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-   -   Low Reference Voltage on Exhaust CPS Harness (http://forum.e46fanatics.com/showthread.php?t=923595)

Dz1087 05-23-2012 07:01 PM

Low Reference Voltage on Exhaust CPS Harness
 
All,

I just purchased my first BMW a week and a half ago. Although I'm very excited about driving it, the SES came on with P0369 as the code. I had it cleared, then the next day it threw P0369 and P0344 and was stalling from stop signs and lights like others have described WRT CPS problems. Well, I replaced the exhaust CPS first, thinkig it may have tripped the intake. The day after I replaced the exhaust side, the 0344 code came up again. I had it cleared yet again, and now the 0369 code is back.

Anyway, I just finished watching the Bently YouTube of checking the CPS. I went out to check my harness first, as in the video, and my reference voltage, which should be 5.00 per the video was only 2.53.

Now, I had a probe touching the ground part of the plug, and the center and it gave me 2.53. Touching the supply voltage side, I got 12.34 == bat. So, unless I am missing something, it appears that the voltage running to the sensor itself is off.

I am hoping some of you fanatics have a few words of wisdom on this problem.

I'd also like to go ahead and thank everyone for the content on this site, it has been really helpful so far with my purchase.

dmax 05-23-2012 08:20 PM

Did you try just cleaning the connections with electric cleaner? The SAP valve gasket on mine was seeping oil and I think it got all over that connection.

Also, if you didn't know, our cars are finicky about only liking OE sensors/electronics. If AM sensor, that itself could be the issue.

Dz1087 05-24-2012 12:56 PM

The voltage is from the wiring harness itself, with it disconnected from the sensor and the ignition in the on position. The Bentley video said reference voltage should be about 5v from that harness. I only had about 2.5.

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Dz1087 05-25-2012 08:02 AM

So, nobody has any ideas on this? I'm going to be testing it again today with the sensor to see if it hits 0 volts when metal is near the sensor head.

Dz1087 05-25-2012 10:06 AM

So, I tested the old sensor and it tested good, assuming that going from 2.72 to 0 volts indicates a good test since I don't have 5 volts coming from the vehicle.

This is the video I mentioned earlier.

http://www.youtube.com/watch?v=jUZAiHpuF0s

zaharias 06-20-2012 09:21 AM

Did you fix your problem..??

Dz1087 09-08-2012 01:35 PM

Well, I replaced both sensors after my inspection II came out with the same conclusion that it was just the sensors. It no longer has the codes, but still hesitates when accelerating. It hasn't completely stalled out on me since, though.

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jfoj 09-08-2012 02:15 PM

Not sure however most of the sensors have a 5 Volt reference from the DME.

You need to see where the Voltage drop is, either the wire is partially grounded or there is a problem with the connections or reference from the DME.

If you can backtrack the wire to the DME you can unplug the harness and see if the reference goes to 5 Volts. Also you should compare if the other CPS had 5 Volts as well.

If you do not have issues with the CPS or the reference, check the 2nd link below in my signature for more info on fuel pump problems that cause driveability issues.

Dz1087 09-08-2012 05:59 PM

I may test it again later today. The tech at the dealership said he thought it was in some sort of safe mode since i was testing it with the SEL on.

Dz1087 09-09-2012 08:41 PM

Quote:

Originally Posted by jfoj (Post 14715545)
Not sure however most of the sensors have a 5 Volt reference from the DME.

You need to see where the Voltage drop is, either the wire is partially grounded or there is a problem with the connections or reference from the DME.

If you can backtrack the wire to the DME you can unplug the harness and see if the reference goes to 5 Volts. Also you should compare if the other CPS had 5 Volts as well.

If you do not have issues with the CPS or the reference, check the 2nd link below in my signature for more info on fuel pump problems that cause driveability issues.

So, I haven't checked the voltage yet, but does the fuel pump cause a delayed start like I described?

I'm thinking maybe a DME update s due after reading a few threads on this forum here. Gonna go out and check the voltage though, right now.

Dz1087 09-09-2012 09:32 PM

OK.....

Just got done testing the exhaust sensor again. Turns out I'm still at 2.27V at the sensor.


I'm gonna tear into the wiring tomorrow to see if the DME is actually outputting 5V.

My biggest question is now, then, if the DME is NOT outputting 5V to the sensor lead what does that mean???? Am I going to be able to have the DME updated and it cures this, am I going to be ab;e to reset all adaptations and it cures this????? Has anyone had this problem - not enough volts going to the sensor????


And since he stopped by for a visit ----- JFOJ ----- Does your fuel pump thread account for low voltage at the exhaust CPS? I haven't yet tore through the wiring for this matter. Hopefully I will be able to get through the wiring this week, but what may I be incurring to fix this problem? Should I change the fuel pump over having the DME updated/adapts reset?? or should I have the Adapts reset/DME updated and the then see if I have enough change for a fuel pump.

jfoj 09-10-2012 05:48 AM

DZ,

Almost all computer controlled cars use a 5 Volt reference to things like cam, crank and throttle position sensors.

I have not measured a "known good" E46 camshaft sensor connector, however, I have reason to believe you should have 5 Volts, or very close to it at a disconnected camshaft position sensor connector.

Low Voltage means too much Voltage drop or a partially grounded wiring harness (bad or corroded connection or possibly a bad solder joint in the DME where the connector pin meets the main board). Worst case you may have a more severe problem requiring the DME to be replaced, which I would suspect would be a worse case situation.

Flashing the DMW will not cure a low sensor supply or reference Voltage. Also adaptations are always moving and resetting themselves. If you manually reset them, you just force them back to baseline to start from a default, usually speeding the process up a bit if you make changes to the engine.

I would check the reference Voltage to the other camshaft position sensor if you can easily disconnect the connector. Then I would check the reference Voltage directly at the DME with the sensor and the harness disconnected, then connect just the harness with the sensor still disconnected and see what values you measure.

Check the the pins in the harness at the DME are clean and tight when you have the harness disconnected.

You should be able to figure out quickly if the problem is the DME, harness or connectors.

jfoj 09-10-2012 06:18 AM

One thing to understand is crank and cam sensors are usually Hall Effect sensors and do not rely on the reference Voltage being dead on as much as something like an analog sensor like a throttle position sensor.

That being said low reference Voltage could cause a sloppy waveform from the sensor and translate to performance problems. If the reference is low it will likely cause something to play incorrectly.

Dz1087 09-10-2012 09:26 PM

Thanks, jfoj. I'll tear into the wiring harness tomorrow and see where it goes.

jfoj 09-10-2012 09:54 PM

Do not make it any harder than you need to.

Figure out what wires are are for the camshaft position sensor and pay only attention to them at the DME.

This link below should be your best friend.

http://wds.spaghetticoder.org/en/e46/

Dz1087 09-16-2012 09:32 PM

Thanks for the link, although it will take me a while to pour through all that.

I did check the other sensor today though, and guess what? 2.73 volts! Same as the other.

Could this perhaps be a fuel pump problem? Anything but the computer?

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Dz1087 09-18-2012 06:56 PM

Quote:

Originally Posted by jfoj (Post 14721119)
Do not make it any harder than you need to.

Figure out what wires are are for the camshaft position sensor and pay only attention to them at the DME.

This link below should be your best friend.

http://wds.spaghetticoder.org/en/e46/

Jfoj, do you think that this could be a fuel pump issue? Haven't had time to pour through the dme yet, but I just read your fuel pump failure thread and it mentioned hesitation as some of the symptoms of a soft fail.

Just thinking.

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jfoj 09-18-2012 07:40 PM

Here is my theory, if you think your fuel pump/filter is giving you problems, for the $125-$160 you should probably replace the pump & filter.

Even if it does not resolve your issue, you have eliminated a typical failure point in the car and can then focus on other issues. The pumps soft fail and many people are surprise on the improved performance with a new fuel pump.

Also make sure your fuel pressure regulator vacuum lines are in good shape, both under the car and at the F connector on the upper intake elbow.

DISA, VANOS seals and MAF can also cause issue, however, the fuel pump is probably the cheapest and easiest thing to rule out. VANOS seals are not expensive, but add the valve cover gasket and the time to do the work, it is the most complex repair out of the 4.

DISA is an easy check and is about $175 for a replacement. MAF is close to $200 depending on which one.

The car is 9 years old, it is worth refreshing sensors as they do not last for ever, but a refresh is probably much cheaper than a new car and if you can DIY, most of these tasks are not too difficult.

Dz1087 09-18-2012 09:04 PM

Honestly, at this point, I think I may sell the car depending on the outcome of the dme test when I tear into that. I bought it thinking it would be less of a maintenance hog than my 1999 Cherokee. I'm finding that may definitely not be the case.

It certainly drives better, though.

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jfoj 09-18-2012 09:10 PM

13 year old car, what do you expect.

You really need to refresh most of basics.

Short list
Most underhood rubber parts
O2 sensors
Camshaft position sensors
CCV
Cooling sytem
Lower control arm bushings
Fuel pump & filter
DISA

I probably left out a few things, but these are pretty common items that you should expect in almost any 13 year old car.

But you need to make sure your subframe is in good shape before you commit to the car, otherwise you may be in for a surprise


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