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Ask A. Penland Your Own Question
A. Penland
A. Penland, Ford Senior Master Technician, ASE
Category: Ford
Satisfied Customers: 6577
Experience:  ASE Master Certified, ASE Advanced Gasoline Engine Performance
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2000 Expedition 4.6L, replaced failed pcm with used pcm.

Customer Question

2000 Expedition 4.6L, replaced failed pcm with used pcm. Part numbers match, both end in DF. Using Autel Maxidas scan tool, reset PATS parameters then recoded both keys. Now engine cranks but won't start, theft light flashes. No communication to pcm with scan tool. U1262 code permanent dtc.
Submitted: 1 year ago.
Category: Ford
Expert:  A. Penland replied 1 year ago.
Hello and thanks for using JustAnswer.I will try my best to help you with your question.
What was the original problem with the original PCM?
I need more information on why you replaced the PCM?
Customer: replied 1 year ago.
First mechanic to look at it pulled out the pcm and said it was bad, then he disappeared so the customer called me to take a look at it. With the old pcm, it would crank but not start. Theft light not on. Only code was u1262, communication failure between instrument cluster and pcm. Followed diag flow chart, found good power and grounds at pcm, chart advised replace pcm
Expert:  A. Penland replied 1 year ago.
It is not a power or ground issue. The problem is the communication network between the DLC and the PCM connector. This is the communication network for the vehicle.
You will have to disconnect the CM and check continuity between the DCL connector pin #2 and PCM connector pin #16
then DLC pin # ***** and PCM pin #15.
Customer: replied 1 year ago.
Good continuity on the wires you listed
Expert:  A. Penland replied 1 year ago.
What module did the U1262 come from? The PCM or the Instrument cluster?
Customer: replied 1 year ago.
PCM and cluster both had that code. I put the old pcm back in today and now it won't communicate
Expert:  A. Penland replied 1 year ago.

We need to check the communication wiring between the cluster and the PCM. Below are the wiring connector pin out charts for both. Check the continuity between the cluster pin #1 Tan/Orange wire and the PCM connector pin #16 Tan/Orange wire. Then check the continuity between cluster pin #2 Pink/Light Blue wire and the PCM pin #15 Pink/Light blue wire.

Customer: replied 1 year ago.
Found good continuity on both those wires
Expert:  A. Penland replied 1 year ago.
Is this PCM used, new or remanufactured?
Customer: replied 1 year ago.
It's used. Additional info, checked for VREF at TPS, shows only .6 volts with either pcm. Power present at pcm relay, relay bench tested ok. I took some screen shots of the live data from the HEC if that helps.
Expert:  A. Penland replied 1 year ago.

VREF should be 5 volts at the sensors. Ford uses 5 volts for reference.

Customer: replied 1 year ago.
I know it should be 5 volts, what I'm saying is theres no 5 volt reference present at the TPS with the ignition on. This is on the brown/white wire with the sensor disconnected. So that means the pcm is not sending out a reference voltage, so it's not just a communication lbus issue
Expert:  A. Penland replied 1 year ago.

Check these fuses below.

In the dash fuse box, fuses #2 and #30

In the engine bay fuse box, fuses #2 and #18