Knock sensor low voltage - Page 2

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Thread: Knock sensor low voltage

  1. #31
    Neutral Maqcro's Avatar
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    So basically you want me to jumper G66 to G61 bonnet to see if I can get any voltage readings off the bank 2 sensor to determine if my ECM is actually bad?

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  3. #32
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    you know G66 works (cyls. 3&4) as get voltage variation....... as throttle is moved..... so if possible get a used G66 bonnet connector that plugs into the G66 and "gender" change it using some small bayonet (probably have to trim) connector to plug into the G61 wiring and actually could do same with the new G61 sensor you bought to also confirm it is good, gonna see if I can get pic from ECS web page to see what connector actually looks like

  4. #33
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    some place like an ACE hardware sells male and female "bayonet" style electrical connectors ,the most common has a 1/4" /.250" blade /tab width which you see everywhere on appliances ,but they make/have really small ones with .110 width you can trim down and get in the bonnet with a little fanagling and securely

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  6. #34
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    G61 is green G66 is blue. They are similar oval connectors just slotted differently so they can’t be connected wrong. I can maybe just trim that edge and maybe get the connector plugged in. I’ll work on something tomorrow morning and give an update.

  7. #35
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    the smallest male and female bayonet connectors will work....piece of wire, male on one end ,female on the other end ,that way you save a trip to the salvage yard

  8. #36
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    as a sidebar they both function the same ,however I believe they are "tuned" differently in the sense their harmonic frequencies are different

  9. #37
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    Modified the sensors to swap bonnets. Checked on voltage readings and I’m getting readings from G61 sensor and nothing from G66 now. All signs are now pointing to faulty ECM. Let me know what you think.
    Attached Images Attached Images

  10. #38
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    while system is "on"(where you are getting a good power reading to ECM from G61 sensor plugged into G66 bonnet) check for power at G61 bonnet, should have +12vdc at pin#2 across to pin#3( ground) if so, and you have/had good continuity from G61 bonnet pin #1 to ECM connection #106 pinout proven by the lamp bulb then itbwould confirm it isnthe ECM....ugh....really unusual

  11. #39
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    I’m getting my readings from vag tool block 26 but I can back probe G61 bonnet with G66 plugged into it.

  12. #40
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    leave G61 sensor plugged in to the G66 bonnet/loom ,take the G66 sensor out of G61 bonnet/loom and see what the voltage is with multimeter, should get a reading of +12vdc. with positive probe on #2 terminal on inside of bonnet and negative probe on #3 terminal on inside of bonnet

  13. #41
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    I’m not getting any voltage. Key on engine off and also tried with engine running.

  14. #42
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    check same terminals (#2&#3) on bonnet 66 with engine on and running..... should have voltage according to my post#21 diagram, D102 should have positive voltage and 220, does that make sense to you ? Just fighting myself not to believe ECM failure......

  15. #43
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    I think I already checked when I checked the last sensor but let me run out and again to be sure. Pretty sure I had no voltage on both.

  16. #44
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    Ok just as I remembered. No voltage on either bonnet on any pins in every variation of swapping sensors into opposite bonnet with engine running.

    Just for fun I checked resistance in the same scenario and I’m getting two different readings between the bonnets.

    G61; pin 1-2 125 ohms
    pin 1-3 125 ohms
    pin 2-3 .5 ohms

    G66; pin 1-2 1.0M ohms
    pin 1-3 1.0M ohms
    pin 2-3 1.3 ohms

  17. #45
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    with the G66 sensor out of engine, take your multimeter and check G66 bonnet with car running, do you have any voltage reading between terminal #2 and #3 ,according to wiring diagram 220 is a ground and D102 should have some sort of positive voltage

  18. #46
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    this might be better explained than I have done ,go to ; us.autologic.com/news/piezoelectric-knock-sensors .....the looms to G66 (cyl.3&4) and G61 (cyl. 1&2) each have 3 wires the # 1 wires in each loom go to the ECM the other two wires #2 & #3 in each are a reference voltage , ,multimeter readings per instructions i n above webpage should read some voltage and be the same as according to wiring diagram are connected, #2 should be positive like 5vdc. and #3 is ground, you could hook multimeter to #3 or ground on car

  19. #47
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    No voltage at all with sensor unplugged like I’ve been telling you 😂

    Tried with key on engine off and with engine running

    Tested G61 and G66 bonnets with both sensors unplugged

    Tested G61 bonnet with G66 sensor plugged into G66 bonnet

    Tested G61 bonnet with G61 sensor plugged into G66 bonnet

    Tested G66 bonnet with G61 sensor plugged into G61 bonnet

    Tested G66 bonnet with G66 sensor plugged into G61 bonnet

    So as you can see I’m getting no voltage in every scenario between pins #2 and #3 or any pins to be more specific since I tested all combinations.

    If I’m not getting voltage through those pins are we concluding the ECU is at fault here?

  20. #48
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    according to website with key on......engine off..... sensor unpluged you should get +5 volts DC on loom terminal #2 with loom terminal #3 attached to multimeter ground

  21. #49
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    Just read the website. Seems like I should be testing pin 2 and ground connection and pin 3 and ground connection. Not between pin 2 and 3?

  22. #50
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    From each pin I’m getting 0v connected directly to battery negative.

    From battery positive I’m getting full battery voltage to each pin except pin 1 on G66 I’m only getting 11v

  23. #51
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    Quote Originally Posted by Maqcro View Post
    Just read the website. Seems like I should be testing pin 2 and ground connection and pin 3 and ground connection. Not between pin 2 and 3?
    understand your frustration, forget the sensors themselves,they both are good, you have proven that, with the key on and engine off , referring to suggested website you should have reference voltage between loom pins #2 and #3 of approximately 5dc. volts if not refer to diagram in post #21................ circuit #220 is ground you should read 0 ohms between ground ,frame/engine,ground lug and loom pin #3. Pin #2 in loom should have voltage being fed by circuit #D102

  24. #52
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    the reason I say between #2 and #3 on loom bonnet is because this is what is connected to sensor ,if as an example #3 wire (which is the sensor ground) has failed (broken /cut) then sensor would not be able to have/get its reference voltage. To indeed see if #3 is a "good" ground you would check continuity between #3 loom/bonnet pin to ean engine,frame,etc.part and get a 0 ohm reading. As a caveat to all this it has occured to me that your G66 sensor could possibly be bad and is robbing voltage to the looms since #2 &#3 wires are common to both ,you I believe have a new sensor, a G61, , we will assume it is "perfect" /good ,with your multimeter check ohm reading between each one of the sensors 3 wires to the actual metal part of the sensor, now check G66 and see if it gives the same readings.

  25. #53
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    I’ve got a spare G66 laying around. I can check resistance between that and the one installed on the car and also G61

  26. #54
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    Ok checked sensors. All 3 are open on all 3 pins. I went ahead and replaced G66 anyways with my spare sensor and torqued to 20 nm. Same result, still have low voltage on G61.

    Btw what a pain changing G66 😵😵 extremely frustrating 30 mins 😂

  27. #55
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    it is possible that the G66, the one that appears "good" with the ECM has a short in it ,remote but possible........ I am going to check my Bentley tonight and try and trace #'s D102 and 220 , I know for sure that they should have a reference voltage across them.

  28. #56
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    It’s possible. I know what you mean. I should be seeing some kind of voltage. Unless the voltage is generated from the sensor itself. Engine vibration converted to a volt reading using the piezo sensor.

  29. #57
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    my understanding is this...... a reference voltage is set up and as vibration occurs the voltage is "modified" for lack of a better term through the piezoelectric crystal.....trying to help and am as frustrated as you are,will see what I can find in my Bentley.....

  30. #58
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    Ok let me know what to check on next. This car has put me through hell trying to fix it.

  31. #59
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    feel your pain brother ,what is puzzling is the fact that the G66 seems to work fine ......maybe even without a "reference" voltage it puts out enough when running to meet the ECM's threshhold...... the fact that you have two sensors in a parallel !!!! circuit is what is frustrating !!!!, should have at least a 5 volt reading at G66 bonnet pin #2 to get acceptable signal to ECM which you seem to be getting validated by VAGCOM .........looking like input to ECM from the G61 is not being recognized, hate to think it's the ECM until I see some sort of rational as to why no reference voltage at sensor loom bonnets

  32. #60
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    Well G61 is being recognized by vagcom but not like G66 is. G66 responds and fluctuates according to throttle position. As I push the gas and raise rpms the voltage from G66 rises.

    That’s not the case for G61. I need to hit around 2.5-3k rpms before I even get a change in voltage and it doesn’t change much at all, maybe raises up to 1.25v max where as G66 hits 10v+ nearing WOT.

    What if your right about voltage being stolen? But it’s being stolen by the engine speed sensor being that it’s partially on the same circuit?

    Just a thought, shoot the idea down if you don’t think it’s worth investigating.

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