2001 Passat Knock sensor code comes back

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Thread: 2001 Passat Knock sensor code comes back

  1. #1
    Neutral Maqcro's Avatar
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    2001 Passat Knock sensor code comes back

    Hey guys I’m a new vw owner and I’ve been running into this code that keeps coming back.

    I’ve got a 2001 Passat 1.8l AWM automatic

    Here are the codes:

    P0327 - knock sensor 1 circuit low input

    16711 - knock sensor circuit low bank 1 - no indication on display

    16795 - secondary air injection reaction injection system incorrect flow detected - no indication on display

    16808 - bank 1 catalytic converter system not efficient enough - no indication on display

    The car seems to idle just fine but has really bad acceleration. Pedal to the floor and it barely wants to speed up at all.

    I’m assuming the knock sensor is preventing engine damage sense it can’t read a proper signal?

    I’ve already tried replacing the bank 1 sensor ( the green one ) torqued it to 15 ft/lbs and nothing changed. Still bad acceleration and code came back.

    Did I torque it wrong? Bad connector on wiring harness? Is there a fuse somewhere? What is the proper way to troubleshoot this... also I don’t have a VAGcom thing I’ve been reading about.

    Thanks.

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  3. #2
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    were the ohm readings the same on the old one as the one you replaced ? Knock sensor is an "input" to ECM as to timing(retarding and advancing), when it senses "pinging" it results in cam tensioner adjusting accordingly.......so I am told.......how are you retriving codes? If you have laptop consider cable and Ross-Tech lite

  4. #3
    Neutral Maqcro's Avatar
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    I never ohmed out the knock sensors. I scanned for codes using Bosch advanced obd2 scanner. It came up with knock sensor code and I replaced the sensor since it was fairly cheap. I still have the old sensor and I have a fluke multimeter. What pins should I be looking for resistance on and how much? I’m assuming I can only ohm out a knock sensor while the car is running.

    I do have a laptop... what would I need just a usb to obd2 connector and some software for Ross to work?

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  6. #4
    Neutral Maqcro's Avatar
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    I’ve ordered a cable to use with my laptop. Should arrive in 3-5 days. In the meantime I can ohm out knock sensors. What about checking for voltage. If the sensor had no power then it wouldn’t be sending a signal?

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    not sure but there are two basic functioning style of sensors some have 3 wires, some 2 wires regardless use new one to compare to old one. , believe the knock sensors have just 2, it sends a very small "signal" to ECM,resistence should be same ,if you can find a "pinout" diagram for the two wires that go to ECM (I will look for one tonight) you can check continuity between ECM plug and the corresponding knock sensor wires for "breaks" ,if indeed it is knock sensor problem I would be more suspect of wiring than sensor

  8. #6
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    it generates its own power using a piezoelectric crystal tuned to the engines frequency

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    Except that a knock sensor isn't powered externally. It's a piezoelectric microphone - vibration causes it to generate voltage. The ECU looks for specific frequencies and amplitudes in that output to detect 'knock.'
    If absolutely no signal is 'heard' after engine start (because there's always some noise), then the sensor is deemed 'faulty.' And, for failsafe measure, no knock sensor input = no ignition advance (which equals "I'm driving a 1980 Rabbit diesel" acceleration. )

    Check the wiring between the knock sensor & ECU.
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  10. #8
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    Sure so the ks is just a transducer converting vibration into electrical signal.

    I’ll check the wires from harness to ECM tomorrow morning. ( I work overnights 😵😵 )

    Just checking the ECM is in the box on driver side with the 5 bolts under the cowl to the right of the brake booster? should I be unplugging the battery and then unplugging the harness from the ECM before checking for continuity so I dont potentially damage the ECM?

  11. #9
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    My sensor has 3 wires labeled 1 2 3

  12. #10
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    I'd guess one wire is a ground shield and the other 2 wires are signal (+ and ground). I'd also guess the resistance of the piezo element would be quite high since it is a voltage driven (or generating) device.

    It probably isn't something that can be tested with a multi-meter but there's nothing to lose by trying.

  13. #11
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    I’m with you on that. Probably high resistance... 100k+

    Any info always helps. I’ll be working on getting to the ECM tomorrow afternoon.

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    Per the Bentley manual:

    The resistance between any two terminals of the knock sensor should be infinity (open circuit). (Measured with wire harness unplugged.)

    The knock sensors have three wires:
    > Pin 1: signal to ECM: white, ECM pin 106 (sensor 1), yellow, ECM pin 107 (sensor 2)
    > Pin 2: common to both sensors, to ECM: brown (sensor 1), green (sensor 2), spliced in harness, ECM pin 99 (brown)
    > Pin 3: shield, black. Spliced in harness to signal ground, connects to ECM pin 108

    You could easily check the wiring for pins 2 & 3 by confirming continuity between the same pin of knock sensor 2.

    I've not heard of many knock sensor problems, so check the harness for damage. The "low input" code could be caused by a ground on the signal wire, or an open circuit (broken pin 1 wire).
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  15. #13
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    So I was able to get into the ECM and measure continuity between the ks connector and ECM connector.

    .3 ohm on pin 106
    .3 ohm on pin 108
    .3 ohm on pin 99

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    How would I measure between pin 2 and 3? Measure pin 2 between sensor 1 and 2?

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    Since you opened the ECM and measured the wire continuity, there's no need to measure between the two sensors. (The Pin 2 wires for both knock sensors are spliced in the harness, likewise Pin 3 wires. Thus you could check the Pin 2 wiring, for example, by checking for continuity between Pin 2 of the two sensor connectors.)

    So, you have continuity for all three wires. That doesn't leave much to check, except to verify there's not a short between Pin 1 and ground (which there shouldn't be).

    This is a puzzling problem.

  18. #16
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    Yes very confused on this one which is why I’m here looking for guidance from the experts 😁

    How can I check for short in wiring? Check for continuity between pin 1 from ks connector to common ( pin 99 ) on ECM..?

  19. #17
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    With both sensors and the ECU unplugged.
    Measure the resistance between ECM plug pins 106 & 99, 107 & 99, 108 & 99, 106 & 107, 106 & 108, 107 & 108.
    And between ground and 106, 107, 108, and 99.
    All should read infinity (Open circuit)

    If your other measurements were correct and all of these are infinity, it would appear that you have a faulty UCU.

    "So I was able to get into the ECM and measure continuity between the ks connector and ECM connector.

    .3 ohm on pin 106
    .3 ohm on pin 108
    .3 ohm on pin 99"
    I suggest you do this check to the other sensor connector.
    Last edited by Tomvw; 04-28-2019 at 11:57 AM.
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  20. #18
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    I’m assuming if I get any continuity between any of these connectors I will have a short in the harness. If all are open (which they should be) I have a bad ECM... I’ll be checking into this sometime tomorrow and will give an update.

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    not to be daft...... I know there is one knock sensor on my 1.8 on block under intake manifold ,where is the other one located?

  22. #20
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    They are both under the intake manifold. One between cylinders 1 and 2 next to thermostat housing. One between cylinders 3 and 4. Sensor 1 is green sensor 2 is blue and they connect under the coolant reservoir.

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    you da man, thanks!!! makes sense the more I think about it

  24. #22
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    I’ve tested all points you mentioned and all are open readings. I’m wondering if maybe the connector isn’t seating 100%???

  25. #23
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    You see how the tab is broken on the green connector.
    Attached Images Attached Images

  26. #24
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    Bump

  27. #25
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    Have you done the continuity test on the other connector ?

    If there is a bad connection in any of the relevant connectors, that would cause a problem.

    That broken part is to keep the plug seated, if the plug is fully seated, that is not causing a problem.
    If there is no fault in any of the connectors, wiring or sensors, the fault must be in the ECM.
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  28. #26
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    I haven’t checked sensor 2 (blue) but I can do that tomorrow morning.

  29. #27
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    in this thread there is multiple references to the ECU connector "pin outs" out of curiosity and future reference where is this info archived ,here in forum info base,Bentley, or internet site ? , I have a suspect wire (intake temp) and while car is in garage could check

  30. #28
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    Bentley has it from what I remember. I think there were very small numbers on the either the ECU or plug too.

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    thanks Tex !

  32. #30
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    Quote Originally Posted by cchief22 View Post
    in this thread there is multiple references to the ECU connector "pin outs" ...
    The Bentley schematics are the only source I know of, and you have to select the correct schematic for your model year and engine.

    There isn't a specific pin listing for the ECM connector, rather you just have to go through the schematic and find the individual connector pins. But the schematics are organized by device, so finding the wiring for the intake air sensor (or what have you) is pretty easy.

    There a few devices--the Climatronic head unit, for instance--that do have pinout lists in Bentley, but not the ECM. If you went through all the ECM schematics, you'd find that a particular pin is always an input, or an output, or some specialized function. It's likely that all the ECMs are the same circuit board, but with different functionality programmed per the loaded program.
    cchief22 likes this.

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