2008 CMP circuit - PowerStrokeNation : Ford Powerstroke Diesel Forum
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post #1 of 16 (permalink) Old 09-18-2014, 03:29 AM Thread Starter
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2008 CMP circuit

I have a 2008 which I recently converted to a cummins 5.9 common rail. After the conversion everything on the truck worked peachy until one day the tachometer stopped working, as did the A/C.

Both the ford cam and crank sensor are adapted onto the cummins to allow the Ford "smart dash" to function.

I get a consistent P0341 in the ford pcm for "Camshaft Position Sensor A Circuit Range/Performance (Bank 1 or Single Sensor)"

I chased the P0341 according to https://www.motorcraftservice.com/pu...15/V8E5093.HTM


everything checked out until I got to V4 "CHECK THE CMP CIRCUITS FOR A SHORT TO VOLTAGE IN THE HARNESS"

where i find 2.5V at both + and - terminals of the cmp connector (Key on, engine off, sensor unplugged)

If voltage is found the chart says to locate the short to voltage in the harness.

I separated the harness and isolated the pair of wires for the cmp connector.

Under the tape, the pair of wires is sheathed in foil along with a bare wire which goes through the pcm connector and to ground, this is factory ford portion of the harness.

I checked for continuity between the two wires for the sensor while bending and jiggling the length of the harness and there was none. No damage to any of the wiring or signs of heat/ chafing.

I checked for continuity between both sensor wires and the bare wire and there was none.

There is never any voltage at the bare wire.

No bent pins or signs of heat in the pcm connector.

Voltage at two pins which should have 0.

Is this PCM internally shorted or otherwise damaged somehow?

I don't understand where this 2.5V is coming from.

This system all worked fine for a thousand miles or so.
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post #2 of 16 (permalink) Old 09-18-2014, 08:39 PM Thread Starter
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Re: 2008 CMP circuit

Really I guess what I need to know is whether 2.5V at pins 7&8 with KOEO is indicative of a problem of if i should be looking elsewhere. .
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post #3 of 16 (permalink) Old 03-10-2018, 08:20 PM
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Hey I know this is a long shot but I am having the exact same problem with my ford with a 12 valve same year and exact same voltage in the pins. Did you get yours fixed? I tried a new ecm and that wasn't the problem. My tach hasn't worked since I did the swap
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post #4 of 16 (permalink) Old 03-10-2018, 10:30 PM
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Re: 2008 CMP circuit

That information he got is probably wrong. It sounds like he was reading the bias voltage in the circuit.

How many wires is the sensor? Two or three?

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post #5 of 16 (permalink) Old 03-11-2018, 06:09 PM
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It's a 2 wire sensor. It's the factory ford cam sensor. When I probe the pins on the harness side there is suppose to be no voltage according to the pin point test that ford has for that p0341 code. And I'm seeing 2.5 volts on both pins. So when I probe pin 7 and 8 I see the same voltage there with the engine pcm bulk head disconnected off the pcm. My tach won't work. This is so frustrating. Everything worked before I pulled the blown engine out of it.
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post #6 of 16 (permalink) Old 03-11-2018, 06:48 PM
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Re: 2008 CMP circuit

That's just a bias voltage, it's not a problem, that pin point thingy is wrong. Back probe both wires at the pcm, switch the meter to ac voltage and crank the truck. You should see around .8 volts ac.

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post #7 of 16 (permalink) Old 03-11-2018, 06:49 PM
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Re: 2008 CMP circuit

Oh wait. You see voltage there with the pcm disconnected? That's weird. We'll come back to that later I guess. First check for a signal.

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post #8 of 16 (permalink) Old 03-11-2018, 07:26 PM
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Yes there is less then 1 volt ac during cranking. The pcm has two bulk head connectors when your facing the pcm I left the left one hooked up and unhooked the engine wiring harness. Then put one lead off the meter on pin 7 which is cmp + and put the negative lead of the meter on the ground of the battery and I'm seeing 2.5 volts. And I did the exact same thing with pin 8. Which is cmp -. I don't quit understand the bias voltage thing. According to v 4 if there's any voltage present there is short to voltage? Maybe I'm misunderstanding the pin point test
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post #9 of 16 (permalink) Old 03-12-2018, 01:31 AM
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Re: 2008 CMP circuit

The connector you were measuring from was unhooked?

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post #10 of 16 (permalink) Old 03-15-2018, 02:49 AM
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Re: 2008 CMP circuit

When I did the crank test to measure the ac voltage of the cam sensor it was unhooked from the cam sensor and I measured that off of the sensor itself, and for the v 4 test. The connector off the pcm was unhooked for the engine harness, and there is no voltage off of the cmp pins. But I'm getting the voltage at pin 7 and 8 directly off the pins off the pcm.
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