I have 12 volts (there should be none) at the VT (violet wire) at the data link connector below the dash. I removed the electrical connector from the instrument cluster and the voltage went away. Any ideas as to what is shorted in the IC?

 

The VT wire doesn't go the cluster, it goes to the PCM. It's the FEPS line and is supposed to be powered by the scan tool at 18V during programming operation. What it reads other than that probably isn't relevant.

 

Which violet wire are you talking about, there are 2 in the connector.

One goes to the FEPS output ( ckt 107 ) on the PCM the other is the UBP communications network ( ckt 1906 ) both are side by side, so it is easy to short the 2 together if you do not have fine point meter probes.

The UBP comm network has a connection to the instrument cluster, but it is also to the VSM / BSM, the drivers seat module and the EATC ( if equiped ) as well ( communications network between the devices that need to communicate ).
All the devices need to be operating for the UBP comm network to function ( if one has a problem, they all do ).

If you were probing for the UBP and shorted the output of the PCM to it, that could cause serious issues.

 

2004 F150 FX4 5.4L Auto. No seat memory. Manual air conditioning.


Code received: U1950 (Instrument Cluster):
Test: Pinpoint Test K: No UART based protocol (UBP) Network Communication

Test Step K3: Measure the resistance between the DLC C251-3, circuit 1906 (VT), harness side and ground. The resistance should be greater than 10,000 ohms. RESULT: I have no resistance at all.

Test Step K4: Key on. Measure the voltage between C251-3, circuit 1906 (VT), harness side and ground. No voltage should be present. RESULT: I have 11.5 volts.

I removed the instrument cluster connectors and the voltage went away on C251-3.

 

If you want assistance, you probably ought to back up and start from the beginning...

You might already be off in the weeds...

 

You may be correct about being off in the weeds. So here it goes.....

1. Transmission fails for the same reason all of them fail…the servo clip broke and I lost overdrive
2. I run codes. Retrieved are: 4X4 Control Module: B1318 and U2023; Antilock Brake: C1230; Instrument Cluster: B1352 and U1950; Parking Aid Module: B2373 and C1704. No transmission codes.
3. Take the truck in to dealership for warranty repair of transmission. I ask them to take their time as I consider transmission work rocket science. And since it’s there, take a look at the codes mentioned in step 2 above.
4. I get the truck back and the only thing addressed was the transmission problem mentioned in step 1.
5. On my way home the transmission stumbles on a downshift from 2nd to 1st.
6. Arriving home, I repeat step two above with the same results.
7. I park the truck until I can address the codes in step two, figuring if the transmission problem can be blamed on something else then I want those issues addressed.
8. I begin with U1950. I find tests K3 and K4 fail. I begin disassembly of the interior, following the 1906 (VT) wire to the body control module.
9. I discover water is being retained in the rocker panel on the driver’s side.
10. Seal hairline cracks in high mount third brake light.
11. Begin cleanup. No wonder there’s no resistance I say to myself. Water.
12. Everything dry (except maybe the space between the wires and their jackets)
13. The body control module tests fine via Fluke multimeter
14. Move to instrument panel. Find when instrument panel is plugged in, I get 11 volts and zero ohms at the number 3 pin on the data link connector. When it’s not plugged in no voltage to the number 3 pin on the data link connector.

 

I forgot to add 'lots of cursing and throwing a hissy fit getting the back seat out of this super cab'.

 

and these two sweet gems fell out as i was removing various connectors from the steering column.

http://i1175.photobucket.com/albums/...ps09c4a585.jpg

 

When you post "The body control module tests fine via Fluke multimeter" you have less than 5 ohms of resistance from the BSM to the instrument cluster ?
- Keep in min the entire circuit cannot have more than 5 ohms of resistance on it. Need to verify that when you short the meter probes you have 0 ohms of resistance on them before you start testing.
No resistance is the desired results.

Did you check the DSM to circuit 1906 splice ?
- If you had water being held in the door sill I would suspect that the splice has an issue by now and you have not found it.

 

Thanks SSCULLY, here is the result of the ohm reading from the BCM to IC. The truck does not have memory seats, so there is no 1906 (VT) wire going to to the DSM, nor a splice (correct me if I'm wrong).

 

that is correct, no memory seats, no DSM.

2004 FX4 the LUX was not out, so unless you changed it yourself, the HVAC is ETMC ( manual ).

Just took a look at pinpoint test K, the check for + VDSC is to be done with all items ( BSM & instrument panel ) unplugged ( step K2 ).
You are not performing test K4 correctly ( skipped a test ).
- Short to ground and Short to voltage are for checking the Violet wire ( ckt 1906 ) to ground or + VDC on its own, not when plugged in.

Did you check the front of the connector to the BSM for damage ( usually only happens with autolamps ).

Did you check the ground to the BSM on the back wall of the truck ?
- Few have noted a loose ground lug at times, think it is mostly a 2005 occurrence.

 

OK. I had to walk away for a while to clear my head. I've put the truck back together and cleared all codes. I'm starting over fresh.

 

Apparantly the issue was the water being in the rocker panel and the wiring harness taking a bath. After the wires were dried out, I put the truck back together, cleared codes and went for a drive. All codes gone.

I also cleaned the throttle body (with the proper cleaner) and replaced the 3/8" vacuum line that runs from the RH side of the motor to the vacuum tree adjacent to the brake booster. Truck ran like a scalded cat for 20 miles. Next day it stumbles upon acceleration and backfired once. What did I do now?

No new codes. I'm going for a drive with my computer to see if I can narrow it down.

 

How did the water get into the rocker panel. (I know how it probably did, I'm just seeing if you know how). They didn't build the truck with it, and it will get in there again and cause the same problem. Gotta fix it and eliminate that problem. (meaning water source AND wire corrosion)

 

no new codes, but are all the same old codes there ?

The back fire, and changing the vac line to the brake booster from the back of the intake, did the recall vac line come undone ( or did you even have the recall done ) ?