2004 GT - Computer Voltage Question

[tsgman01]

Looking for some help here, (I searched and searched some more and didn't find much). A little background may help you help me.. I have an '04 GT (5-spd) that had some bad wiring done by the previous owner for LED lighting and the interior caught fire basically melting the center console area and the wiring harness. I got the car "as is" and I stripped the interior down to nothing but the steering wheel and got a good harness out of an '03 GT (auto). The new harness is in and I want to start the car to see if there are any gremlins and to verify it runs before putting all the interior back together. I had PATS removed from the computer and I also have a new gauge cluster (out of the same '03) and PATS was keeping the fuel pump from coming on. Before I connect the computer (just got it back from the tuner), I want to verify that the voltage at the computer is correct so I don't fry it when I try to start it or damage something else. I have a pin out diagram and pin 55 (reference voltage supplied at all times - overload protected) and pin 90 (reference voltage) are not showing anything on the volt meter, with the key on at the 2nd position or with the key removed. When I turn the key to the 2nd position the fans come on and I hear relays clicking, but no voltage at the connector. Looking for suggestions as to why there isn't any voltage at the connector. Battery shows just over 12v, and grounds on the harness are connected. No other visible damage to any other wires/connectors and everything that can be connected is (meaning there is no dash/console so the connectors for the radio/heat/lights are not connected). Any assistance on finding voltage to the computer would be much appreciated!

 

[wmburns]

Test for key off power at fuse F2.34, F2,2, F2,8. Should be off.

Now test for key on power in and out of fuse F2.34, F2,2, F2,8 with the key on. Post the results. What to do next depends upon the results.

Recommend using a test light that will "load" the circuit.

1999-2004 MY fuse panel schedule:
https://www.allfordmustangs.com/for...r-swap-wont-fire-please-help.html#post2669271

1996+ Crank with no start check list
https://www.allfordmustangs.com/forums/4-6l-tech/336452-1997-mustang-wont-ignite.html#2984838

Having a full function ODB2 scanner might make short work of some of the deeper workings of your car.

ForScan ODB2 scanner w ELM327 USB
https://www.stangnet.com/mustang-forums/resources/forscan-odb2-scanner-w-elm327-usb.57/

Do yourself a big favor and make sure that the battery and charging system is in tip top shape.

Howto perform charging system voltage drop test
https://www.stangnet.com/mustang-fo...perform-charging-system-voltage-drop-test.56/

 

[tsgman01]

ok, so my results were not what I am sure they should be. Just to recap, the computer is NOT connected in the car. The gauge cluster and all other connections on the wire harness are connected with the exception of those related to the center console.

Meter used: Craftsman 82141
Key on means turned to the 2nd position
Key off means key not in ignition

With Fuses: F2.2, F2.8, F2.34 pulled out, the following occurred:
Key off: No readings on any fuse with the meter
Key on: no readings on any fuse with the meter
Key out: theft light flashes after having turned the key
Key on: no fans running
Key on: I hear relays click
Key on: no readings on cluster

With Fuses: F2.2, F2.8, F2.34 inserted, the following occurred:
Key out: theft light flashes after having turned the key
Key on: fans running
Key on: I hear relays click
Key on: RPM and MPH needles move (but they didn't move each time I turned the key from off to on)
Key on: Odometer reads all dashes
Key on: Air bag light flashes
Key on: Battery light stays on
Key on: fuel level at 1/4
Key on: Battery needle about half way

Thanks for your assistance!!!

 

[wmburns]

Both tests need to be done with the fuses in place. The test is to be done by probing the fuse's "test point" with the testing device.

Note, fuse F2.34 is the pilot duty CCRM circuit from the ignition switch. So what's being tested is IF the ignition switch is powering the pilot duty circuit.

F2.2 and F2.8 are down stream of the CCRM. So what we are testing is IF the CCRM is working.

 

[tsgman01]

Ok, With the key off and fuses in, I get no reading on the meter. With the key turned to the 2nd position I get 11.78 on fuses F2.2 and F2.8, on fuse 2.34 the reading was 11.67. Let me know next steps.

Thanks again for your assistance!!!

 

[wmburns]

and PATS was keeping the fuel pump from coming on.

A couple of things here. Ford factory PATS does NOT disable the power to the fuel pump. Instead it works by withholding fuel injector pulse. So if there's no power to the fuel pump it is NOT a PATS related problem but instead something else.

I have a pin out diagram and pin 55 (reference voltage supplied at all times - overload protected) and pin 90 (reference voltage) are not showing anything on the volt meter, with the key on at the 2nd position or with the key removed. When I turn the key to the 2nd position the fans come on and I hear relays clicking, but no voltage at the connector.

The fact that there is confirmed key on power to fuse F2.34, F2.2 and F2.8 "proves" that:

• The ignition key on pilot duty circuit is working.
• that the CCRM is working and supplying power to the down stream devices.
• That the "always on" fuses inside the battery junction box that supply these circuits are not blown.

Next we need to CONFIRM there is key on power at the trunk mounted IFS switch.

Then CONFIRM there is power to the motor's VPWR ignition circuit by testing for key on power at one (or more) COP's.

So this also tells me that there's an external wiring harness problem that accounts for the no key on voltage at PCM pin 55 and 90 (assuming that all of the other fuses have been visually inspected).

So let's start with PCM pin #55. This is supplied via fuse F2.21. We need to confirm "always on" power in and out of fuse F2.21. If there is, and there's no power at PCM pin #55 there HAS to be a wiring fault between the CJB and the PCM. My diagrams indicate there is a splice and a connector this circuit passes through.

 

[tsgman01]

I have a question regarding the fuel pump. There is power at the fuel pump connector (close to 12v) but I do not hear the fuel pump "prime", I am not sure if that's the same thing you referred to above when you stated PATS does NOT disable power to the fuel pump.

As far as the IFS switch, should the power be there only when the key is turned? (Will there be power there with no computer connected?) I did not test this yet.

I have no clue what a COP is?? (google doesn't either, lol)..

For fuse F2.21, when you say "in and out" what are you referring to? I tested voltage there, the red wire with the white stripe had no voltage with the key on or off. The caramel colored wire had a reading of 11.80v with both the key off and key on.

PCM pin 55 had no voltage with the key on or off

PCM pin 90 had a voltage of 1.67 with the key on, no voltage with the key off.

Again, thank you for your assistance (and patience)...

 

[wmburns]

I have a question regarding the fuel pump. There is power at the fuel pump connector (close to 12v) but I do not hear the fuel pump "prime", I am not sure if that's the same thing you referred to above when you stated PATS does NOT disable power to the fuel pump.

As far as the IFS switch, should the power be there only when the key is turned? (Will there be power there with no computer connected?) I did not test this yet

The fact that there's power at the trunk mounted IFS switch "proves" F2.34 and the CCRM.

I'm going out on a limb here. The fact there's no fuel pump prime likely means that the PCM isn't working enough to command the fuel pump to prime.

I have no clue what a COP is?? (google doesn't either, lol)..

COP=Coil on Plug. The ignition coil things on top of each spark plug used for the 1999-2004 model years (and later).

For fuse F2.21, when you say "in and out" what are you referring to? I tested voltage there, the red wire with the white stripe had no voltage with the key on or off. The caramel colored wire had a reading of 11.80v with both the key off and key on.

Every fuse has two sides. Supply (Input) and load. Testing both sides means to confirm power on the input and load side of the fuse. Most fuses have a small metal piece that stick above the plastic that makes it easy to "probe" and test for power. OBTW, a blown fuse would have power on the input side but not on the load side.

Soooooooooo If no power into fuse F2.21 would explain why there's no power at PCM #55.

We need to know if there's "always on" power in and out of fuse F2.15 as well as the BJB fuse F1.6 to the TN/BK wire. Again test for power in and out of the fuse.

Again best to use a test light that will "load" the circuit. You did "test" all of the fuses right (or at least visually inspect them)? The exact test results will "focus" where to look for the blown fuse, bad connection, or wiring fault.

 

[tsgman01]

ok, long week.... just to make sure I am doing this correctly, the F2.15 fuse has ~12.5 volts on the purple/blue wire and not the red/black wire. the test light (pic below) that I am using lights up on the same wire with the volts and does not on the side with no volts. So does that mean that the out side of the fuse is bad?? (refering to the power in and out you referenced above). Fuse 1.6 has ~12.7 volts on both sides using the probe on the metal pieces that is on top of the fuse.

I visually inspected all fuses when I installed the wire harness in the car and they were all good.

Thanks!!!

 

[wmburns]

I have several working theories.

• there are differences in the wiring harness between the 2003 and 2004 model year
• there is a problem at SPLICE S260 which feeds the TN/BK wire
• There is "an issue" inside the CJB such that not all of the fuses on the same supply buss are being powered.
• There is a wiring FAULT between the BJB and CJB

Test for "always on" power (with the key OFF) at the following fuses. When replying keep the list in order. Use the test light to "load" the circuit. I'm thinking that the combination of exactly which fuses have power (or not) will narrow down where the problem is.

For this test REMOVE the fuses and test for power on the supply side. Do not test on the load side as this will give a false positive.

F2.1 F2.7 F2.13 F2.19 F2.25 F2.31
F2.15 F2.21 F2.27 F2.9 F2.33 F2.39

Note, IF the problem is a bad splice S260 THEN one of the groups above will have power and the other not.

If this is a problem caused by a difference in the wiring harness it will be necessary to compare the connector pin out between the different model years. If interested in getting a model year specific set of Ford factory wiring harness diagrams I may be able to help. PM if interested.

If this were my car I would likely pull the CJB and perform a through visual inspection looking for heat damage, bent/pushed pins, broken wires, or corrosion.

It also might be interesting to power fuse F2.21 from an external fused source or jumper wire. One method to do this is with an "add a fuse" or "add a circuit". For this test IMO it's vital to use a fused source as fire is a possibility. Sometimes the test light itself is able to supply enough power to make a small amp circuit wake up. Put the test light pig tail on battery positive and probe fuse F2.21 with the key on.

What might this test prove? IF the problem is the "always on" circuits going to the PCM then it's possible that the PCM will "wake up" and start talking. One clue that the PCM is alive is if the cluster no longer displays all dashes and the cooling fan doesn't run at initial key on.

Note PCM pin #90 is a VREF supply that comes FROM the PCM. So the fact that PCM pin 90 doesn't test for power confirms that the PCM isn't alive. I really feel that once PCM pin #55 has the correct "always on" power that it's likely the PCM will work.

 

[tsgman01]

Ok, i did not test F2.21 from the battery, I don't have any wire lying around, will get some tomorrow.

With the fuses removed:
For the group below, F2.2 had no volts/light, the rest had ~12.5 volts/light. The volts/light was read using the left side of the fuse when looking at the fuse side of the CJB, the right side of every fuse produced no volts/light which is what was expected??.
F2.2 F2.7 F2.13 F2.19 F2.25 F2.31

For the group below they all had ~12.5 volts/light using the left side of the fuse when looking at the fuse side of the CJB, the right side of every fuse produced no volts/light which is what was expected?
F2.15 F2.21 F2.27 F2.9 F2.33 F2.39

Being that the dash is not in, I have a very good view of the CJB, all wires look good, no splices, no torn/cracked wires, no corrosion and the electrical tape around them leading up the CJB is in good condition.

Thanks again!!!

 

[wmburns]

For an "always on" circuit with the fuse pulled one should expect there to be power at the supply terminal and nothing on the load terminal. So unless I don't understand your prior post, then there is always on supply power available at fuse F2.21.

Since there's power into (supply) fuse F2.21 but no power at PCM pin #55, we should focus on the wire path from the CJB to the PCM. There has to be a break down between these two points.

So with power into fuse F2.21 anyway it won't do any good to power fuse F2.21 from an external source.

Just to make TRIPLE sure that the fuse itself is good. Further to make sure that the fuse is actually inserted into both blades of the female fuse holder. I remember helping someone where the problem turned out to be a fuse blade on the outside of the female blade holder.

The RD/WH wire of fuse F2.21 passes through connector C215 pin #16. If this were my car, I would confirm "always on" power at that connector. Either back probe both sides of the connector. If this is not possible then open the connector and visually inspect for bent/pushed pins. What we are trying to do is figure out where the circuit is breaking down. IE before or after the connector. That sets the direction where to focus next.

If this were me doing the work I would verify that power at C215 pin #16 does in fact come and go with the removal and insertion of fuse F2.21. This offers a way to double confirm that the correct wires are in fact being isolated.

Could also be useful to "ring out" the wire path from connector C215 to the PCM. As well as from C215 back to the CJB. Again I prefer to use a test light to that applies a small load to the circuit.

 

[tsgman01]

I will test the connector/pins and trace the wires. But I need a description of C215 and where its located, thanks!

 

[wmburns]

If interested in getting a full copy of the Ford service manual and wiring diagrams I maybe able to help. PM if interested.

Or try www.alldatadiy.com