Help with p0340

[Stiforlife]

Hello everyone. I recently bought my daughter her first car. 2011 Fiesta. We bought it knowing there was a cel for p0340 camshaft position sensor malfunction. I did the easy stuff first and replaced both sensors since they were only $30 each. Reset the codes and they came immediately back on. So this time I decided I would test the sensors incase I was sold bad ones. There are 3 wires that go into the sensor. I believe one is power, one is ground and the other should be a signal wire back to the ecu. With the car on but not running I should see 12v between the power and ground wires but I'm not. And I have that situation with both sensors. As far as I know there isn't a fuse for the camshaft position sensors. So I'm assuming there is a bad wire somewhere and that's why the sensors aren't getting the 12v they need. Anyone else ever experience this? Thanks in advance.

 

[Handy Andy]

Can you test to see if the "ground wire" is hitting ground - an ohmic check would show less than 1Ω resistance on the ground wire itself - when checked to frame ground or battery post negative.

So, if you're able to retest and check the power wire at the harness to frame ground and it shows 12V - and across it to ground at the harness - it does not - then you know you have an open wire circuit.

 

[Stiforlife]

That's what I was afraid of. When I test for resistance from the ground wire of the harness to the negative post I get an open circuit. Just super weird I'm getting the same result from both sensors.

 

[Handy Andy]

Ok, the only way to find the "ground is thru two options, one is to trace the wire back thru the harness to the block - it should have a ground point close to it - so you don't have to snake thru a ton of wire to find any "exit hole" in the loom and find the bolt it goes to ground the wires in the harness. Usually these are Black Green stripe and are considered true chassis/earth ground so they are "ground" all the time.

Fiestas have three types of grounding - constant (that Black Green Stripe) switched (Black with Yellow) or Electronic (Black with Blue stripe).

So it pays to know which wire in the 3 wires are true ground. Since this is a PCM issue (the PCM need this data to work) then the ground wire and open circuit even at the engine block means something may have struck or rubbed against the loom or even eaten thru the soy-based insulation...

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It is possible the wire inside the harness is compromised, but I think it would be prudent to locate the REASON this ground failed, so you can correct it and it won't leave you or your family stranded.