Not a circuit problem with a circuit code Pacifica
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.
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
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.
Thank you. If possible, please post a picture of the faulty camshaft. Jim
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.
Here's one. The reluctor is sealed inside of a ring so you can't see any teeth/notches. Kind of boring!
Is it a magnetic encoder or an actual reluctor (ferromagnetic, passive) wheel?
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…
Thanks for posting the picture of this system!
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…
Yes it is confusing. This is bank 2 sensor 2 which is the intake.
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.
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.
Thank you Justin for posting and Merry Christmas! Ray
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!
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.
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
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.
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…
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…
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…
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…
Same for me in the middle screenshot. "The missing pull down is at the....." nothing. "at the" what?
Got it. Nothing is left out. I somehow wrote the same line twice. I corrected the original.
Thanks! I was starting to wonder if it was me. Reads much better now.
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.