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2005 chevy trailblazer_ls
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Discussion Starter #1
Chasing a P0340 gremlin. A new sensor didn't fix it. Checking voltage, the red wire has 12v, the pink wire is grounded, the brown wire is supposed to be 0v/12v signal wire, according to a website I was reading, but I'm getting a steady .3v. I traced wires almost to the PCM. I unplugged the grey and white PCM connectors one at a time. If white is unplugged, I get 0v. If grey is unplugged, I get 12v. Is there any chance that the PCM is the culprit, or do I need to cut open the rest of the wiring harness and look for the problem?
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2002 chevy trailblazer_lt
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Based on reading the code definition I would say the value on the signal wire is a rapid pulse, not a steady voltage. Depending on your meter you may not even see it. I have a PID for use in Torque or OBD Fusion that displays what I believe is the pulse counter. 'CMP Active Count' is what the tech2 calls it if memory serves.
 

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Discussion Starter #3
Yes, the site i was looking at was saying to have key on, engine off, then turn engine by hand to find the signal point. It should have been either 0v or 12v depending on where it was on the rotation. I turned it over a few times, and never found the 12v point, and it was never reading 0v.
 

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Do you have access to wiring schematics? That would identify the connections at the PCM allowing you to test the wires of steady continuity. Sometimes harness connectors have a pin loosen inside.

The conditions for setting that P0340 indicate a 3 second time period elapses where the pcm does not see a cam pulse

Screenshot_20200509-091123~01.png
 

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Yes, the site i was looking at was saying to have key on, engine off, then turn engine by hand to find the signal point. It should have been either 0v or 12v depending on where it was on the rotation. I turned it over a few times, and never found the 12v point, and it was never reading 0v.
Ah, you have read more than I in this case! I just backprobed mine and saw 9 volts but didn't turn the engine.
 

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Discussion Starter #7
I did find this on a Google search. I'll have to check it out later to see if there's a loose pin. But I still don't see why there would be a steady .3v coming from the PCM.
img052.jpg

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I just rechecked mine. I got either 9.67 volts or 25 millivolts (which is roughly the same as your .3 volts?). It was either one or the other never something else.
 

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Discussion Starter #9
Interesting. Thank you. I guess I'll see if another brand of cam sensor fixes it. I did change out the sensor under warranty, but was the same brand/part number as the one that lasted 3+ years.
 

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Discussion Starter #11
Thats exactly my problem. I'm getting that .3v with or without the sensor plugged in.
 

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I have noticed that the PCM wiring is not the same year after year, at least my schematics indicate differences. With this in mind I would proceed with a bit of skepticism when looking at schematics that may or may not be correct for your vehicle.
 

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Discussion Starter #15
Ok. Then if it's normal, I'll try a different brand and see how it goes. Thank you.
 

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So in the big picture....the vehicle runs but occasionally sets this code? I see this code is defined as a type B DTC. These generally do not set the check engine light at first occurrance but requires maybe 2 consecutive occurances (drive cycles) to set
 

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This 2004 schematic appears to match your online reference. I don't have an 05 diagram but my 06 diagram shows different pinouts.

Screenshot_20200509-102644~01.png
 

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Discussion Starter #18
Yes, first start it sets a pending code, second start it sets it as confirmed. Every time. Yes, it drives, but it causes a hard start, and having cruise control would be nice.
 

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Discussion Starter #20
Yes, the 06 is different. But thank you for all the help. Unfortunately, ACDelco is an order only part for all of the different stores in my area.
 
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