Troubleshooting PCM - Torque App - BAFX adapter

[TA_C10]

Guys I have reworked my own harness using OEM harness and PCM. My harness is from an 05 with blue green connectors. PCM has been reprogrammed by brendan at LT1swap.com

I am using a BAFX bluetooth module in the OBDII port using the TORQUE PRO app to try and read the PCM. As far as I can tell the PCM is getting power, I tested both pin 19-20 on blue connector using ohm meter with less than 4ohm on both the ground and power pins.

The torque app is not able to read the PCM for some reason... Any help would be appreciated. Right now I am supplying 12v from battery straight to the fuse box for battery hot connections. This successfully powers on the OBDII port and is supposed to supply constant PCM power. 15amp fuse between. Then I am using 12v battery source to power on a relay which then feeds the rest of the harness power which includes pin 19 for PCM ignition which is key hot.

Why would the bluetooth adapter not be able to read the ECM? It powers on and attempts to read it but never finds it as it searches all the protocols.

[TA_C10]

Oh yeah, one more thing. When I supply power to just the battery hot stuff(not the key hot stuff) I check voltages and battery constant hot is fine with 12 volts, but somehow 9.7 volts shows up on all the key hot stuff before I power the relay(key hot). Is that supposed to happen?

[Wildkarde]

you should have constant hot on pins 20 and 57 of the blue connector. Ignition hot on pins 19 and 75 blue. and 8 seperate ground wires. B 1-24-27-40-64-67, G 1-40.

The way you described testing pins 19 and 20 in your first post makes it seem like you didnt get all those wires.

Also your oicture doesnt seem to be working.

[TA_C10]

Originally Posted by Wildkarde

you should have constant hot on pins 20 and 57 of the blue connector. Ignition hot on pins 19 and 75 blue. and 8 seperate ground wires. B 1-24-27-40-64-67, G 1-40.

The way you described testing pins 19 and 20 in your first post makes it seem like you didnt get all those wires.

Also your oicture doesnt seem to be working.

Thanks, I fixed the picture in post 1. And I have tied all the grounds together into 3 eyelets at the rear of the engine. I have them installed in the back of passenger head. I tested all the grounds. I pinned out 20 and 57 with battery hot and they were getting 12.5 volts just fine. Then I hit the ignition relay for key hot and pin 19 was getting 12.5 volts. I have a funny feeling everything is working fine but the bluetooth adapter. I actually have 2 different kinds of adapters and neither of them are able to connect to PCM. I am thinking maybe its the OBDII wiring pehaps? I dunno. I am going to pin them out tomorrow to make sure.

And where is pin 75 supposed to be? Key hot? Battery hot? I don't remember this one... I see its off/run/crank voltage, so is this key hot constant power? Or something else?


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[Wildkarde]

blue 75 is the other keyed hot.

Maybe check your adapter on you daily driver car just to make sure it works.

How do you have the obdii port wired. should be at least 3 wires, hot, data, ground, at the least, and its a good idea to hook up the other ground as some older scanners use it.

[TA_C10]

Ok guys, pinned out a lot this morning. Not finding any issues except fuel pump relay trigger wire(more on this later).

All the PCM grounds in the PCM have an Ohm rating of 52. All the grounds outside of the PCM have a Ohm rating of .01-.03

Pin 19 and 75 have 12v key hot
Pin 20 and 57 have 12v battery hot

Pin 58 class 2 serial data Ohm's out .02, and when battery hot is on, no DC voltage, but when key hot is applied it shows a tiny bit of voltage. This one is plugged into OBDII port #2

OBDII port 4-5 are both ground and they Ohm out good.
OBDII port 16 is hot 12v with battery hot applied.

Now this is a different problem I found. Seems my fuel pump relay doesn't kick on when I apply key hot 12v. Green connector pin 9 Ohm's out fine at the relay block connector. When I apply batt hot, no voltage on pin 9. When I apply key hot, pin 9 only see's 1.16 volts, and this is constant 1.16 volts, it doesn't cycle. Is this a problem?


So to recap:
Problem 1: Looks like all pin outs are working fine as far as I can tell but OBDII connectors(2 different kinds) can't read the PCM serial data.

Problem 2: Fuel pump not working. Pin 9 green connector not supplying 12v, only 1.16 volts yet it Ohm's fine at .01


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[Wildkarde]

It sounds like you have all the power and grounds wired correctly. The fuel pump will only cycle for a few seconds when you turn the ignition on unless you start cranking the engine. The wire at pin 9 should go hot to trigger the relay. Can you jumper the relay and make the pump run? If so it sounds like there might be something wrong with the ecm.

[Wildkarde]

One other thing, i assume this is electronic throttle being a 05, does the throttle body cycle when you turn on the "ignition" wires?

[TA_C10]

Originally Posted by Wildkarde

One other thing, i assume this is electronic throttle being a 05, does the throttle body cycle when you turn on the "ignition" wires?

Yes it does actually. I'm not sure what a proper cycle is but every time I hit the key on power the throttle body kicks and tightens up. Then when I unplug the key hot it clicks again. It has an annoying electric whine/squeal the whole time key hot is plugged in gonna have to find out why. The DBW pedal doesn't do anything but I assume that's because it's not running.

Right now I'm not using the key ignition btw, I have just put spade connectors on one end and on the battery I have the female ends, and I plug the battery hot in first, then I plug the key hot in second. I assume this is ok.

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[TA_C10]

I made an edit to that last post FYI.

[Wildkarde]

honestly at this point, i am leaning pretty heavilly on something being wrong with you ECM. Did you ever check your obdii adapter and torque on another vehicle? Do you have anyone nearby that has an vehicle you could swap a ecm from, it wouldnt have to match your engine exactly, just be a blue/green gen 3 ecm to at least make sure you have the power/obd stuff working right.

[TA_C10]

I did some more testing tonight. I found out that the secondary fuel pump (green pin 3) in PCM(i removed this wire from harness) is getting 12volts when i plug in the key hot power. But the primary fuel pump (green pin 9) is not. Is primary green pin 9 supposed to have 12 volts constant when key hot is on?

Secondary green pin 3 doesn't give 12 volts for 2 seconds and cycle off, it just has constant power. I'm not sure if its acts the same as the primary but I would think it would right?

Also, I checked the yellow wire for MAF sensor wire (green pin 31) and it too gets 12v at key hot. But the sensor wire for OBDII only gets like 1.16v... I was just thining that all these sensor wires i thought were supposed to get 5v references not 12v... I also checked blue pin 48 MAP sensor 5 volt reference wire at the PCM and its not getting 5v only 1.16 or 1.61 whichever it was. Regardless its not 5v like the diagram pinout from LT1swap.com says.

I wish I knew better what I was doing. Some of this makes sense to me but some of it isn't quite sinking in yet so i don't fully understand how this PCM works to troubleshoot it with confidence.

My neighbor has silverado, i think its a 2003 so should work but its whether or not he will let me take the PCM out or not, he may not like that idea we will see.

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[TA_C10]

I edited post 12. After re-reading the first paragraph it was confusing so I fixed that. I need to start reading my post before I hit the submit button.

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[TA_C10]

And the neighbors silverado is a 2002 so that won't work. 1 year off. His will be blue and red connectors on PCM if I am correct.

[TA_C10]

I connected my bluetooth adapter to my neighbors OBDII port(2002 silverado) and its working fine. Connected to the PCM without issue. Not sure what else to do to figure out if my issue is the PCM or something else. I don't have HP Tuners or anything to read PCM, just a bluetooth adapter.

UGH!!

[Wildkarde]

Some replies to post 12, pin 9 should get +12v for 2s when you initially power up the ecm then go off. If the computer senses the engine cranking it will keep the pump on. Not sure about the secondary tank wire, i;ve never dealt with it before, but i would be supreised if it was supposed to stay hot all the time like that.

As for the sensors, some like the maf sensor just get 12v from the fuse panel and others like the map and throttle position sensors get regulated 5v. The fact that you aren't getting the 5v reference for the map is another point in the somethings wrong with the computer box. What about blue pin 2, and green 39, those should have a 12v reference on them, so right at 12v not 13.6 or whatever your battery is actually putting out.

The signal wire on the obdii port is high frequency data, so the voltage reading on a meter is gonna be all kinds of weird.

The fact that the obdii adapter works, especially on another similar era gm is troublign for you ecm. One last thign I can think of for you to try. Unplug the blue ecm connector and test and make sure you have good continuity between blue 58 and pin 2 on the obdii port. Like single digit ohm value, lower the better.

[TA_C10]

It was a ground issue! Took the ECM to a local LS shop here in Ft Worth and the ECM was good. I took them my harness too and it took him 5 min to figure out a ground issue. He ground the case of ECM and got full power and all was working.

So I brought it home, traced blue connector 1 and 40 ground wires back in harness and sure enough when I did my grounds in harness I actually ran the main junction ground back to the MAF sensor instead of out to an eyelet .... So I tied that wire in with the big junction of ground wires in harness and boom, problem fixed.

And it lives!!!

C10 First Start - YouTube

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[Wildkarde]

Nice, glad it was a something liek that, finding "good" used ecms can be a pain, and new ones are even worse if you dont know someone with access to a techII.