Cam Code - Need opinions and a know good cam crk sync

Bob Owner/Technician East Longmeadow, Massachusetts Posted   Latest   Edited  
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Driveability
2008 Hyundai Tiburon GT 2.7L (F) 5-spd (M5GF1)—KMHHN66F58U295650
P0340 - Camshaft Position Sensor "A" Circuit Bank 1 or Single Sensor

I have a cam sensor with some odd activity. I'm pretty sure It's bad but I would like to get some opinions on some of the sensor anomalies. The symptom is a Check Engine Light and code P0340. The vehicle starts and runs fine but the Cam Code sets on startup. Clear the code and restart the car and the code is already pending.

It would be great if someone had a know good cam/crk sync from a 2008. I can only find waveforms for 2004 and older and I don't know if they are the same.

There are two things that I see. First, the Cam sensor only reaches 4 volts. It is a 5 volt sensor that is supplied with battery voltage and ground. The crank signal does read 5 volts but not the cam sensor. I have good power and ground at the cam sensor but 4 volts out. I suspect this is a problem but would like opinions from others who have scoped a 2008 sensor.

There is another strange anomaly I have seen with the cam signal. The pulse width duration changes while cranking versus running. Another words, when cranking there are less crank pulses between the cams falling and rising edges than there are when the engine is running. On it's face that doesn't seem possible. Take a look at these zoomed in captures to see what I mean. (the CRK sensor voltage is skewed because I moved it up on the screen for a clearer view) 

This is a capture while cranking

This is a second capture cranking

And now here it is while running

As you can see there is a huge difference in these waveforms. I don't appear to be losing any crank pulses, it just seems that the cam sensor pulse width changes, which is strange because the trigger wheel can't change it's notch size as far as I know. I uploaded the full captures if anyone wants to look at them. In the bin files I also tagged the number 1 ignition wire and number 1 injector. It's a waste spark system.

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Darren Mechanic
West Allis, Wisconsin
Darren Default
 

I am comfortable with saying the sensor is bad. Should be 0 to 5volts period.

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Bob Owner/Technician
East Longmeadow, Massachusetts
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That's what I thought but this OEM graphic appears to show the cam is a 4 volt signal. That's why I was hoping to get a capture from a real '08 model car.

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
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Hi Bob: Perhaps I'm suffering from Cranial-Rectal Inversion but the Min/Max of the CMP in example graph shows the signal is 5 volts. Perhaps, you're chasing ghostes? What is the code set enable criteria (primary & secondary)? Without knowing that, I'd be more concerned with the signal issue/s that Tim described. As an aside, remember the hot Chrysler no-starts? Perfect square wave on the

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Bob Owner/Technician
East Longmeadow, Massachusetts
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The screen is set to 2v per division and the signal is 2 divisions high. That's 4 volts right? Are those captures real or just drawings?

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Chris Diagnostician
Lansdale, Pennsylvania
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Guido is right. If you look at the actual data to the right of the graph, you'll see it reads 5 v on the max. Misleading scope setup perhaps.

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Tim Curriculum Developer
San Diego, California
Tim Default
 

It's definitely the CMP sensor (or wiring). It should be high for a crank revolution and then low for one (50% duty cycle). In your '2nd' file, your CMP signal delays coming to life, and then only has a short drop every other crank revolution for a while. Then near the end, it drops every crank revolution. Also, for Hyundai & KIA, the position sensor code info has known good waveforms.

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Bob Owner/Technician
East Longmeadow, Massachusetts
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Hi Tim, I would agree with your comments, the signal definitely glitches when first cranking. It's kind of odd that if I disable fuel and crank it steady the signal pulse is short all the time but when it's running it looks normal. What do you think about the voltage level? This graphic seems to show that 4 volts is normal.

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Tim Curriculum Developer
San Diego, California
Tim Default
 

I find the published Hyundai & KIA waveforms to be very reliable. If it's glitching only during cranking, I'd measure reference voltage and sensor ground voltage drop as well. If the circuits are fine, sometimes sensors only fail only under very specific conditions. For example, a tiny bit of voltage drop may be normal based on what shares those circuits, and maybe it's just barely enough to

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Chris Diagnostician
Lansdale, Pennsylvania
Chris Default
   

I could be off base here but I'll give it a shot. Based off of Farradays law, an increase in resistance, in this case in the CMP sensor or it's wiring, should result in a delay of magnetic flux. In my mind this accounts for the delayed and/or strange reaction of the CMP sensor. I do agree the 4v is strange, but I also think it would be stranger to be able to have a perfect 4V square wave by

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Dmitriy Analyst
Toronto, Ontario
Dmitriy Default
 

Chris, it's a Hall effect sensor with a bunch of electronics on top of it, isn't it? No simple laws can explain its behavior then. Sometimes it switches, sometimes it doesn't -- especially at low rpms. When the car is running, rpms are higher, rate of magnetic field change is higher, so switching is more reliable.

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Bob Owner/Technician
East Longmeadow, Massachusetts
Bob Default
 

Dmitriy, I agree, these sensors can fail in weird ways. I have never seen it myself but i have seen others post captures of hall effect signals that inverted themselves. When I first looked at this I was only looking at the signal when the engine was running and the signal timing appeared correct. It was only after I realized that the code would set right at startup that I started to zoom in

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Chris Diagnostician
Lansdale, Pennsylvania
Chris Default
 

Dmitriy, You are correct, it was late and obviously I was a bit more tired then I thought. I didn't used to get tired, I must be getting old. Thank you for setting me straight, seeing as the principle of operation is quite literally the name of the sensor. Faraday's law only applies to EMI, which would only be useful if this was a variable reluctance sensor. Hall Effect doesn't utilize the

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Bob Owner/Technician
East Longmeadow, Massachusetts
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Chris, I will scope all the sensor wires together tomorrow and post up the results. If I'm reading that scope capture from hyundai correctly, the cam sensor output is 4 volts.

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Bob Owner/Technician
East Longmeadow, Massachusetts
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Today I scoped the sensor power and ground while cranking and starting and there were no issues there, so I installed a new cam sensor. At first I thought all was good because the signal looked normal cranking and running. However, i checked codes and found the P0340 again. I cleared the code and started and ran the engine multiple times. It turns out that sometimes when starting the code is

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Chris Diagnostician
Lansdale, Pennsylvania
Chris Default
 

Bob, This is a strange one, and you were right on with Dmitriy earlier, sorry for potentially sending you off into the woods before, wasn't thinking. Going to have to think on it. Is the ATS software available to read scope files the same way Pico and Snap-On do? I see a lot of people are using the ATS set up and it intriques me. Thank you

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Bob Owner/Technician
East Longmeadow, Massachusetts
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No worries Chris. This one is starting to get weird. At this point I'm thinking I need to try a factory sensor. You can download and use the Escope program in demo mode to view any files. drive​.​google​.​com/file/d/1mqKhkI… automotivetestsolutions​.​com/software-updat…

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Chris Diagnostician
Lansdale, Pennsylvania
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Thanks Bob. I'm going to play around with that tonight and see if I have any eureka moments. I wish you luck with the OEM sensor tomorrow. Curious to see the change, if any.

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Dmitriy Analyst
Toronto, Ontario
Dmitriy Default
 

This gets more and more interesting. If the factory sensor does not help you might have to check if the camshaft got magnetized somehow...

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
Anthony Default
 

Hi Dmitriy: In all my years in the trade, I never envisioned the day when one may have to degauss a camshaft. Isn't life interesting? Guido

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Geoff Diagnostician
Lahaina, Hawaii
Geoff Default
 

Last time I heard that word I was ten years old and about to put speakers next to the television set. Dad said, "no!" and explained it all. Dad was an EE for Bell Labs / ATT / Lucent.

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Geoff Diagnostician
Lahaina, Hawaii
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I've never had one flip back and forth, but I had upside down wave on a Nissan once and a new sensor fixed it. Crazy part was that, although the CMP wave was upside down, it was setting a CKP DTC. New CMP sensor fixed it. I really would like to figure out some day if all these new sensors were broken when they left the factory, or they were mishandled by the convoluted supply chains we all

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Bob Owner/Technician
East Longmeadow, Massachusetts
Bob Default
 

Update: I couldn't get a factory sensor right away today so I picked up another sensor from another supplier. Different brand but I suspect it's probably the same as the others. This car is from a used car lot I do a lot of work for and they already replaced the sensor once and I have now put 2 more in it. I did check the shaft for being magnetized. I don't know how scientific I was but I tried

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Dmitriy Analyst
Toronto, Ontario
Dmitriy Default
 

Can't wait to see what happens when the factory sensor is installed. You are sitting on a treasure trove -- all possible Hall effect sensor failures in one case. I have yet to see a good explanation how Hall effect sensors get their signals inverted, but we know that happens and some cars even get firmware updates to deal with the issue (have you checked TSBs, by the way?)

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Bob Owner/Technician
East Longmeadow, Massachusetts
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UPDATE - Conclusion Ok I can now wrap this up. As I'm sure everyone suspected, the fix was a new factory cam sensor. The first thing I noticed right away was that the factory sensor signal was a full 5 volts instead of 4. Several guys mentioned the signal should be 5v and of course they were correct. I have never seen or heard of a 4v signal however, after putting 3 different sensor in that all

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Anthony Technical Support Specialist
Kirkwood, Pennsylvania
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Hi Bob: I'm glad that you made a …e study out of it. I understand that was not what you originally intended. I have a slight correction to make though. "...those aftermarket sensors for free because they have a minus value." Guido

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Bob Owner/Technician
East Longmeadow, Massachusetts
Bob Default
 

" minus value" you're right. I thought of that after I posted it. Anytime you install a defective part, you lose money.

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Chris Diagnostician
Lansdale, Pennsylvania
Chris Default
 

Thanks for the update Bob, it is good to see it was just faulty parts. I was kind of looking forward to the thought of degaussing a cam though. It always throws one for a loop when a diagnosis is made based off sound data and testing, a part is replaced, and the fault remains. I am also glad this became a case study. I frequently get kick back for shying away from aftermarket as much as

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Dmitriy Analyst
Toronto, Ontario
Dmitriy Default
 

Great finale, Bob, so many lessons in this one. The scope capture in the service info is truly shocking. If we are supposed to believe that max of Ch 2 is 5V, then what about -4.8V (!) min on Ch 1? Who does that? Though 4V output didn't seem to be a problem for the vehicle to interpret (after all, 4V is more than 75% of 5V, so still digital "high"). The wrong signal signatures from the

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