2010 F250 6.4L no crank no start condition

Good day to the group , my first interaction with vehicle was to program a spare key which was done successfully. Got a call back a few days later stating the truck would not start and the immobilizer light was flashing in the cluster. Thinking maybe I had a bad key returned to correct that issue but in pluging in my programmer I would get to learning the key and it would fail. On retry , I noticed that the cluster would go black when entering the programming stage So a diagnostic scan was performed to see the codes and there was the beginning of this drama no communication with my Ecm /Tcm or nothing on the High speed can network. Using the Verus D10 scope , the High speed Network ohmed at 112 ohm so a resistor was missing. Next step verified power and ground to PCM all checked out fine but then the weird stuff started .1- If the connector c1232 is removed the PCM the voltage disappears from fuse # 72- pin 1,3 and 5
2- Connector 140 was disconnected to isolate the rest of the HS network leaving the PCM in circuit still no communication
If the scope is correct, where is that reading coming from if the PCM is faulty? Also there are some small spikes going in same direction and not opposite
I want to call the PCM but needed a second opinion

Hey fahead32! I wanted to clarify a couple things:

Using the Verus D10 scope , the High speed Network ohmed at 112 ohm so a resistor was missing.

Where were you taking this measurement? At the DLC? Which pins were you probing, exactly?

1- If the connector c1232 is removed the PCM the voltage disappears from fuse # 72- pin 1,3 and 5

You mean C1232B, correct? That makes sense, since it's the PCM that grounds the PCM Power Relay at pin 33 of C1232B. Without that ground, the PCM Power Relay won't close, and you'll lose power to fuse #68, 72 and 76:

2- Connector 140 was disconnected to isolate the rest of the HS network leaving the PCM in circuit still no communication

I (badly) smashed the two network pages together for reference:



By my reading of the diagram, disconnecting C140 would have isolated the turbocharger actuator and the PCM from the DLC. :huh: I may not be understanding your test correctly.

If you measured 120 ohms between pins 6 and 14 of the DLC, then I'd suggest using C140 as a convenient way to break the circuit in two for testing purposes. Ohm the network in both directions to see where your open is. Or, stay connected at 6/14 and unplug C140. If the resistance stays at 120 ohms, your open is towards the PCM. If it goes infinite, your open is towards the Instrument Cluster.

Thanks for the reply,
Yes the dlc was my measuring point , also the reading remained when c140 was disconnected so would the PCM HS network need to be terminated to rule out PCM

fahead32 wrote:

Yes the dlc was my measuring point

At pins 6/14? Sorry to harp on this, but it matters.

also the reading remained when c140 was disconnected so would the PCM HS network need to be terminated to rule out PCM

If you have a 120 ohm resistor available, you could connect it across pins 34 and 47 at C1232B to see if your resistance reading goes to 60 ohms and you get HS-CAN communication back. Or, disconnect C1232B and ohm across pins 34 and 47. Should measure 120 ohms.

Use a break out box so I would have a conveinent spot have scanner wireless vci and can check pin 6 and 14

fahead32 wrote:

Use a break out box so I would have a conveinent spot have scanner wireless vci and can check pin 6 and 14

Gotcha, thank you.

Any luck with this one?

Will return to vehicle Tuesday

Just read what you said carefully my problem seem to be with PCM then. Quick question, do the PCM have both or only one terminating resistor? Still at the vehicle as you can guess

fahead32 wrote:

Just read what you said carefully my problem seem to be with PCM then.

If you disconnect C1232B at the PCM and measure resistance across 34 and 47 on the PCM side, does it measure 120 ohms?

Quick question, do the PCM have both or only one terminating resistor? Still at the vehicle as you can guess

Only one. The other is in the Instrument Cluster.

Quick update on the vehicle , the problem was solved after bringing a technician who is more experience than me to look at the truck . The problem turned out to be that the harness bulk connector was closed but not completely seated . All said the normal precedure of looking not moving wiring because you may fix the problem unexpectedly was the fix in this case. He said for no communication issue that is where he checks first.
After swallowing hard , I posted this to say nothing beats experience and you have to learn to check everything no matter how secure it looks
Thanks for all the help everyone

We appreciate the update. Thank you.