still functional and responding.... I will get that done tomorrow.

...but I did put the old o2wire adapters back in... trying to reverse the first thing that started the fuse blowing.

Now strangely the driver side o2 still sits at 450ish mV but now the passenger o2 stays at 3ish mV. Which is how is was doing before I swapped in new adapters. I let it idle until 185 coolant temp, to see if it would go into closed-loop. No luck, stayed open-loop. And now I get a different message on the scanner (I included the log). I am seeing a "Fuel System #1 Status (SAE) OL - Fault". Previously this showed "OL Not ready".

I thought OL Fault was normally something that happened from large cams, mine is factory.

3-8-2022.hpl

[2xLS1]

OL Fault. The fault is the O2 staying at 450mv. It has to see O2 activity to switch to closed loop.

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IF this becomes a need for a PCM replacement... What kind of train wreck is that? Anyone want to recommend a place to buy a PCM?

[2xLS1]

The only train wreck on a 02 Vette is where GM put the PCM. Below the battery and have to access it through the wheel well/inner fender. The PCMs for that vehicle can be had used for $20 around here. Any 0411 PCM will work. Just have to flash it with the calibration for your car. You will have to license the used PCM regardless of what calibration is in it. Then just write entire the calibration from your original PCM. Since VATS on a Vette is Serial you will have to do a 30 minute VATS relearn.

[[email protected]]

The only train wreck on a 02 Vette is where GM put the PCM. Below the battery and have to access it through the wheel well/inner fender. The PCMs for that vehicle can be had used for $20 around here. Any 0411 PCM will work. Just have to flash it with the calibration for your car. You will have to license the used PCM regardless of what calibration is in it. Then just write entire the calibration from your original PCM. Since VATS on a Vette is Serial you will have to do a 30 minute VATS relearn.

Thanks for the info... guess I will start researching all this now.

You wrote I would have to license the "new" PCM... even if I am using the same VIN? Is that just a license purchase off the HpTuners web page?

Thanks Again...

[2xLS1]

You always have to have a license for what is in the PCM and what you are writing to it. Usually those are the same. With a used PCM it will have something different in it so you will have to license it. Even if you had someone flash the used PCM with your vehicle's factory calibration it would still have to be licensed again because it is a different box.

[[email protected]]

You always have to have a license for what is in the PCM and what you are writing to it. Usually those are the same. With a used PCM it will have something different in it so you will have to license it. Even if you had someone flash the used PCM with your vehicle's factory calibration it would still have to be licensed again because it is a different box.

Thanks for the reply...

Turns out I have 2 unused credits (out of the original 8 from purchase)... 2 will be enough to license a replacement 2002 C5 PCM.


I see I have 4 upgrade credits also, listed in License Info (License Upgrade Path)... could I combine those 4 to the 2 not used and license all 2002 C5 Corvettes?

Thanks...

[Shnraines]

Are the new O2s the same as the originals? I just had where the plug was the same but wires were in different locations in plug. I had stuck at low mv until I checked wires and realized they were different than original. Need to verify heater wires through adapter to heater and same with signal.