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Thread: What's the purpose of the Center O2 sensor?

  1. #21
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    Actually, I should have rephrased my statement further ... in most of Ohio, and my county specifically ... they do no emissions testing or inspection at all for licensing. But I understand your point Jack ... legality.

    Also, I called the VW dealer today ... $110 to update the ECU firmware to the latest version. And all the recalls have already been done on this car.

  2. #22
    NostraJackAss Jack@European_Parts's Avatar
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    Actually, I should have rephrased my statement further ... in most of Ohio, and my county specifically ... they do no emissions testing or inspection at all for licensing. But I understand your point Jack ... legality.

    Also, I called the VW dealer today ... $110 to update the ECU firmware to the latest version. And all the recalls have already been done on this car.
    Correct just because a county doesn't test doesn't make it legal in Ohio or Federally.
    Thank you for capitulating.

    What campaign's were done?

    I'd sure like to argue that the update should of been done as part of an aforementioned campaign and as per the TSB or RTFB for free!
    European Parts Emporium/Performance / Immobilizer Solutions EPE
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  4. #23
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    OK, I've been driving the car to make sure it doesn't have any other issues before I sell it.

    When I first got the car, one of the faults was, "17746 - Camshaft Position Sensor (G40) P1338 - 001 - Open or Short to Plus - Intermittent". I just assumed it was one of the many faults due to the dead battery.

    After installing the new engine, I cleared the code, and it didn't return. A couple weeks later I did a scan and noticed it had returned ... hmmm ... this is a completely different engine, and completely different Cam Position Sensor. I replaced the Camshaft Position Sensor with the one off the old engine and cleared the codes again.

    In the last few days I noticed it had returned again, but now, with the engine running, if I cleared the code, it came right back. I figured it had to be a wiring harness issue. What's strange though ... the engine ran fine!?

    The other issue that I discovered is, the fuel pump doesn't run when the divers door is opened ... hence, the engine takes longer to start than normal after it's been sitting for a while. The interior light doesn't come on either when the driver's door is opened ... although the light DOES come on when any of the other three doors are opened. Obviously, I'll have to look at the driver's door latch. I mention this because I've heard longer cranking times can set a Cam Position Sensor code sometimes.

    I checked the three CPS terminals ... all where fine except term. 1 ... no continuity between the CPS connector, and the ECU plug terminal 98.

    So, after checking Bentley's wiring diagrams, I soldered a wire from Term. 1 on the CPS connector ... and made a three-way solder connection on term. 3 of the MAP Sensor connector (which is also connected to ECU Term. 98 - I had no codes for the MAP Sensor).

    After reassembling everything ... the car runs fine with no more codes ... and I drove it for quite a while.

    What I DON'T understand though is ... the engine ran fine BEFORE I fixed it! How could the engine even run WITHOUT a Cam Position Sensor?

  5. #24
    Benevolent Dictator Uwe's Avatar
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    Quote Originally Posted by Geoffzie View Post
    What I DON'T understand though is ... the engine ran fine BEFORE I fixed it! How could the engine even run WITHOUT a Cam Position Sensor?
    Crankshaft timing is really all that the ECU really needs for the engine to run. Particularly on older engines that don't have variable cam timing, the cam position sensor is primarily there as a means of rapidly determining the cam's phasing relative to the crankshaft. Think about it this way: When Cyl 1 is at TDC (as determined by the crank position sensor), it's either at the end of the compression stroke, or at the end of the exhaust stroke. With a functional cam position sensor, the ECU knows which of these is the case within one rotation of the crank (or less). Without a functional cam position sensor, it has to guess. It will figure it out eventually, but it may take a few rotations of the crank to do so. This means it may take a bit longer to "catch" when you're starting it, but once it does, the engine will run just fine.

    -Uwe-
    The engineering problems are likely insurmountable. It would be like proposing to land a rocket booster section on a barge floating in the middle of the ocean.

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  7. #25
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    Then that may be an additional reason why it takes a few cranks to start. Although I had a fuel pressure gauge on it overnight, and the pressure does drop to zero over time.

    I do believe this engine has variable valve timing on the intake cam at least ... the 2005 engine that I took apart had it.

  8. #26
    NostraJackAss Jack@European_Parts's Avatar
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    OK, I've been driving the car to make sure it doesn't have any other issues before I sell it.

    When I first got the car, one of the faults was, "17746 - Camshaft Position Sensor (G40) P1338 - 001 - Open or Short to Plus - Intermittent". I just assumed it was one of the many faults due to the dead battery.

    After installing the new engine, I cleared the code, and it didn't return. A couple weeks later I did a scan and noticed it had returned ... hmmm ... this is a completely different engine, and completely different Cam Position Sensor. I replaced the Camshaft Position Sensor with the one off the old engine and cleared the codes again.

    In the last few days I noticed it had returned again, but now, with the engine running, if I cleared the code, it came right back. I figured it had to be a wiring harness issue. What's strange though ... the engine ran fine!?

    The other issue that I discovered is, the fuel pump doesn't run when the divers door is opened ... hence, the engine takes longer to start than normal after it's been sitting for a while. The interior light doesn't come on either when the driver's door is opened ... although the light DOES come on when any of the other three doors are opened. Obviously, I'll have to look at the driver's door latch. I mention this because I've heard longer cranking times can set a Cam Position Sensor code sometimes.

    I checked the three CPS terminals ... all where fine except term. 1 ... no continuity between the CPS connector, and the ECU plug terminal 98.

    So, after checking Bentley's wiring diagrams, I soldered a wire from Term. 1 on the CPS connector ... and made a three-way solder connection on term. 3 of the MAP Sensor connector (which is also connected to ECU Term. 98 - I had no codes for the MAP Sensor).

    After reassembling everything ... the car runs fine with no more codes ... and I drove it for quite a while.

    What I DON'T understand though is ... the engine ran fine BEFORE I fixed it! How could the engine even run WITHOUT a Cam Position Sensor?

    Crankshaft timing is really all that the ECU really needs for the engine to run. Particularly on older engines that don't have variable cam timing, the cam position sensor is primarily there as a means of rapidly determining the cam's phasing relative to the crankshaft. Think about it this way: When Cyl 1 is at TDC (as determined by the crank position sensor), it's either at the end of the compression stroke, or at the end of the exhaust stroke. With a functional cam position sensor, the ECU knows which of these is the case within one rotation of the crank (or less). Without a functional cam position sensor, it has to guess. It will figure it out eventually, but it may take a few rotations of the crank to do so. This means it may take a bit longer to "catch" when you're starting it, but once it does, the engine will run just fine.

    -Uwe-



    Some engines won't run without a valid cam sensor input, all depends on programming and if it isn't present, it won't run fine, it will run with a reduced output map & with maybe even a lower top RPM or TQ request value.

    The issue is in the harness and a common problem for shared track components can be observed in the WD.

    An isolated overlay from ECU to G40 directly, will correct the condition..........

    Observe the WD and you will see........

    NostraJackAss Has Spoken!
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  9. #27
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    Yes, I know Bentley's shows that the G40 (CMP), G71 (MAP), and G28 (CPS) all share a common connection at D101 (in the engine wiring harness) then back to term. 98 at the ECU. Since the G71 and G28 had no fault codes and were working fine, I figured the break had to be between the G40 and D101.

    Apparently, engine wiring harness shorts are a common problem in Mk5's.

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  11. #28
    NostraJackAss Jack@European_Parts's Avatar
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    Yup..........the chemical bond connections are for shit.
    European Parts Emporium/Performance / Immobilizer Solutions EPE
    Certified Master Trained ASE/SAE/NASTF Legal Factory Authorized/Licensed GeKo/FaZit # 403738
    Specializing in Custom Services IE: "welding-fabrication" / EPA-SMOG Update or Pass-Thru-Programming / Data Transfer / Immobilizers & OEM Quality Parts

    www.FixMyEuro.com <<<<<CLICK HERE! or vwemporium@aol.com ( JPPSG & Unverified members need not PM me & Please don't email for free tech support...use the forum )
    Getting you CONTROL again of your property - TAKE IT! In Conjunction with.........

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