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2008 Kia Optima 2.4l 4 cyl
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Discussion Starter #1
I'm working on a family members optima trying to get it back up and running after it just didn't start back up the other morning. She says it barely started when she last drove it on her way home. Pulled codes with my scanner and got a P0340 code. At this point, I have replaced the camshaft position sensor and tested the harness with my multimeter. I've verified good ground at the middle pin, 12v on the right pin, and 5v on the left pin. I'm not sure where to go from here. The car has 200k miles on it.

Any advice?

Thanks!
 

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2011 Forte SX 2.4L (thankfully MPI) A/T 144K miles
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1,398 Posts
So after you erased the P0340, it comes back immediately while cranking?
 

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2011 Forte SX 2.4L (thankfully MPI) A/T 144K miles
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Did you test the wiring while back probing the cam sensor connector with a helper cranking the engine? If not, you might want to try that if you can, because whatever is going on with that circuit might only be happening when everything is fully energized with the key at start.
 

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2008 Kia Optima 2.4l 4 cyl
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Discussion Starter #5
I just did this. While cranking the 5v stays solid. The 12v side drops down to about 10v and goes back to 12 when cranking stops. Should it stay at 12?. I’ve got the battery on a charger right now.
 

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2011 Forte SX 2.4L (thankfully MPI) A/T 144K miles
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A battery issue seems like a possibility. What was the static battery voltage before you put it on the charger? How old is the battery (not that it always matters though), and did you have it tested recently on a parts store machine?
 

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2008 Kia Optima 2.4l 4 cyl
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Discussion Starter #7
It was just under 12 volts. I haven’t had it tested yet but maybe that should be a next step. It’s at least a couple years old.
 

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2019 Kia Sportage. SX with AWD. 2.0L Direct Injected Turbocharged & Intercooled Gas.
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Just had a glass mat battery from Costco fail....only 2 years and 2 months old!
It happens!
 

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99 Kia Elan 1.8L, 17 Ford Edge Sport 2.7L V6, 15 Mustang 3.7L V6, 08 Harley Nightrain
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Just had a glass mat battery from Costco fail....only 2 years and 2 months old!
It happens!
Yes it happens, but at least Costco have one of the best replacement warranties.
 

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2008 Kia Optima 2.4l 4 cyl
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Discussion Starter #10
Battery charger says it’s fully charged now, still having the same issue. I tried jump starting just to eliminate any possible battery issues and still nothing. Any ideas?
 

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99 Kia Elan 1.8L, 17 Ford Edge Sport 2.7L V6, 15 Mustang 3.7L V6, 08 Harley Nightrain
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This is a tricky code.


There are significantly less likely causes for P0340 as well. These include the PCM failing or the Crank Sensor failing. You’ll need to check the voltage at the camshaft sensor to see if it is within spec.
 

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2011 Forte SX 2.4L (thankfully MPI) A/T 144K miles
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I would try another back probe test of the wires at the sensor connector, including the signal wire. You of course won't get a meaningful reading from the signal wire using a multi-meter, but it should be at least showing an 'averaged' voltage somewhere around 5V or so while cranking, which would confirm that the sensor is at least sending voltage on that wire. After doing that, if everything seems ok, you can run the same testing at the crank sensor connector. If both sensor's wiring pass all of that, then about the only things left to try is testing with a scope to check how the waveforms look, and checking for continuity of the signal wires from the connectors back to the ECM.
 

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2011 Forte SX 2.4L (thankfully MPI) A/T 144K miles
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It's hidden from sight on the right back side of the engine. Put your right hand on the upper right side of the engine and move it down the back side through the maze of wires. Feel with your fingers for a wire that disappears under a metal plate, around 1 foot down from the top. There's also a bolt just to the left of the wire, which is the retaining bolt for the cover. Trace the wire back up to find the connector. You could also find it using a mechanic's mirror, using the location described above.
 

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2008 Kia Optima 2.4l 4 cyl
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Discussion Starter #15
I tested the crank sensor and have 12v on one side, 5v on the other, with a good ground in the middle just like the cam sensor. I guess it could be a faulty sensor so I may look into swapping that out before I look into the ECM wiring.

is it at all possible the timing chain jumped some teeth?
 

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… is it at all possible the timing chain jumped some teeth?
Although almost anything is possible, I don't think a physical issue like that could be causing the P0340. That code is supposed to be limited to an electrical problem with one of the sensor circuits, which could include everything from the battery to the ECM.

Did the owner say anything about the CEL being on prior to the start of this current problem? We've all just been assuming the no-start is a result of whatever is causing the P0340, but now I'm wondering if perhaps that's not the case. Some vehicles need the cam sensor signal to start, but many do not (no idea about the Optima). If you have the time, try spraying a small bit of sensor-safe starter fluid into the intake to see if it will start and run for a few seconds on that outside fuel. If it won't start that way, then IMO it would also be a good idea to confirm there's no spark at all.

The problem could very well be a bad crank sensor, but that's going to be a bit of a PITA to replace. I'm just looking for some easy things to try, in order to rule out some possibilities we haven't been considering, before you have to get into the more time consuming work.
 

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2008 Kia Optima 2.4l 4 cyl
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Discussion Starter #17
Update on this. Today I pulled a spark plug and verified it does have a good solid spark. So maybe this code has nothing to do with the no start as you stated. I pulled the cover off for the fuel pump in the trunk and I can definitely hear it running/priming when they is turned on. Should I be testing for fuel pressure next?
 

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Update on this. Today I pulled a spark plug and verified it does have a good solid spark. So maybe this code has nothing to do with the no start as you stated. I pulled the cover off for the fuel pump in the trunk and I can definitely hear it running/priming when they is turned on. Should I be testing for fuel pressure next?
Check if the injectors are getting pulsed.

Spray starter fluid down its throat, and if it starts with that, then focus on fuel delivery, if no start then likely crank and cam position signals are off - check compression and timing (chain so less likely a problem).
 

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2008 Kia Optima 2.4l 4 cyl
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Discussion Starter #19
Resistance looks good at about 16 ohms on the injectors. I get 12v to one side and 5v to the other on each injector with the key on. I’m assuming this is normal. I’ll try some starter fluid down the intake and see what happens.
 

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Resistance looks good at about 16 ohms on the injectors. I get 12v to one side and 5v to the other on each injector with the key on. I’m assuming this is normal. I’ll try some starter fluid down the intake and see what happens.
With only the ignition on you should 12v on both sides.

Check if you're getting pulses on the coils when cranking.
 
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