Truck is a 96 S10 Extended cab, originally a 4.3 Vin X 5 speed, Z85 suspension, non ZQ8 with factory 8.5 rear axle. We have swapped in a 408LSx T56 using a Current Performance harness and have removed the ABS entirely so the stock ECM is no longer around.

The truck is running and driving, no CEL, i have power and ground at the OBD2 port and i have continuity between pin 59 on the ECM and pin 2 on the OBD2 connector. With the harness connector installed into the ECM, i also have continuity to pins 4 & 5 on the OBD2 port which are chassis and system grounds respectively, and also pin 8 which is CCM diagnostic. With the ECM plug removed from the ECM i only have continuity to between pin 59 and pin 2.

My question is, would this be considered normal. Ive gone as far as cutting the harness wire at pin 59 and pin 2 and connecting a jumper wire between the two completely bypassing the wiring harness altogether and i am still not able to get serial data on pin 2.

I removed the dash to replace the heater core, and in the process of putting everything back together there is a junction block on the passenger side of the dash behind the glove box, one of the wires got pinched between it and the metal mounting bracket, when i first hooked up the battery to try and start the truck one of the fusible links on the drivers fender junction block blew. I wasn't sure what this link controlled since they aren't labeled, but the truck cranked over but wouldn't start. I had no power to the fuel pump or ECM, i applied power to the fuel pump bypass plug and it powered up just fine but still wouldn't start. After a few days of retracing my steps i found the pinched wire, fixed it, replaced the fusible link and the truck fired right up. But its not running to great since the tune isn't 100%.

As far as can tell the pinched wire didn't cause any other problems, but im wondering if it somehow is the cause of us now not being able to link to the ECM thru the OBD2 port. With the ECM out of the truck and on the bench, Nelson can connect to it just fine.

If i cant come up with some options to check, or somebody that has maybe had this problem before im going to have to remove the harness and send it back to Current Performance for them to check it out. Something somewhere is blocking the data signal is what i think, cause if i have continuity on the circuit, i should have data connection as well.

Thoughts, Comments?

Thanks for any and all help.

 

Bueller...Bueller...Bueller???

 

Make sure you have 12 volts at pin 16 of the DLC

 

I do, first thing i checked. Ive ordered a replacement OBD2 plug and it should be here in a few days, hoping that will fix the problem.

 

Serial data from the dlc to the pcm is a single wire only. Cut the wire at the dlc and run a jumper under the hood and slip the serial data wire out of the pcm connector and insert a spare pin into the pcm to hook your jumper up to. This will keep you from have to cut the current performance harness.

What type of scan tool are you using and are you telling it the correct year and vehicle platform the pcm is flashed for.

 

we did cut the harness and attach a jumper wire and it didnt fix the problem. we have tried generic obd2 code readers, and HP Tuners box and nothing can link to the ECM. I pulled the dash out of the truck to completely go thru the wiring harness and found nothing wrong, so i ordered a replacement OBD2 plug and hoping that will fix the issue.

 

But did you completely disconnect the existing harness on both the truck side and the vehicle side from the dlc serial circuit so it is a single wire jumper straight from the dlc to the pcm.

cut at dlc splice jumper run single wire to underhood and use a old pin to splice to then insert that into the pcm serial data pin. What platform is the PCM donor vehicle from. Is it a 12200411 svc number on the pcm or a newer dbw pcm?

 

Thats what we did, completely isolate the serial wire and it still wouldnt connect, but with the ecm on the bench it connects fine.

Installed the replacement obd2 port under the dash and it didn't change anything.

 

What did the donor motor and pcm come out of? Sounds like you have the serial data pin the wrong cavity. It's not a power or ground issue at the pcm because you state the motor starts and runs.

 

Yea, starts and runs fine. PCM is the 0411 style with blue and red connectors and serial data is hooked to pin 59 on the blue connector, tried 58 as well and nothing. Engine was built from scratch starting with an 04+ 6.0L block.

With the pcm on the bench hooked to a benchtop harness at nelson performance they can connect to it just fine and even switched out the pcm for a different one and it didn't change anything.

 

It should be pin 58 on the C1 blue pcm connector and pin 2 on the dlc. Somebody didn't mix up the pcm connectors?

 

Well the guy that built the harness said you can use either 58 or 59 for serial data. But I was looking g at some pcm pinouts this morning is they all showed 58 as serial data and 59 as not used. Ive moved it back and forth to check but with the new obd2 connector im gonna move it back to 58 and see what happens.

 

Blue connector pin 58 is the class 2 serial data location at pcm.

Pin 2 on the DLC is the serial data wire location purple in factory form.

 

Check on both accounts. Switched to pin 58 and still wont link.

 

Are the red and blue covers mixed up? Meaning you are pinned into C2 not C1?

 

no, they are in the correct place, and Ive gone over the harness several times and this just doesn't make any sense.

 

verify all pcm grounds and power as per pinouts.

 

If the engine runs good, but you can't connect with the PCM even if you hook directly to pin 58 on blue connector, you may have a PCM with a damaged communications port.
Put the PCM in another vehicle like the donor car. if you can't connect to it with a scanner, then it is damaged.

You can open it to see if pin 58 is broken from the inside

 

I can hook the pcm to a benchtop harness at nelson performance and connect to it fine.

 

Then you have a bad wire, or the pin at the blue connector isn't touching the pin at the PCM side.
Run a straight wire from PCM to OBD2 port, nothing in between.
Cut the green wire at pin 58, just a few inches from the blue connector, then splice from there to DLC pin #2. Feed the +12V and grounds and test.

If you still can't connect, then you have a bad connector. Buy a new one and change it, it's easy. Just reuse all other pins and change only the 58.