PCM Will Not Power Down

Ken Diagnostician Fortuna, California Posted   Latest  
Resolved
Driveability
2005 Ford F-150 Lariat 5.4L (5) 4-spd (4R75E)
Pcm Stays Awake

Need some help, with key out of ignition and on the dash I still have data with scan tool (VCM2). The scan tool will display data until the battery goes dead. What is the PCM looking for to power down or go to sleep? Checked all VPWR circuits off of ignition switch all correct in off, key on, and crank position. Removed fuse 34 no change. Load tested all ground to PCM ok. Load tested KAPWR, and V4WD circuits ok. Intermittently the vehicle is a no crank condition and will drain battery in a short period of time. I can get it to act up very consistent now. There is a B1681 DTC PATS transceiver module signal is not received. Notice the sercurity led on dash does not blink at times, or flashes faster than normal. The transceiver module is sending signal to PCM.

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Allan Owner
Sterling, Virginia
Allan Default
   

Smack the top of the dash over the cluster and see if that works. The retained accessory power is in the cluster I think. If that’s no help. Swap the pcm power relay with a similar one

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Ken Diagnostician
Fortuna, California
Ken Default
 

I did disconnect cluster with no change, also swapped pcm power relay no change i believe fuse 34 pulled eliminates that also.

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Chris Technical Support Specialist
Commack, New York
Chris Default
 

You might try also removing the always powered fuses, F5,F29,F30 to see if you can get it to fully power down. Most of the newer Fords will not sleep without seeing Park signal but I think this is a little old for that function.

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Ken Diagnostician
Fortuna, California
Ken Default
 

Chris, F5, F29, F30 are hot all the time correct? The park signal I will go check. There was 2 pids one indicated Park the other stated Neutral I believe. I did disconnect the cluster with no change

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Scott Technician
Chico, California
Scott Default
 

I just got done with an 06 Ford that had this kind of issue. The pcm sees park from the range switch on the trans. But the cluster might be looking at the physical shift lever for a park signal. Look at pcm indicated gear and ipc gear. Just my 2 cents

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Carl Technician
Baytown, Texas
Carl Default
 

hi chris, i think me spoke today on the phone...Someone from Opus called me anyway, and sure enough i needed to bounce a question off of someone 5 minutes later..

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Michael Owner/Technician
Cartersville, Georgia
Michael Default
 

Hi Ken, If you thought that the PCM would not go to sleep because of something on the network then disconnect the PCM and do a parasitic draw test. If there's a draw then do your normal testing to see what's not sleeping and sending data on the network. If there's no draw then you can focus on inputs to the PCM. Good luck, Mike

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Geoff Diagnostician
Lahaina, Hawaii
Geoff Default
   

Check for water intrusion in PCM connectors and inside PCM. IC and ABS are on the same network as PCM so disconnect those to see if PCM stops staying awake.

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Walter Mobile Technician
Plantation, Florida
Walter Default
 

Check the relays and the diodes in the relay and fuse boxes. If my memory serves me correctly there is a relay/diode that fails causing this issue. Possibly someone replaced a diode with a fuse.

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Walter Mobile Technician
Plantation, Florida
Walter Default
 

Check the AC Clutch Relay which is possibly back feeding 12V to F32 and PCM Power Relay.

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Reid Owner/Technician
Beachwood, New Jersey
Reid Default
 

I ran into this same issue on a similar F150. I can’t remember all the details but in my case there was one fuse that remained powered in the junction block in the right kick panel. It was related to the PCM power relay circuit. While the fuse didn’t show full battery voltage after vehicle shutdown it did flow enough current to allow the PCM relay to remain energized. The root cause was current…

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Mohammadu Diagnostician
Auckland, New Zealand
Mohammadu Default
 

Ken Rocha Try to remove fuses one by one and trace that wire where all connected​.​Few circuits may oparate from same power so check it carefully. I have solved few problems like that but not in the fords​.​If the PCM is not allowing to power down disconnect the PCM and see what happens.I guess the someone may wires up for a accessory relay that might cause the problem.

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Ken Diagnostician
Fortuna, California
Ken Resolution
 

Thank you for the suggestions, fuse 34 when removed had 12 volts on one terminal and 18 volts on the other. We got detoured by not pulling up power distribution diagrams for fuse 34. The A/C relay was internally shorted between the switch side and control side. This was causing fuse 32 to back feed to fuse 34, 33 etc (switch side of relay hot at all times) I wish I would have took Walter…

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