I have a mail order tuned F-body PCM and a 2004 GTO harness. One of the problems so far is that the O2 sensors on the harness are ground through the PCM for the GTO. The F-body computer's harness would use a chassis grounded O2 sensor. That is about as much as I have found with the search.

I have an email in to the tuner but the quicker I can get an answer the quicker I can get this motor started.

My question is can the F-body PCM be programmed to work with the GTO's harness's O2 sensors?

 

Nope, the f-body pcm is the older 512k red and blue connector pcm. The GTO has the newer 1mb green and blue PCM.

You can use that harness, but you will have to rewire it to the same pinouts as an f-body harness. Not too hard, but it will be a couple hours of re-pinning connectors. The change in the O2`s is that the GTO pcm is designed to provide the grounds for the sensors where as in the f-body they were just grounded to the block.

 

Thanks, for your help. I have found that the blue connector pin 42 on the 2004 GTO PCM can be turned on for the low speed fan relay. I found a thread that said a new version of a tuning software would allow the green/blue connector to turn on A/C request. If that is the case, I can use the harness as is with the GTO PCM. Can anyone confirm this?

 

If you have a RED/BLUE connector PCM, you CAN use this pcm on a 03+ harness (GREEN/BLUE connector) with cable throttle, with a few simple modifications. The only thing that needs changed, other then what was talked about above, is some of the oxygen sensor wiring. On the 2003+ blue/green connector PCM's, the PCM supplies a GROUND for the oxygen sensor heater's, and 12v+ comes from the fuse block. In the 99-02, power and ground is fed directly to the o2 sensor heaters. To make the changes needed to 2003+ blue/green harness, to work with a blue/red computer is this:

REMOVE: BLUE PCM connector pins: 24,27,64,67. These should all be black with white stripes. These were extra ground wires provided to the 03+ pcm so it could control ground to the o2 heaters. The 99-02 pcm does not need these. Just pull the pins out, don't cut anything yet, we need to hook these to a few other wires we pull out of the PCM connectors.

Next we need to remove the wires from the PCM connector that go to the oxygen sensor heater control. There are 4 wires, one for each oxygen sensor. If you are only using front oxygen sensors in you conversion, omit anything to do with Sensor 2.

Bank 1 Sensor 1 - BLACK/WHITE - GREEN connector pin 72

Bank 1 Sensor 2 - BROWN - GREEN connector pin 52 - after CAT o2 sensor

Bank 2 Sensor 1 - LT GREEN - GREEN connector pin 74

Bank 2 Sensor 2 - RED/WHITE - GREEN connector pin 53 - after CAT o2 sensor

Now, you should have 4 ground wires, and 2 (or 4) oxygen sensor heater control wires pulled from the PCM connectors.

You need to locate the 4 tan oxygen sensor low reference wires going into the BLUE pcm connector. If just using front o2 sensors, its BLUE pins 26 and 29. If also using rear o2 sensors, add pins 25 and 28. These wires will always be TAN and may have a white stripe. The easiest way I can think of to splice into these, is pull the pin out (REMEMBER WHERE IT GOES BACK) remove some insulation with a knife, solider on a wire, and slip some heat shrink up and past the terminal and shrink the heat shrink down over the splice. Then reinstall the pin in its original location. Leave about 12" of wire loose for each wire you splice into. Do this for all the o2 sensors you will be using.

So at this point. You should have 4 black/white ground wires loose. 2 to 4 oxygen sensor heater control wires loose, and 2 to 4 wires going to each of the TAN wires. All of these wires need hooked together in a big splice pack. First get some larger heat shrink, 1/4 or 5/16 should work. Put about 4 inch long piece of heat shrink over all 4 ground wires. Next strip off about 1-2 inches of insulation off all your wires. Start hooking them together end to end, you should be able to solider all these together, and slip the heat shrink over when done.

The last step, is to make the connectors fit inside the PCM. This will require cutting the rib off the GREEN plastic terminal cover, so it will fit in the RED pcm socket.

You will need to use oxygen sensors for a 2002 chevy truck, 5.3L, will be a white plastic connector, and will plug right into the 03+ harness without changing plugs.

That is it. To understand WHY we had to hook in the TAN wires, please read the OXYGEN SENSOR info page.

*****If you found this page helpful, please let me know, by all means. lt1swap@centurytel.net

 

Thank you, that was very helpful. There are a couple of others in the same position I am in with the harness and PCM. I will send that to them.

 

Glad I could help, I had to use the same info for my swap, but the credit should go to Brendan, his website is www.lt1swap.com which has plenty of wiring info.

 

This place is awesome! Good job

 

Well, I am going to stay with the original harness and ECU. Now I have another question. Can anyone confirm the ignition 3 voltage wire is switched? It is an orange wire but the schematics show it going to the ignition so it would be hot in run and start like a pink wire. Can anyone confirm this?