[spike817]

An update.

Replaced the ignition switch. Ignition switch circuits now function correctly in the run/start positions but I now have funky instrument cluster behaviour.

The rabbit hole gets deeper and I am certainly not confident in the cab wiring. I feel I'm missing something major here — probably some chafe in a major harness. But like Hydro says... Without proving the rest of the system is good... Banking on a faulty PCM is a gamble.

Gonna need some more time on this truck — a lot more time. I'll have to leave this forum on hold until I find more time to figure it out.

If I end up finding the cause I will absolutely post my findings.

Just wanted to say thanks for your time and patience for helping me out guys; I appreciate it.

 

[spike817]

@bismic @Hydro



Hey guys, Its been a while but I am back with the truck again finally to try and figure this out.



Bismic, I've went through your guide once more just to see where I'm at and if anything has changed. Now, something has changed and I was wondering if you and Hydro could elaborate on what it means. From your guide bismic:

Check resistance between pins 6 (CAN PLUS) and 14 (CAN MINUS) on the DLC with the key off. Should be 0, 60, or 120 ohms. Everything is OK if it is 60 ohms.

Pins 6 and 14 are the CAN bus (+) and (-). Pin 6 is the CAN serial data highway line.
Diagnostic data is communicated through the CAN to the diagnostic tool. The CAN network is used for HEC (Instrument Cluster), ABS, and TBC communications.
The CAN bus runs at split voltage.
Check voltage relative to ground at pin 6 and then at pin 14 with the key off.

Check voltage relative to ground at pin 6 and then at pin 14 with the key on.

Each time, the voltages at Pin 6 and Pin 14 should add up to apprx. 5 volts, with CAN PLUS being slightly higher than CAN MINUS. CAN PLUS voltage will increase with increasing network activity.

Firstly, checking resistance between pins 6 and 14 of the DLC connector (the CAN Plus and CAN Minus) with the key off... I read 121.6 Ohms. I garner that this means that one of the terminating resistors in either the HEC or the PCM is gone. However, I have managed to get a hold of both a brand new HEC and a spare PCM to test on and upon swapping out their respective replacements one-at-a-time or both at the same time, I still read 120 ohms in all cases and I am not sure what to make of that.



I will add that I have tested for a short or open circuit along the CAN PLUS and CAN MINUS lines between the PCM and the DLC, to possibly rule out a short or broken line between the two.

Probing pin 6 of the DLC and pin 13 of the PCM connector C1381a, as well as pin 14 of the DLC and pin 14 of the PCM connector C1381a, yielded ~1 ohm for both. So, I am reasonably confident that there isn't a bad wire on the CAN Bus between the PCM and the DLC.


Secondly, checking the split voltage on the CAN Bus via pins 6 and 14 on the DLC yields 0V in every case. That is, 0V for key off CAN PLUS to ground, 0V for key off CAN MINUS to ground, 0V for key on CAN PLUS to ground and 0V for key on CAN MINUS to ground.



Now, I'm not entirely certain how the split voltage works or where it comes from exactly so I'm not sure where to go from here. Hydro/Bismic, I'd be interested to know if the lack of split voltage entirely tells you something or if it prompts some more tests to conduct.



Thoughts?

 

[Hydro]

Measure the ohms on the data lines with the pcm and inst disconnected
would be looking for a zero reading here

it has been suggested that one of the terminators is in the abs module
the literature is unclear of their locations
possible changed by different year models
I do not have hard info on that

The data lines should have voltage with the key on -- this adds up to 5 ish volts
and is usually 2.4 and 2.6 for hi and low
tho the individual voltages may be some different , depending on buss traffic

 

[spike817]

Measure the ohms on the data lines with the pcm and inst disconnected

would be looking for a zero reading here



it has been suggested that one of the terminators is in the abs module

the literature is unclear of their locations

possible changed by different year models

I do not have hard info on that



The data lines should have voltage with the key on -- this adds up to 5 ish volts

and is usually 2.4 and 2.6 for hi and low

tho the individual voltages may be some different , depending on buss traffic

With the PCM and INST disconnected, measuring across the data lines (i.e., probing pins 6 and 14 of the DLC), I am indeed getting a zero/open reading.



I can confirm with the keys on, the data lines both read 0V for sure. What do you reckon the cause of this is? Anything you'd like me to test out?

 

[bismic]

I would unplug the ABS and the TBC and re-test the voltages at #6 and #14. You might need a bit of WD40 on the ABS connector.

 

[Hydro]

pcm and inst , one a time
do you get 120 ohms ?

on the data line voltage
do you get wait to start light when you key on ?

yuppers , about all WD40 is good for is lubrication and washing out electrical connectors -- at that job is works well

 

[bismic]

pcm and inst , one a time
do you get 120 ohms ?

on the data line voltage
do you get wait to start light when you key on ?

yuppers , about all WD40 is good for is lubrication and washing out electrical connectors -- at that job is works well

WD40 is good for yellow jackets in deer blinds also!

 

[Hydro]

Brake cleaner and a lighter

 

[spike817]

pcm and inst , one a time
do you get 120 ohms ?

on the data line voltage
do you get wait to start light when you key on ?

yuppers , about all WD40 is good for is lubrication and washing out electrical connectors -- at that job is works well

Pcm connected: 121.2 Ohms.
INST connected: Open Circuit.

Both the brand new and old INST both yield an open circuit.

I take it the INST terminating resistor is the one not acting on the circuit? Since it also happens for the new INST, you reckon a break/short/bad pin along those data lines on the INST side?

No 'wait to start' on this year I believe. Has glow plug symbol instead and it indeed comes on

 

[spike817]

I would unplug the ABS and the TBC and re-test the voltages at #6 and #14. You might need a bit of WD40 on the ABS connector.

ABS and TBC disconnected: Still 0V on both pins and with key on/off.

 

[spike817]

Brake cleaner and a lighter

Don't tempt me haha

 

[Hydro]

So ,with none of the controllers connected the ohms should read open (zero)
The pcm and instrument should have the terminator resistor in them

So, connecting the instrument panel should give 120 ohms
-- same for connecting the pcm

with both connected the ohms should read 60

The terminators are at the ends of the can buss , to dampen the noise in the buss
the system will work with just one terminator , but will usually throw random codes

This is confusing to me :

"
Pcm disconnected: 121.2 Ohms. -- what was connected here to get the 120 ?
INST disconnected: 0 or Open Circuit. -- pcm connected ?
Both the brand new and old INST both yield an open circuit" -- connected alone you get no ohms reading ?

Testing ohms is to be done with the key off

Looking at the 2003 and 2005 diagram , I see that the odb port was in a different spot in the circuit

 

[spike817]

So ,with none of the controllers connected the ohms should read open (zero)
The pcm and instrument should have the terminator resistor in them

So, connecting the instrument panel should give 120 ohms
-- same for connecting the pcm

with both connected the ohms should read 60

The terminators are at the ends of the can buss , to dampen the noise in the buss
the system will work with just one terminator , but will usually throw random codes

This is confusing to me :

"
Pcm disconnected: 121.2 Ohms. -- what was connected here to get the 120 ?
INST disconnected: 0 or Open Circuit. -- pcm connected ?
Both the brand new and old INST both yield an open circuit" -- connected alone you get no ohms reading ?

Testing ohms is to be done with the key off

Looking at the 2003 and 2005 diagram , I see that the odb post was in a different spot in the circuit

Sorry Hydro, that was a typo on my part. I said disconnected when I meant connected.

Correcting myself...

• With neither the PCM or INST connected: the resistance across the CAN bus lines is 'open'.
• With only the PCM connected: the resistance across the bus lines is 121.2 ohms.
• With only the INST connected, the resistance across the bus lines is 'open'. This remains true when tested with either the new and old INST.

This was all done with the key off.

 

[MtnTallPaul]

"Pcm disconnected: 121.2 Ohms. -- what was connected here to get the 120 ?"

Something else on the CAN bus. Can't tell you what.

There should be two 120 ohm terminations on the bus. If they are both present on the bus, you would see 60 ohms across the bus.

 

[spike817]

"Pcm disconnected: 121.2 Ohms. -- what was connected here to get the 120 ?"

Something else on the CAN bus. Can't tell you what.

There should be two 120 ohm terminations on the bus. If they are both present on the bus, you would see 60 ohms across the bus.

Yeah sorry that was a typo on my part earlier.
I said PCM disconnected when I meant PCM connected.

When the INST was disconnected and the PCM was connected... The resistance across the bus lines was 121.2 ohms. I.e., the PCM terminating resistor is active in the circuit.

Its the other resistor in the instrument cluster that's not active — provided that's where the other resistor is. Hydro had mentioned not being certain on it being in the INST for all years.

 

[MtnTallPaul]

You might want to contact Circuit Board Medics and discuss the issue with them.

 

[Hydro]

Here is a decent vid on the basics of CAN Buss testing and how it works
the vid is on a BMW , but the buss operation will be the same

 

[spike817]

Here is a decent vid on the basics of CAN Buss testing and how it works
the vid is on a BMW , but the buss operation will be the same

Thanks Hydro. I'll look into this tomorrow.

 

[bismic]

An interesting read in this thread (just to perhaps get people to think about things a bit differently).

Electronic Issue? Multiple Codes, CAN Bus Issues, Instrument Cluster? - Ford Truck Enthusiasts Forums

6.0L Power Stroke Diesel - Electronic Issue? Multiple Codes, CAN Bus Issues, Instrument Cluster? - It has been a while since I posted this, and I have some new information, so this original post is being updated on 5/7/2014, at noon. 2006 F-250 Lariat FX4 4x4, 6.0L, 5R110, 45K miles. Truck...

www.ford-trucks.com

 

[bismic]

I am wondering if you have a short to ground in the wiring to the Instrument Cluster or in the instrument Cluster connector.