factory keyless entry
01-23-2016, 04:42 PM
#1
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factory keyless entry
hi all, ive read multiple topics about the keyless entry key pad biting the dust but this doesnt seem to be the issue for me.
about a week ago i noticed my keypad no longer did anythingon my 2008 f150, in the 2 years ive owned the truck its never lit up so i assumed it was just dead. last weekend i pulled apart the door and keypad, cleaned all contacts and got any dirt and grime out of the circuit bored to no avail. today i installed a new key pad and still no luck. checking for power at the plug i get nothing and my understanding of the wiring diagram is that the keypad is hot at all times and what completes the circuit is when each button is pushed and is ground through the same ground as the window regulator, after checking all related fuses and wiring in the door jams im starting to think my VSM his onits way out? im hesitant about thinking that only because this started happening right after a PCM update/reprogram was being done and the IDS crashed leaving me to reprogram with an as-built status, could that have anything to do with the issue im facing?
about a week ago i noticed my keypad no longer did anythingon my 2008 f150, in the 2 years ive owned the truck its never lit up so i assumed it was just dead. last weekend i pulled apart the door and keypad, cleaned all contacts and got any dirt and grime out of the circuit bored to no avail. today i installed a new key pad and still no luck. checking for power at the plug i get nothing and my understanding of the wiring diagram is that the keypad is hot at all times and what completes the circuit is when each button is pushed and is ground through the same ground as the window regulator, after checking all related fuses and wiring in the door jams im starting to think my VSM his onits way out? im hesitant about thinking that only because this started happening right after a PCM update/reprogram was being done and the IDS crashed leaving me to reprogram with an as-built status, could that have anything to do with the issue im facing?
02-24-2016, 11:27 AM
#3
02-24-2016, 11:34 AM
#4
TOTM 8/2019
You are correct, the VCM supplies +5VDC to EACH of the keypad buttons via a discrete line. When you push a button, it shorts that +5VDC to ground, and thus the VCM knows you pushed it (the VCM has an internal pullup resistor so it can be shorted to ground without burning anything up).
That being said, you NEED to have the +5VDC at the buttons for this to work. Since you stated it is NOT there, what I would do is go to the VCM, and use a meter to measure if there is voltage at the source. You could have 2 issues here:
1)The VCM is fine, but the wires that run between the VCM and keypad are damaged and are shorted to ground, therefore the VCM will see ground at all times (most likely)
2)Your VCM is actually broken.
It is easy to determine which scenario, just UNPLUG the connector on the VCM that has the wires to the keypad(this will isolate if there is a short in the wires to the keypad. Measure for voltage now at the VCM, if you have +5VDC at this point, then you have a short in your wiring somewhere. If you still have GND or 0VDC(or something less than 3VDC), you could have a VCM issue.
Brian
That being said, you NEED to have the +5VDC at the buttons for this to work. Since you stated it is NOT there, what I would do is go to the VCM, and use a meter to measure if there is voltage at the source. You could have 2 issues here:
1)The VCM is fine, but the wires that run between the VCM and keypad are damaged and are shorted to ground, therefore the VCM will see ground at all times (most likely)
2)Your VCM is actually broken.
It is easy to determine which scenario, just UNPLUG the connector on the VCM that has the wires to the keypad(this will isolate if there is a short in the wires to the keypad. Measure for voltage now at the VCM, if you have +5VDC at this point, then you have a short in your wiring somewhere. If you still have GND or 0VDC(or something less than 3VDC), you could have a VCM issue.
Brian