411 Not Reading O2 Sensors

**tpichevelle** · 01-09-2023

Hello:

My 411 application to my 350 Chevelle is running but I can't read the front O2 sensors. Both read ~450mV and fluctuate by a few mV. The engine starts and is driveable, just open loop. I can read engine temp, IAT, maf, map, rpm, spark advance, vss, and I hooked up the single wire prndl. I swapped the coil and injector wires for the gen 1 firing order and reassigned the cylinders to the O2 banks. The only thing not hooked up are the knock sensors. It runs rich and I can smell it. Took it on a drive and it runs great. It is more powerful than TPI: more responsive and more powerful. Idles a little rough especially after startup and gets smoother warmed up.

Plugging on a spare O2 sensor connector (chopped from an old O2 sensor) I was able to confirm 12V and good ground wires to the heater. Both sensors get warm to touch after two min so the heaters are working. Heater 12V and ground are hard wired and not controlled by the PCM. The two sensor wires go to the PCM blue connector pins: B1 S1 -PPL/Wht 69, +Tan/Wht 29. I ohmed the wires from the cutoff connector back to the blue connector pins and had good continuity. I grounded both 69 and 29 and reading didn't change, still fluctuating around 450mV. Jumped 69 and 29 together and reading didn't change. I didn't apply voltage since it's a low voltage circuit. The O2 sensor acts like a battery varying it's voltage to the PCM. The PCM is supposed to be like a voltmeter reading the O2 sensor. Tieing the 69 and 29 wires together should make near 0mV. This is the part that makes me question the PCM functionality.

I'm wondering if there is a setting in the bin to make the PCM read the voltages for 69 and 29? It seems like it should be something simple. The same thing happens on Bank 2.

I have a 2nd 411 PCM loaded with the same OS and bin. Same behavior. So what else is it: sensor, harness, and PCM eliminated?

I'm using an AVT 852 cable and AVT LS1 DPID V1.06-aldldroid.adx with tunerpro5.

Maybe someone went through this and knows the answer. Searching found the same issue but no root cause with others. Maybe this write-up can be a reference for others.

Take care,

TPIChevelle

**Fast355** · 01-09-2023

Originally Posted by tpichevelle

Hello:

My 411 application to my 350 Chevelle is running but I can't read the front O2 sensors. Both read ~450mV and fluctuate by a few mV. The engine starts and is driveable, just open loop. I can read engine temp, IAT, maf, map, rpm, spark advance, vss, and I hooked up the single wire prndl. I swapped the coil and injector wires for the gen 1 firing order and reassigned the cylinders to the O2 banks. The only thing not hooked up are the knock sensors. It runs rich and I can smell it. Took it on a drive and it runs great. It is more powerful than TPI: more responsive and more powerful. Idles a little rough especially after startup and gets smoother warmed up.

Plugging on a spare O2 sensor connector (chopped from an old O2 sensor) I was able to confirm 12V and good ground wires to the heater. Both sensors get warm to touch after two min so the heaters are working. Heater 12V and ground are hard wired and not controlled by the PCM. The two sensor wires go to the PCM blue connector pins: B1 S1 -PPL/Wht 69, +Tan/Wht 29. I ohmed the wires from the cutoff connector back to the blue connector pins and had good continuity. I grounded both 69 and 29 and reading didn't change, still fluctuating around 450mV. Jumped 69 and 29 together and reading didn't change. I didn't apply voltage since it's a low voltage circuit. The O2 sensor acts like a battery varying it's voltage to the PCM. The PCM is supposed to be like a voltmeter reading the O2 sensor. Tieing the 69 and 29 wires together should make near 0mV. This is the part that makes me question the PCM functionality.

I'm wondering if there is a setting in the bin to make the PCM read the voltages for 69 and 29? It seems like it should be something simple. The same thing happens on Bank 2.

I have a 2nd 411 PCM loaded with the same OS and bin. Same behavior. So what else is it: sensor, harness, and PCM eliminated?

I'm using an AVT 852 cable and AVT LS1 DPID V1.06-aldldroid.adx with tunerpro5.

Maybe someone went through this and knows the answer. Searching found the same issue but no root cause with others. Maybe this write-up can be a reference for others.

Take care,

TPIChevelle

What harness are you running?

I ran across this once in a friend of mines car. Another mutual friend of ours had converted a DBW P59 harness to a DBC 0411 setup. He did not follow the O2 sensor changes for Case vs Isolated Case grounded sensors. The 02s would default to 450mv and eventually the PCM would show Open Loop/Error status. Once we discovered the wiring had not been corrected, we went to the wrecking yard, grabbed a DBC P59 from a Van and started over. As soon as the P59 went in that matched the 02 sensor wiring it went into closed loop and ran great.

FWIW 450 mv is DEFAULT on the 02 sensors when the PCM is not reading them usually due to incorrect wiring. I cannot recall what these PCMs do if you have Open Loop Enable flag set to keep them in Open Loop full time. I know that some were setup that way Export for Leaded Fuel. Normally if the 02 sensor is simply not ready, the 02 voltage will read what the sensor is reading, in the 30-50mv range.

**Fast355** · 01-09-2023

Forgot to also mention, having the 02 sensor heater power and ground hard wired is not an issue. My 97 Express van came from the factory with all 4 sensors wired that way and I have since swapped it to a P01 0411 and then to a P59 and it has remained wired that way. PCM is only wired to the 02 sensor signal and signal ground wires. In the P59, I had to turn off 02 sensor heater codes, but the sensors still work and it goes into closed loop quickly.

**tpichevelle** · 01-09-2023

Thanks for the reply. This is a Painless Performance harness, new. I'll look into turning off the heater codes. I don't have a check engine light. The Open Loop Enable is not set.

**tpichevelle** · 01-09-2023

Adding PCM info from PCM Hammer 021:
AVT 852 Reset OK
[10:18:43:330] AVT Firmware 4.7
[10:18:52:946] VIN: 2G1FP22G422152739
[10:18:53:042] OS ID: 12212156
[10:18:53:066] Hardware Type: P01_P59
[10:18:53:162] Calibration ID: 12208511
[10:18:53:266] Hardware ID: 9386530
[10:18:53:450] Serial Number: 1EB0UQSE0355
[10:18:53:562] Broad Cast Code: DLAC
[10:18:53:658] MEC: 0

**tpichevelle** · 01-10-2023

Solved it!!!!

The Painless 1999 - 2002 GM VORTEC FUEL INJECTION 4.8L, 5.3L & 6.0L WIRE HARNESS INSTALLATION INSTRUCTIONS Manual P/N 90530 is wrong. They specify O2 sensors Delco AFS106. These sensors are incompatible with a floating reference. For this harness, the sensors have to have an internal ground. These sensors have a floating ground. This is why they act as if disconnected. I'll explain.

The heaters on the O2 sensors are powered and grounded outside of the PCM. Therefore the 12V and ground are external to the PCM and do not go through the blue or red connector. The two wires from the sensor go to the blue connector. The tan and tan/wht wires are the negative and the purple/purple/white positive. The tan wires have to be grounded for reference either by the harness or the O2 sensor. This is why the response of changing the harness worked. There was also a thread where someone jumpered the tan wires to ground and it worked. This is why sometimes when people change the O2 sensor it worked, as long as they used an internally grounded unit.

Notice the circuit diagram from another thread shows the internal grounds.

My solution was to jumper the tan wires to pin 40 ground wire. Now touching the purple wires to the tan wire at the 02 connector causes the 445mV to go to 0mV. When the O2 sensors head up, they go to 30mV in open air. The 445mV occurs because both the tan and purple inputs to the PCM have a resistor divider. When there is no senor or ground reference the resistors hold he input to 445mV. I attached the diagram with the red circles to highlight the internal sensor grounds.

Tomorrow I can continue toward closed loop.

Take care all,

TPIChevelle