Needing help with PCM connectivity 01 ST

[SKW1020]

I’d have to go outside and take one apart but I can show you it’s pretty obvious pcm side and dash/ truck side

View attachment 463240

Well, I am sure I am doing it right, but I get no continuity, or ohms from any of the pins you have specified..... nothing. From OBD2 to the C115 to the PCM is that crazy or what?

 

[410Fortune]

Something fishy about your tests
You should for sure have connectivity somewhere
Unhook battery - terminal
Unhook pcm connector
Unhook c110

Make sure you are on correct pins the connectors have tiny numbers on them

Try simple continuity test between pin 15 at the pcm connector and a in 3 at c110
Same with 16 and 11

You should get a tone / zero out on the meter

Make sure you are on the right pins and wire colors
There is no way that both of those wires are broken inside the stock harness

 

[SKW1020]

Something fishy about your tests
You should for sure have connectivity somewhere
Unhook battery - terminal
Unhook pcm connector
Unhook c110

Make sure you are on correct pins the connectors have tiny numbers on them

Try simple continuity test between pin 15 at the pcm connector and a in 3 at c110
Same with 16 and 11

You should get a tone / zero out on the meter

Make sure you are on the right pins and wire colors
There is no way that both of those wires are broken inside the stock harness

Ok.. dumb question: Which is the C110 connector? Is it the 42 pin plug thats on top of the valve cover by the distributor?

 

[410Fortune]

Yes

 

[SKW1020]

Ok.. dumb question: Which is the C110 connector? Is it the 42 pin plug thats on top of the valve cover by the distributor?

Ok just looked at the back of the PCM wiring and the wires on my pcm are like this:

Pin14 - Pink/gray
Pin 15 - tan/white
pin 16 - gray/white
pin 17 - light blue/pink

This looks nothing like the diagram I am looking at. Idk wtf is what lol

 

[SKW1020]

Yes

Ok, I just went and checked every pin on the pcm with my other lead attached to the #2 pin on the OBD2 port. I got 1 connection and it was pin # 90 and did the same thing with my lead on the #10 pin on the OBD2 port and I got one connection and it was pin #91

 

[410Fortune]

What is the build date of your 01 trac?

Good job!

 

[410Fortune]

Something again is fishy
Pin 2 is tan with orange scp bus +
( as we have established)
It should only have connectivity to pin 11 at c110 and pin 16 at the pcm connector

I’m just checked my 02 sport trac book and all the pin locations are the same

So somewhere in your wiring you apparently have a short

Pin 90 is brown with white reference voltage

Pin 91 is at the pcm are
Sensor signal return (grey with red)
This wire goes all over the place to many engine sensors

Neither of these wires should have any connection to pin 2 at the obd2 port

Has any of your wiring been messed with swapped or? Any rodent damage?

 

[SKW1020]

Something again is fishy
Pin 2 is tan with orange scp bus +
( as we have established)
It should only have connectivity to pin 11 at c110 and pin 16 at the pcm connector

I’m just checked my 02 sport trac book and all the pin locations are the same

So somewhere in your wiring you apparently have a short

Pin 90 is brown with white reference voltage

Pin 91 is at the pcm are
Sensor signal return (grey with red)
This wire goes all over the place to many engine sensors

Neither of these wires should have any connection to pin 2 at the obd2 port

Has any of your wiring been messed with swapped or? Any rodent damage?

Ok I have a correction: I have continuity between pin #2 on the OBD2 port and Pin#89 on the PCM and I have Continuity between pin #10 on the obd2 port and pin#90 on the pcm NOT 91. the wire on my pin#90 is LB/PK. The wire on pin 89 is tan/orange.

A couple years ago a friend of mine tapped the wire for the TPS which I removed.... and 3 years ago, because a friend wrecked it for me I was cutting the radiator support and cut every single wire in the harness underneath it. However, i painstakingly reconnected them, and no issues whatsoever until the other night... when it cut out as if I'd turned off the ignition. No rats eating that I know of. Creation date was 09/00.

Knowing none of these wires have really been messed with, it throws me that the pin 90 wire should be brown/white when its lb/pk?

 

[410Fortune]

Here is the schematic for the obd2 port (data link connector)

As you can see the wires go directly from the obd2 port through 3 connectors only
C146 (firewall bulkhead connector under your brake booster)
C110 (42 pin square) and c175 (the pcm)

You should not have continuity to wires 89 and 90
89 is circuit 355 grey w white throttle position sensor input
90 is 351 brown w white reference voltage

You do have the pcm unplugged for wire checking?

Many of the wires that were cut after your accident carry power, if there was a dead shirt in your previous repairs it can have repercussions in the wiring system, like short out a pcm, blow relays and fuses
Etc which is why we must first test your wiring
Maybe look at previous repair area and make sure all is still good

Circuit 914 at obd connector should only have continuity through the 3
Connectors
Listed and the pcm
Same goes for 915. As you can see they don’t branch off to other locations (except pats module behind pass airbag)

 

[SKW1020]

Here is the schematic for the obd2 port (data link connector)

As you can see the wires go directly from the obd2 port through 3 connectors only
C146 (firewall bulkhead connector under your brake booster)
C110 (42 pin square) and c175 (the pcm)

View attachment 463280

View attachment 463281

You should not have continuity to wires 89 and 90
89 is circuit 355 grey w white throttle position sensor input
90 is 351 brown w white reference voltage

You do have the pcm unplugged for wire checking?

Many of the wires that were cut after your accident carry power, if there was a dead shirt in your previous repairs it can have repercussions in the wiring system, like short out a pcm, blow relays and fuses
Etc which is why we must first test your wiring
Maybe look at previous repair area and make sure all is still good

Circuit 914 at obd connector should only have continuity through the 3
Connectors
Listed and the pcm
Same goes for 915. As you can see they don’t branch off to other locations (except pats module behind pass airbag)

it makes me think that I'm reading the pcm backwards and upside down because the positions are exactly flipped and reversed from the way I've observed it. Pin 89 and 90 are exactly same position as pin 15 and 16 but mirrored and flipped... how am I reading it so wrong? The diagram I am looking at tells me that its pin 89 and 90. I dont get it. And on my diagram, pin 15 and 16 are the colors that pin 89 and 90 are supposed to be. Here is the one I am looking at:

 

[SKW1020]

it makes me think that I'm reading the pcm backwards and upside down because the positions are exactly flipped and reversed from the way I've observed it. Pin 89 and 90 are exactly same position as pin 15 and 16 but mirrored and flipped... how am I reading it so wrong? The diagram I am looking at tells me that its pin 89 and 90. I dont get it. And on my diagram, pin 15 and 16 are the colors that pin 89 and 90 are supposed to be. Here is the one I am looking at:

View attachment 463289

I'll go look at all of those splices, but theyve been good for 3 years.

 

[410Fortune]

On your pcm connector there are numbers for the pins, very tiny, but they are there.
Always locate pin 1 on the actual connector when comparing to diagrams

You are simply looking at the wrong side of the connector

If you had it reversed then no need to check the old wiring
Now you just need to perform the connectivity tests

 

[SKW1020]

On your pcm connector there are numbers for the pins, very tiny, but they are there.
Always locate pin 1 on the actual connector when comparing to diagrams

You are simply looking at the wrong side of the connector

If you had it reversed then no need to check the old wiring
Now you just need to perform the connectivity tests

Well son of a you know what.... I looked and voila, there are the numbers right on the BACK of it.... how dumb is that? Thank you for showing me the obvious. I'll retest

 

[410Fortune]

Man don’t worry about it, unless you do this everyday how would you know. Pin 1 often has a big ass wire in it, so once you see that you will always know where one is, this is true for Most of the big multi wire plugs

Getting orientated is part of the deal

 

[SKW1020]

Man don’t worry about it, unless you do this everyday how would you know. Pin 1 often has a big ass wire in it, so once you see that you will always know where one is, this is true for Most of the big multi wire plugs

Getting orientated is part of the deal

Indeed, and next is finding the time to do the work... I plan on doing the testing tonight. Thanks for all youve done my friend, I appreciate it.

 

[410Fortune]

No problem let’s get this fixed

 

[SKW1020]

No problem let’s get this fixed

Ok, you said to start with a simple continuity test by testing the scp bus + and - from OBD2 to the pcm pins 15 and 16. There is continuity.

Then you said to verify ground at pins 24, 25,51 and 103 and assuming this meant to plug a wire in the obd2 port 3 or 4 (ground) and then do a continuity test at these pins, then yes, they all are grounded.

I dont understand what you mean by verify power at the pcm connector with the key off pin 55.... is this a voltage check? I get no voltage from pin 55 with the key off.

And then with the key on you said pin 71 and 97... not sure where to put my other lead when I do this.

 

[410Fortune]

Nice!! So the communication wires are connected from port to pcm

The issue is no start and Your scanner will not talk to pcm
So the thought process here is your pcm may not be getting powered up. Now that we know the can bus wires are connected from obd2 port to pcm, we can shift our focus to the pcm not getting powered/ working

So you are going to check pcm power feeds

When you turn the key the ignition switch powers/triggers the pcm/eec relay. It does this through an interior fuse (19) then through the power diode in the pjb (power junction box = fuse box under the hood) and then finally to the relay
The relay then sends battery power to the pcm and several engine sensors (injectors, coil packs, etc) via the red wire. This is vpwr circuit

So you want to check the grounds, which you did. The ground wires at the pcm should have continuity to ground

Now you are going to check the power side of the pcm
So to do a power check, basically test for battery voltage. Put your multimeter ground lead on the - at the battery terminal and the + red wire probe is your tester

First test pin 55
This should be power all the time. Keep alive power, battery voltage constant to pcm

Next test for power at the other power feeds, this time with the key turned to run
You should have battery + voltage at pins
71 and 97

 

[410Fortune]

Pin 55 should have power with the key off

Since it does not then first
Is the battery hooked up? lol
Is c110 connected?

Fuse 1.21 in the under hood power dist box feeds pin 55 pretty much directly
Notice it goes through connector c110

Now you need to inspect that fuse and wire and find out why pin 55 has now power

You fix this you likely will have a running truck and a scanner that will communicate