Not a circuit problem with a circuit code Pacifica

Justin Mobile Technician Utah Posted   Latest   Edited  
Case Study
Emissions
2017 Chrysler Pacifica LX 3.6L (G ERC Gas) 9-spd (948TE) — 2C4RC1CG8HR627463
P0390 — Camshaft Position Sensor "B" Circuit Bank 2

This is a case study to show how code description can lead you down the wrong path. 

This shop called me to help with the diagnosis on this vehicle. The vehicle is a 2017 Chrysler Pacifica with the 3.6L engine found in many Chrysler products. P0390 with a code description of “camshaft position sensor circuit-bank 2 sensor2” Code sets as pending as soon as you clear codes and restart the engine. One key cycle and the code sets as active and turns the MIL on. They had already swapped the left and right bank sensors with each other with no change.

I started with vehicle scan using witech with a micropod. I saved the vehicle health report and attached it here. No programming updates available for the PCM. Verified the code sets as described. A visual inspection of wiring and harnesses came up with no problems found. No hangers misplaced or loose. Nothing looked to be rubbing. 

Out comes the scope with a wiring diagram researched I test the signal at the sensor. I used a single channel and watched it live while cranking the engine. I see a pattern of zero to 5 volts. It looks clean and shows a varying pattern. Move my lead to the connector at the PCM. Same pattern. This is where I made the mistake. I called a PCM on this one. No need to chastise me here. I return when the new part arrived to program and setup the new module. Jump through all the hoops and hit the key. Yep same code returned. Merry Christmas to me. I inform the shop owner of my mistake and proceed to testing again. This time I grab all 4 leads on the scope and grab crank as well as 3 cam sensors. It didn’t take long to see the issue. One of the pull down signals was missing on the cam sensor in question. The missing pull down is at the 210 degree point in my picture. Pics provided as well as known good and broken car pico files. 

I payed for the PCM and did not charge the shop or the customer for the programming. Ate my humble pie and said my sorrys. So lesson learned. Hope this helps others that might be looking at a similar problem in the future. Oh and by the way, this is not a common fault problem. The parts house selling parts off code descriptions will never fix this one. The repetition of the pattern proves it isn’t a sensor or wiring problem. 

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James Technician
Indiana
James Default
 

Justin, help me understand what you're saying here. I see the fault in the waveform, but I don't see the fix. Did you fix this one? I know that a signal that is out of time or not what the PCM expects to see can result in a circuit fault code being set. Is this a problem with the reluctor on the cam then? Jim

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Justin Mobile Technician
Utah
Justin Default
 

The shop was closing today at 2:00 for the holiday. The repair will be made when the shop opens again. There wasn‘t enough time today to remove the valve cover for a visual inspection. Yes the problem is the reluctor.

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James Technician
Indiana
James Default
 

Thank you. If possible, please post a picture of the faulty camshaft. Jim

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Justin Mobile Technician
Utah
Justin Default
 

Not very often do I get to see the repaired vehicle as a mobile tech. If I’m lucky I get another call to the same shop when they have it apart. If that happens I will get pictures and share.

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Automotive Owner
California
Automotive Default
 

Here's one. The reluctor is sealed inside of a ring so you can't see any teeth/notches. Kind of boring!

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Dmitriy Analyst
Ontario
Dmitriy Default
 

Is it a magnetic encoder or an actual reluctor (ferromagnetic, passive) wheel?

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Automotive Owner
California
Automotive Default
 

Unknown.

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Andrew Technician
Minnesota
Andrew Default
 

It's a magnetic encoder, same as on a wheel bearing with an active wheel speed sensor. You can view the "teeth" with magnetic viewing film. The sensor is described this way in SI "The sensor detects magnetic flux changes between the peaks and valleys of the tone wheel attached to the camshaft", so there are no physical teeth, only magnetic. An issue we saw last year was the customer (owned a…

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Dmitriy Analyst
Ontario
Dmitriy Default
 

Great info; thank you, ATG and Andrew!

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Brian Instructor
Ohio
Brian Default
   

Thanks for posting the picture of this system!

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Automotive Owner
California
Automotive Default
   

Hi Justin. Great catch! Well, the post didn't say what the final verdict was, but I assume it needed a new CMP trigger (which = camshaft). If my assumption is correct, we've seen it before (see attached - circled area is an extra downward blip that set a P0369). One extra word of caution on these: The single sensor housing contains sensors for intake and exhaust, so it's hard to know which is…

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Justin Mobile Technician
Utah
Justin Default
 

Yes it is confusing. This is bank 2 sensor 2 which is the intake.

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Stuart Mobile Technician
Illinois
Stuart Default
 

Thanks for sharing​.​Lesson learned here is always dig out the scope and do a thorough diagnosis which is a hard sell these days but a nessesity​.​Not getting paid for a diagnosis is still cheaper than replacing and eating unnesessary parts.

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Geoff Diagnostician
Hawaii
Geoff Default
   

Excellent example of the failings of ECM logic when a mechanical fault exists. The PCM just knows the signal is wrong, so it sets a circuit fault. I bet some engineers will even say this is "not their fault" because we are supposed to rule out mechanical problems first before troubleshooting a DTC. Yeah, sure, lets disassemble everything every time. Sheesh. thank you and Merry Christmas, Justin.

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Ray Diagnostician
Ontario
Ray Default
 

Thank you Justin for posting and Merry Christmas! Ray

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Caleb Diagnostician
Indiana
Caleb Default
 

Good job Justin. Thanks for showing this. It's nice to know I'm not the only one who makes mistakes lol. I'm not saying this is an excuse to make more,but a drive to be better. Merry Christmas!

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Justin Mobile Technician
Utah
Justin Default
 

Anyone who acts like they never make mistakes is one of three things, a liar, a damn liar or not very experienced. We need to get away from the notion that making mistakes makes us weaker. It doesn’t. It’s how you deal with those mistakes that makes the difference. Trolls and scum point out others mistakes to make themselves feel better.

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Brad Owner/Technician
Illinois
Brad Default
 

Seems these reluctor wheels are sensitive. One of my techs touched one with a magnet and erased part of the wheel. That was a new one to us

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Edwin Mobile Technician
South Carolina
Edwin Default
 

Thanks Justin for putting this up. Its not a mistake in my book but a learning experience. You learn from the experience then go from here. Good job on this and if i was a shop owner i would be calling you back as you are a thorough technician. Happy New Year to you my friend.

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Justin Mobile Technician
Utah
Justin Default
 

Thank you Edwin.

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Michael Mobile Technician
Utah
Michael Default
 

In our industry the biggest part of mistakes is that it puts one in a moral dilemma. No other industry seems to care. We as technicians and business owners feel that it is wrong when we charge for parts that were not needed. If service information and testing brings us to the conclusion a part is faulty and it does not correct the issue, what then? Some customers will understand and be willing…

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Bob Owner/Technician
Massachusetts
Bob Default
 

Mike, I've always wondered how the auto industry got saddled with this issue but no other trades. If a carpenter quotes a job and then finds rotted wood after removing some sheetrock, well that gets added on to the bill. He missed it during the quote but now that it's found, that's going to be extra. I see it with plumbers, electricians etc. Any missed problems, surprises or unexpected work is…

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Justin Mobile Technician
Utah
Justin Default
 

I think for me the difference is this was a misdiagnosis as opposed to a job that you misquoted. A misquote would be fine to add the additional parts found when digging into the job. Selling parts that aren’t needed is theft. So if I misdiagnose and put a part on that isn’t broken I feel it’s stealing from the customer. No different than selling ball joints that aren’t worn out to get a sale and…

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Ben Mechanic
South Carolina
Ben Default
 

We can all identify a bit I'm sure. Not a clean catch, but got it on the first bounce isn't so bad in the car repair business. Much as we'd all love to bat a 1000, it's not going to happen. Not sure if you see what we see but your post came off as a tad confusing. I think something got deleted. I see: "....o files. The missing pull down is at the I payed for the PCM and did not charge the…

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Justin Mobile Technician
Utah
Justin Default
   

Edited the original post.

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Ben Mechanic
South Carolina
Ben Default
 

Same for me in the middle screenshot. "The missing pull down is at the....." nothing. "at the" what?

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Justin Mobile Technician
Utah
Justin Default
 

Got it. Nothing is left out. I somehow wrote the same line twice. I corrected the original.

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Ben Mechanic
South Carolina
Ben Default
 

Thanks! I was starting to wonder if it was me. Reads much better now.

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Ray Diagnostician
Ontario
Ray Default
 

I think using the Math Duty Cycle on cmp sensors could help find intermittent missing cmp pulses, as in the first GIF. The second GIF shows the similarity of the good cmp signal Duty Cycles.

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Justin Mobile Technician
Utah
Justin Default
 

I like it. Good test.

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