S52 Camshaft Position Sensor

[rasmuw]

Is anyone aware of any camshaft position sensor changes between 1998 and 2000? FCP Euro lists part 12141703221 as valid up to 9/98, but the same part number is valid for cars after that. One source I've spoken to has suggested that early S52 camshaft position sensors were inductive and later were Hall Effect. I'm skeptical, thinking the parts suppliers would be aware of the change.

[bluptgm3]

Use the last seven of your VIN in www.realoem.com to determine your exact part number requirements.

[rf900rkw]

You don't just change from inductive to Hall effect without changing the control circuitry in the computer. The crank sensor changed from 5V to 12V supply. The cam sensor is the same for all single VANOS M/S52. Even the M50TU. FCP is just whacked. Again.

[rasmuw]

You don't just change from inductive to Hall effect without changing the control circuitry in the computer. The crank sensor changed from 5V to 12V supply. The cam sensor is the same for all single VANOS M/S52. Even the M50TU. FCP is just whacked. Again.

Thanks, Randy.

Understood about the control circuitry in the computer if a change were made. Knowing that the cam sensor did not change is the confirmation I needed.

In defense of FCP, when I called them it was after it had been suggested to me by an independent tech (who said that he worked on Z3) that the sensors changed in 1998. FCP lists that the cam sensor is up to 9/98, but they specify the same sensor thereafter. The sales person did not know why the listing is written as it is. Now I know that it was the tech who provided the misinformation.

[rf900rkw]

Ah. The M52 changed to the M52TU with a different sensor for 99. The S52 carried on through 00.

[ihm96]

That M52 to M52TU change has really screwed me up a few times, until I began to fully realize the differences and changed up how I researched before ordering parts. Sometimes I wish my car had the simpler M52 because it seems like theres more aftermarket there and some inherent rev hang in M52TUs because of the drive by wire (or at least thats how it was explained to me).

Ah. The M52 changed to the M52TU with a different sensor for 99. The S52 carried on through 00.

[tsick]

Hello, I have been reading these forums for a number of years now to help work on my 1998 M Roadster. A recent 065 fault code led me to an investigation of the camshaft sensor type and DME circuit for my car. It is MS41.1 and the cam sensor according to RealOem appears to be a Hall Effect Sensor. But the BMW Electrical diagram does not show a Hall Effect Sensor for camshaft position. It does for Crankshaft sensor. I have tested the circuitry by oscilloscope measurements and my DME does not produce a 5V signal necessary for Hall Effect sensor. It produces a sine wave signal which appears to change frequency between a reference signal and the sensor signal. A couple of site have described this method for Siemens DMEs. My dealer looked up the "correct part" and I installed it but the DME still does not recognize the cam sensor input. I have oscilloscope recordings of the sensor if anyone is interested. The cam signal is locked to the crankshaft signal but I cant interpret how the DME then interprets the signal coming from the sensor to determine cylinder 1 firing. Very confused. Have been looking for an explanation of the circuit now for many weeks. Recently post a new thread on the topic in the Z3 forum. Would be helpful if anyone had oscilloscope tracings from S52 MS41.1 cam sensor for refencence. Hard to know otherwise whether the DME is not producing the correct output signals to the sensor.

[bluptgm3]

That M52 to M52TU change has really screwed me up a few times, until I began to fully realize the differences and changed up how I researched before ordering parts.

All ya all know how to use www.realoem.com using the last seven of your VIN, correct?
This way you get to an accurate listing of parts/part numbers for YOUR car.

.....my 1998 M Roadster. A recent 065 fault code led me to an investigation of the camshaft sensor type and DME circuit for my car.

My dealer looked up the "correct part" and I installed it but the DME still does not recognize the cam sensor input.
Very confused.

Did you clear the code before additional interrogation? DME may not communicate with sensor until code has been cleared.

Sent from my iPhone using Tapatalk

[Adker]

Since you looked at the signal at the DME and it looked good, it points to the DME. Does the code return as soon as you clear it?
There should be a gap in the crankshaft sensors pulses, the DME knows where the gap is in relation to the crank angle. The DME detects the gap and then counts teeth to determine the position of the crank. The more teeth, the better the resolution. Since the cam and crank turn at 2x the RPM of each other, adding the CAM signal into the mix yields where each cylinder is on its journey through the 4 cycles.
https://www.picoauto.com/library/aut...ating-running/

[tsick]

Thanks for getting back. Here is what I have done so far. 1) checked continuity and for the presence of shorts from DME pinouts on connector (connector removed, power off). Found continuity for all pins to the appropriate cam and crank sensor connectors. No evidence of shorts to ground or between leads. With DME connected and powered (position II, engine not running) I get the appropriate 5V supply to crank sensor, but no 5V supply to cam sensor (but wiring diagram for MS41.1 does not show a supply out voltage). The black lead shows a 2.5 V signal from the DME but this goes away with the sensor connected. I scoped the signals by back probing the appropriate leads which could be identified in the splice box located centrally in the engine compartment. Verified these leads both from the DME and sensor connectors. When running I get a good crank sensor signal as described above (not surprising since the car starts and runs well). The cam sensor signal from both DME leads is a complex alternating pattern of changing frequency sine waves which are locked to the crank signal. The frequencies of the two signals vary between the two leads (hard to explain without seeing the signals all aligned. End result is that on startup the cam sensor circuit does not recognize the sensor, trips 065 code and the engine runs without cam input. Yes I routinely reset all codes before making tests but as 065 triggers at startup it is now always there. Note: I originally replaced cam sensor with OEM VDO sensor and it did not work (but actually did not always trip 065 every start up). I replaced the VDO with original BMW sensor from my dealer ($$$) and he verified based on my VIN that it was the correct sensor. Th BMW sensor seems to trip code more easily than the VDO sensor. I haven't directly compared the signals from the two sensors but my recollection is that they were similar as described above. So I am trying to find out if the DME is functioning correctly or there is a DME/sensor mismatch. Hope you guys can help. A poster on another forum reported almost identical findings for his 5 series (not sure of the year, but posted a link to the thread and some other interesting information on a new thread I started yesterday before I ran into this thread). Knew of Randy's expertise on these cars so I posted the problem here. Sorry this is lengthy.

[Adker]

I have the same engine/year so I will check the pins below but here is how I read the schematic.

Pin 1 = Power (12V?). Shows a limiting resistor in the sensor block diagram
Pin 3= Ground. Shows this in the pinout description of the DME, P43 Gnd
Pin 2 = Signal. This should have a weak reference voltage (5V?) on it that will be pulled to ground when the sensor is active. Connected to the solenoid symbol in the sensor block diagram

If the sensor shorted out, it could have damaged the power feed from the DME which would explain the strange results you are measuring.

[Adker]

Measures out like an inductive pickup. No voltage on Pin 1 like you would expect on a hall sensor, they need a power source to work.

Signal measure across pins 1 and 2. At idle get a stable sine wave +/- 1.2 volts. Note, divide voltage shown on bottom of screen by 10 ie 5V is really 0.5V. Freq is much higher I expected (102.9 KHz), need to see whats up with that.

Signals on pins 1 and 2 measure to pin 3(Gnd).
Pin 1 has a sine wave -0.7 to 3.1V (input trace 2)
Pin 2 has a sine wave +/- 1.2V (input trace 1)

[tsick]

Thanks Adker. That is exactly what I was looking for. My signals are a fraction of those and not stable sine waves. Suggests I might have a problem with my DME. Also possible the sensor is incorrect but the part number has been checked by both RealOem and my dealer parts dept. It is a 3 pin sensor which would suggest a Hall Effect sensor but is it possible that it is (or should be) inductive and the third pin is a ground being used for the shield. I will disconnect the sensor and apply 5v and see if it gives m a 5v out which goes to gnd near metal. I will also probe my sensor wiring versus the shield. Maybe one or more of the leads is making contact with the shied foil. I didn't check for a short to the shield previously. Will get back with results.

[Adker]

One of the pins is a Gnd but it is not a shield according the the schematic, it is a Gnd reference for the coil (inductor) inside the sensor. This looks like one of those one-off applications before cars went to using all hall effect sensors.

Before you try anything let me do a little more digging. The freq of the sine wave is way to high, I used the auto set to lock onto the signal but I need to manually lower the frequency of the scope to pick up any low freq signals. I was expecting something like this

Idle around 800RPM so Cam is 400RPM
Divide by 60 to convert RPM to seconds
Multiply by number of teeth the sensor detect per revolution.
So 400/60= 6.67 revolution per second. Not sure how many teeth up per revolution (1-30?) but the scopes shows a 100KHz signal and it should be orders of magnitude lower say 6-200 Hz.


Could be two signal going on at the same time, one high freq and a lower freq. The car is running perfect while these measurement are being taken so I am assuming everything is working as intended.

[tsick]

Hi Adker. The following was posted on the RomRaider forum (https://www.romraider.com/forum/view...p?f=42&t=14259). I haven't been able to find the document that was referred to, but the poster mentioned some Wiki files. "Cylinder Identification Signal: An angle pulse generator is used for the camshaft position sensing. The MS41.X ECM uses the signal from the camshaft sensor to set up the fully sequential fuel injection.
This sensor consists of two windings (primary and secondary) that are connected together at one end, and a magnetic core.
The primary winding is supplied with a 120 kHz AC signal. The magnetic coupling causes an induced voltage into the secondary winding (at the same frequency). However the induced voltage has a slight phase shift due to the induction time delay.
The trigger wheel of the camshaft influences the magnet field of the sensor and causes the phase shift to increase as the disc of the wheel moves closer to the sensor. The ECM monitors this change in phase shift as “TDC” (compression input) from the camshaft. When the disc passes by the sensor the phase shift moves closer again.
If this input is defective, the system will still operate based on the Crankshaft Position/RPM Sensor. A fault will be set and the ECM will activate the injectors in parallel. The camshaft position sensor is monitored as part of the requirements for OBD II". I suppose these are the high frequency sine waves you are recording. I believe if you look at a longer segment of the recordings to catch the cam disc passing the sensor, you will see a frequency shift. I see this in my signal clearly but the signal itself is not clean like yours. At my son's wedding in Indy so won't get back to this for about another week. Thanks for your help

[Adker]

I found the other signal, as stated above, it appears the sensor changes the high freq oscillation when it detects the cam (or vise versa). One picture is at idle and the other is with the engine reved. You can see the high frequency pulse duration shortens with increase RPM. I bet any change to the characteristic of this sensor (second source suppliers) could really effect the operation of this circuit. The DME does generate the 102.9 KHz signal sine wave I am seeing with the ignition on. The measurements below were taken with the scope across the sensor input (Pin1-Pin2) to the DME.

Found some info on the sensor operation, page 5, : http://www.rfdm.com/Daniel/MRoadster...nicsignals.pdf
Since it is using frequency shift , it will be very tolerant to noise from ignition, starter, motors etc. The coil packs are close to this sensor so that may be why it was used. Don't see this type of sensor used anymore.


Lived in Indy and Bloomington, small world, enjoy the wedding!!

[tsick]

Hello Adker. I am now in Baton Rouge house sitting for a few days after the wedding (Very nice in Indy). Thanks for the follow-up and good work. Especially glad to read the description of this sensor. I am posting a few of my recordings. The top trace is my crank sensor output. Typical Hall Effect Sensor with square waves and missing signals from the missing teeth on the flywheel. The middle trace is the sensor output to the DME on pin 2. Like yours it is an alternating pattern of high frequency and lower frequency as the cam lobe passes the sensor. The lower trace is a calculated frequency versus time graph which shows the clear drop in frequency from about 2500 HZ to less than 100 Hz. This, I believe is a signal similar to that which the DME uses to detect cam position with this type of sensor. My high frequency is about 2500 Hz not 100 kHz. I believe the measurement on your traces might be your digital oscilloscope sampling rate which would be orders of magnitude higher than your sine wave. My scope samples at 100 kHz. Not sure what the 120 kHz reference is to in the article. My sensor output signals are much smaller than yours but the sensor seems to be detecting the cam lobe. I will have to check into this. It may be that the amplitude is sensitive to distance of the sensor from the cam. Also note than my crank sensor signal was not taken simultaneously with my cam signal so the relative position of TDC to the cam signal (very important) cannot be determined from these traces. When I get back I will record them together to determine timing advance at different engine speeds. It is now possible that my sensor is working and the 065 error is being thrown due to an incorrect position of the cam at startup (stuck vanos?). But now knowing more about this sensor, I can start troubleshooting. I think what has been confusing on a number of forums is that the sensor is three wire and most assume that it must be Hall Effect even thought the electrical diagram shows that it is not.

1998 M Roadster Position Sensor Tracings.jpg

TSICK

[Adker]

Glad your having a good stay. Be glad you didn't have to deal with the Indy 500 traffic.

Your signals show the change in freq like I saw but your voltages are a lot smaller. My scope had the Ch 1 freq measurement turned on ,reported 102.9Khz, and the scopes sample rate was 125 Million samples per second. The scopes freq sweep rate was 2uSec per division and the sine wave repeats at around 10uSec =100KHz. I am not sure how accurate the DME freq has to be, it may be a simple tank circuit inside the DME so +/- 20% would be common. I did have luck measuring the freq with a DVM that can measure at that frequency. Measuring a 100Khz signal with a 100KHz sample rate is going to cause inaccurate readings. The scope should have 2x the sample rate of the measured signal (sampling theorem).

[tsick]

Hi Adker. I am back and have some updates. I found a scope that could sample at a higher frequency and you were correct. I have posted figures of the signals from Pins 1 and 2 and they are similar in amplitude and frequency to yours. Image 1 shows Pin 1 (upper) and Pin 2 (lower. There is a difference, however, in that my signals are 180 degrees out of phase. Will have to check my triggering settings to make sure this is real or not. The second image shows lower times scale of these 2 pins and a digital subtraction (middle). While I can see a change as the cam sprocket passes, I cannot see a frequency change as in your images. This may be due to the out of phase nature of my signals and that the subtraction is a function of the digital signals and not necessarily of the originals. I am thinking, however, that my sensor and DME are working OK, but still can't be sure. It is curious that my under sampled signals showed a clear frequency shift with rotation of the cam. As this was different instrumentation, I suspect I have a problem with the scope still. Will get back, but if you have any insight it would be greatly appreciated
IMG_1025.jpgIMG_1026.jpg

[Adker]

That is good news, it looks like the DME is generating the 100Khz sine wave so it may be OK. Since you know the sensor is the correct one, I would look at the trigger wheel to see if it is in good order. The distance to the trigger wheel from the sensor has to be right or you get all sorts of problems. To get a good scope picture of a low freq event on a high freq signal, you need a scope that has a large capture memory. You set the freq sweep rate low with a high sample rate. After the capture, you can zoom into any part of the capture waveform and see really good details of the signal.

I have seen a phase shift on a scope before where I wasn't expecting one. Some scopes sample ch 1 then ch 2 rather then both at the same time, that can cause the waveform to look out of phase. Look at the Horz trigger options in the menu.

[tsick]

Thanks for the advice. Not sure how much storage memory my scope has since it is old but I will play around with it today. I bought this car about a year ago after a texter rear ended my previous 1998 M Roadster. It was totaled but I found its exact twin (same year, arctic silver imola/black interior. I had rencently rcovred th leather seats and still had the hardtop so the new car got my new seats and I retro fitted the hardtop. Pretty much an even exchange with the insurance settlement and I sold my totaled car to Active Autowerke here about a mile from my house. Th seller mentioned something about replacing the VAnos, which I thought was odd as the car had only 62K miles. And the car seemed to run well. I had worked on almost every system on my old car so having another seemed like a goo idea. About two months ago I decided to scan the DME and found th 065 code but no check engine light. Checked the dash and found the socket for the light had been removed (my bad for not checking this but know now). Was hoping it was just a bad sensor and they (the owner/mechanic) couldn't get the light to go out so removed it. If I can confirm the DME and sensor are OK I will (reluctantly) take a look at the Vanos and cam timing. Possible that they did not install correctly and th timing is just off a tooth or so. Did the Vanos repair on my old car so it shouldn't take too long. Have the cam locking tools etc. Still not sure why my under sampled signal would give a nice frequency shift. Appeared that the sensor was at least seeing the wheel. Points to a measurement problem on my part as the sensor would have been using the high frequency DME signal even when I sample incorrectly. Thanks again

[tsick]

A quick follow up. Tested a known signal to both channels (either Pin 1 or Pin 2 from DME) and the signals were in phase. 180 degrees out of phase when compared to each other as above. With ignition on engine not running, both signals are steady at 103 KHz. With engine running, Pin 2 remains steady and pin 1 periodically shifts about 1/2 wavelength. I also made measurements with the sensor disconnected and to my surprise there is no high frequency signal from the DME ??? Apparently it needs to see the sensor.

Adker, just wanted to confirm that your DME is MS41.1 in case there may be a difference that would account for my phase shift. I have a spare new OEM sensor (VDO) so I think I will connect it to the circuit and see just how much proximity to a metal object affects the frequency shift. If it is significant, I will have to take of the valve cover and take a look.

[Adker]

My car is the same as yours with the same DME. The sensor has the inductor inside of it so it may be part of the oscillator tank circuit, just need to add a capacitor and operational amp (gain to sustain osculation, can be an inverting op amp) inside the DME and you have a oscillator. Try a measurement across pins 1 and 2 vs pin 1 or 2 to ground. It looks like the second trace is an inversion of the first one. I did see a little phase difference sometime, but if I moved the trigger point they lined up. A colpitt LC oscillator uses an inverting op amp to sustain the oscillation.

[Adker]

Have you ever ran across a schematic of the DME? Without schematic the DME has to be treated as a black box. It would be interesting to look at how they generate and detect the frequencies.There is a portion of this function that can not be tested external to the DME. the frequency shift detect circuit inside the DME. The only way to test this is the swap the DME with a know good one. From what I have read, the error returns as soon as you start the car and the PO disabled the CEL to hide the error. With that in mind, the DME swap looks like a good thing to do.

Maybe the two signals are inverted and my setup didn't see it. Bottom line, I would look at testing the sensor with a simulated trigger wheel and looking at the trigger wheel since you are getting the 100khz osc, then swap out the DME. If you are interested, an osc circuit that has a split indictor like what is inside the sensor. This osc has the 180 degree shift across the inductor relative the ground: https://www.electronics-tutorials.ws...r/hartley.html

[tsick]

I looked for the DME circuit diagram for a few days but could not find the MS41.1. It must be out there somewhere because the DME repair companies must use the circuit for their repairs. My scope does not actually store data but rather stores pixel position for the trace for each sweep. Then it allows digital subtraction of the two input signals to give a pseudo differential signal. When you slow down the sweep you lower the sample rate and then lose info from the high frequency waves. I am going to see a shop that does BMW Turbo and Supercharger installations as well as DME coding on Monday. The shop is Active Autowerke and is about 1/2 mile from my house. I am hoping they are familiar with the MS41.1 and can check its function. The past few days I have had 1) after clearing the fault code the car did not throw a code for about 2 days with 3-4 startups, then threw the code; 2) one day the CEL disappeared spontaneoulsy (must not have seen the code for a few startups) and ran for two days before it appeared again. A couple of time I have seen code 212 which is vanos mechanical sticking. It remains possible the my vanos in sticking in the wrong position (or previous owner had it changed and installed incorrectly) and the DME is throwing 065 when it sees the incorrect position at times. Hopefully will know Monday. But I have learned a lot about how this works which is why I tinker with this car a lot. Thanks for your continued help. Will update