PCM wiring diagram needed - Ranger-Forums - The Ultimate Ford Ranger Resource


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  #1  
Old 07-28-2008
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PCM wiring diagram needed

I am in the need of the wiring diagram for the PCM which shows which pin or color wire goes to what. My coil is not getting enough voltage to lock it in and I am in need to see which wire come out of the PCM towards the relay or coil to make it lock in. This is a 2005 Ford Ranger Edge 2wd with a 3.0
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Old 07-29-2008
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Can you explain "lock it in"? Have you measured the 12V at the coilpack (red/lt. green wire)? Measure this voltage WRT GND, ignition switch in the RUN position.

Last edited by Takeda; 07-29-2008 at 06:11 AM.
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Old 07-29-2008
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Sorry wrong coil. I mean the coil on the compressor. I'm only getting 5volts at the compressor coil and my coil is not kicking in.
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Old 07-29-2008
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The PCM (pin 69) grounds the A/C clutch relay coil via the pink/yellow to direct power to the A/C clutch field coil. If you have only 5 volts across the compressor coil, check the A/C compressor clutch diode and relay (underhood box). Also, check the ground point at the front left corner of the engine compartment.
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Old 07-29-2008
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Quote:
Originally Posted by rwenzing View Post
The PCM (pin 69) grounds the A/C clutch relay coil via the pink/yellow to direct power to the A/C clutch field coil. If you have only 5 volts across the compressor coil, check the A/C compressor clutch diode and relay (underhood box). Also, check the ground point at the front left corner of the engine compartment.
Bob, pin 69 on the PCM is the signal for the WOT relay. The N/C contacts are used for this relay, so the AC compressor will have power without this relay picked. Also, if the suppression diode (across the clutch coil) is dropping the voltage to 5V, the fuse will blow!

The pressure switch contacts may have high resistance causing the clutch voltage to be low.......

Last edited by Takeda; 07-29-2008 at 09:31 AM.
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Old 07-29-2008
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Quote:
Originally Posted by Takeda View Post
Bob, pin 69 on the PCM is the signal for the WOT relay. The N/C contacts are used for this relay, so the AC compressor will have power without this relay picked.
Nope, the 2005 Ranger uses a NO relay, closed on a ground command from the PCM.


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Originally Posted by Takeda View Post
Also, if the suppression diode (across the clutch coil) is dropping the voltage to 5V, the fuse will blow!
Depends on the current flow.


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Originally Posted by Takeda View Post
The pressure switch contacts may have high resistance causing the clutch voltage to be low.......
The high and low pressure switches are not in same circuit as the compressor clutch solenoid in the 2005 Ranger.
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Old 07-29-2008
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Originally Posted by rwenzing View Post
Nope, the 2005 Ranger uses a NO relay, closed on a ground command from the PCM.


Depends on the current flow.


The high and low pressure switches are not in same circuit as the compressor clutch solenoid in the 2005 Ranger.
Bob, you probably have much less than 1 OHM back to the battery, and dropping 7V....the fuse will blow!!
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Old 07-29-2008
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Originally Posted by rwenzing View Post
Nope, the 2005 Ranger uses a NO relay, closed on a ground command from the PCM.

.
My bad, I was looking at an earlier year! The earlier years used a WOT relay in series with the AC clutch.
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Old 07-30-2008
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So which pin sends voltage to the relay in the fuse box? I'm only getting 5 volts at the compressor and I need to know if the PCM is putting out that much or if I have voltage drop somewhere between.
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Old 07-30-2008
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Originally Posted by 2005Edge View Post
So which pin sends voltage to the relay in the fuse box? I'm only getting 5 volts at the compressor and I need to know if the PCM is putting out that much or if I have voltage drop somewhere between.

The PCM provides the GND on the coil of the relay to pick it. It's possible that the relay contacts are bad, causing the big voltage drop. Since they are cheap, I would try replacing the relay first.
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Old 07-30-2008
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I swapped out the two relays and it's the same so there is not a relay problem.
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Old 07-31-2008
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Originally Posted by 2005Edge View Post
I swapped out the two relays and it's the same so there is not a relay problem.
Next thing is to measure the voltage at the relay contacts, if the voltage is still low there, work back to the fuse, etc. .....
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  #13  
Old 08-04-2008
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There is not accountable voltage drop across the relay or fuses. I need something from the PCM to see which way I need to go with it.
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