Cam Signal Inverted

Jerry Technician New York Posted   Latest   Edited  
Resolved
Driveability
2013 Subaru Impreza WRX 2.5L (EJ255) 5-spd (TY758)
P0018 — Crankshaft Position - Camshaft Position Correlation Bank 2 Sensor A

Attached is a screenshot of cam crank correlation, I don't understand why cam sensor is inverted on green trace, checked with 2 different scopes, does anyone know if it would effect anything and what would cause this

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Gerald Owner/Technician
Missouri
Gerald Resolution
 

If your only getting the p0018, the computer is happy with the signal, just doesnt like its timing

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Pat Diagnostician
Indiana
Pat Default
 

I have seen this happen particularly on Nissan Titans due to a faulty power relay. Here is the before and after.

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Jerry Technician
New York
Jerry Default
 

Was it causing a running problem or throwing a code?

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Pat Diagnostician
Indiana
Pat Default
 

The vehicle was a crank no start. The battery was dead so I when I did a code scan there was nothing present. But you can see the voltage fluctuations in the blue cam trace. Your signals look pretty strong. I was just posting as something to keep in the back of your mind.

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Jerry Technician
New York
Jerry Default
 

THANK YOU

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Justin Mobile Technician
Utah
Justin Default
 

I had a 2005 Subaru that I was working with yesterday that would flip one of the cam signals consistently when you would raise the RPM over 1500. Below 1500 it would be like your red trace and over 1500 it would look like your yellow trace. It had correlation codes on both banks but only one would flip. I determined the problem was not likely the from the pattern as only one bank would change.

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Geoff Diagnostician
Hawaii
Geoff Default
 

Justin, what fixed that one? Chains, or the TSB ECM update?

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Andrey Owner/Technician
Washington
Andrey Default
   

Do you know any repair history for this car? This engine have four camshaft sensor, how many of them have inverted signal?

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Jerry Technician
New York
Jerry Default
 

This nengine only has 2 sensors, left and right, the left sensor is inverted

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Hollis Technician
Colorado
Hollis Default
 

Did you see TSB NUMBER: 11-127-13R it has applicable diagnostic info for P0018. [INTRODUCTION This Bulletin announces a diagnostic procedure and the availability of updated ECM reprogramming files to address DTCs P0017 and P0019. The diagnostic procedure is also applicable to DTCs P0016 and P0018. ]

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Stephen Technician
Tennessee
Stephen Default
 

I have seen one where the sensor gap effected the “polarity”. The signal can be checked KOEO by aligning a tooth with the sensor and check the output voltage of the sensor. Then align a notch with the sensor and check the output there. As to whether it’s a problem depends on how the software is instructed to read the signal. If it only looks for a transition, I would expect normal operation. If…

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Caleb Diagnostician
Indiana
Caleb Default
 

Can you swap the sensors and see if the problem follows?

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Christopher Owner/Technician
Arizona
Christopher Default
 

I had this happen years ago..on some j1850 chrysler ecm's...late 90s early 2000 and a ford once and a nissan (older)years ago.....was pcm each time

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Bob Owner/Technician
Massachusetts
Bob Default
 

Jerry, I had a hyundai that did something very similar. 3 different aftermarket sensor were put in it and they all would invert themselves at different times. The ultimate fix was a factory new sensor. Also, an inverted pattern will absolutely throw your correlation off. The computer is looking for either a rising or falling edge. If it's inverted that edge happens at the wrong time. Here's a…

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Geoff Diagnostician
Hawaii
Geoff Default
   

I agree with Steve and Bob. Some signals will flip and the ECM doesn't care, some will flag a DTC. I had a Nissan set a CKP DTC when the CMP was the signal upside down. People have argued it to death on both iATN​.​net and autonerdz​.​com but if you replace the sensor and it's fixed, well, then it's fixed. (!!)

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Jerry Technician
New York
Jerry Default
 

Thanks for all the replies I ordered a new sensor from subaru will see if it solves the problem

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Joel Diagnostician
California
Joel Default
 

Did you resolve the issue? did the cam signal was really inverted ?

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Jerry Technician
New York
Jerry Default
 

The dealer sensor read properly, but didn't solve the correlation code, another shop changed the timing belt and cam phasers with aftermarket, dealer phasers solved the problem

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Joel Diagnostician
California
Joel Default
 

Thank you

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