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Thread: Golf 1.6tdi. Suspected G235 failure

  1. #1
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    Golf 1.6tdi. Suspected G235 failure

    Hello all,

    Long first post ahead, first I must apologize for not having a full Autoscan of my fault, this is because of a colossal moment of stupidity born out of frustration.

    My name is Alex and my car is a VW Golf 1.6tdi Variant CAYC engine and the fault is as follows. After diagnosing a faulty EGR assembly causing the car to cut out/not run at all I set about the enjoyable task of changing it on my driveway. After a few days work and multiple curses laid upon VW for the their placement of said assembly the swap was complete. The car started and ran straight away but on the test drive the flashing glow plug came on, defeat snatched from the jaws of victory.

    After returning and scanning I was getting a P5044 - Sensor 1 for exhaust bank 1 - Circuit Malfunction (apologies again, this is just the generic code I found after googling as I couldn't remember the VCDS code) which was cleared due to the aforementioned frustration assuming that I had left one of the EGT's unplugged, this was however not the case so I set about logging my 3 EGT temps. sensors 3(G495) & 4(G648) were showing sensible values following a short drive and with the engine running were slowly climbing, sensor 1 however is pegged at 19.98. Unplugging made no difference still pegged at 19.98 so I unplugged G648 for comparison and as expected when straight to 999.




    At this point I grabbed the wiring diagram from erwin.





    I measured the resistance across G648 and G235 as the plugs are right beside each other and found G648 to be 215 ohms with G235 at 7 Mohms, after a bit of quick googling I was very excited to see the location of G235 would possibly require me to strip off a good chunk of the parts I have just put back together following the EGR change to access it. Fantastic.

    I was still not convinced on the sensor being at fault due the temp showing at VCDS being stuck at 19.98 and was concerned there may be a car side wiring issue so set about a few more tests. First thing i did was plugged the sensor for G648 in (orange plug which requires a nub filing off to fit) into the G235 car side loom and my value changed to 693, nonsense but at least it was responding. I then dug out a couple of resistors and bridged the sensors to compare the results which I've quickly tabulated below

    ..............................G648.................G235
    Voltage @ ecu pin.....3.3V................3.29V
    100ohm resistor........-127...............872
    200ohm resistor........-1...................707
    sensor resistance......215 ohms..........7 Mohms

    This has led me to be 90% sure it is the G235 sensor which is dead, the only thing still confusing me is that the G235 seems to work the opposite way round to the G648. The G648 temp increases as the resistance does which I was expecting but the G235 decreases temperature as the resistance increases.

    My questions therefore are is this correct or is there still possibly a wiring fault on the car side? I having a suspicion that the reading for G235 may bottom out at 19.98 when open circuit but without a decade box I can't confirm this is the case. I'm struggling to see what wiring fault could cause this behavior and for the price of a sensor it's probably worth getting to plug in and check the response but if anyone knows the resistance value for a new G235 from a CAYC engine I would be very grateful before I pull the trigger on my order.

    Any help appreciated

    Thanks,
    Alex
    Last edited by alex760; 07-16-2020 at 11:12 AM. Reason: Test results formatting

  2. #2
    Benevolent Dictator Uwe's Avatar
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    Hi and welcome.

    You're gonna post a scan, right?

    -Uwe-
    Lock-down of sick people: Quarantine
    Lock-down of healthy people: Tyranny

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    Verified VCDS User iichel's Avatar
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    I'm doing surgery on a CAYB as we speak.

    What resistance would you like me to measure?
    Is it the black 6-pin, orange 2-pin, black 2-pin or red 2-pin?

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    Quote Originally Posted by iichel View Post
    I'm doing surgery on a CAYB as we speak.

    What resistance would you like me to measure?
    Is it the black 6-pin, orange 2-pin, black 2-pin or red 2-pin?
    The black 2-pin one would be fantastic iichel thanks!

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    Quote Originally Posted by Uwe View Post
    Hi and welcome.

    You're gonna post a scan, right?

    -Uwe-
    Hi Uwe, thanks for the welcome

    I was thinking perhaps I should go for a drive to recreate the fault so I would have a scan to share. I'm fairly sure that without sensor 1 working DPF regen will be inhibited though and it's nearly due for one so I am treading a little carefully.

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    Verified VCDS User iichel's Avatar
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    So at rest, engine cold, the sensor has infinite resistance on both the engine side and the sensor side.

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    Quote Originally Posted by iichel View Post
    So at rest, engine cold, the sensor has infinite resistance on both the engine side and the sensor side.
    Hmm thanks iichel, interesting perhaps my sensor is OK. If you get a chance to see what the sensors read on VCDS while cold I would be very grateful but no problem if not.

  11. #8
    Verified VCDS User iichel's Avatar
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    Well, the engine is currently divided into 500 separate parts, spread over my garage so it won't be easy doing so on short notice.

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    ah i see, nevermind thanks again for the help anyway.

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    For comparison, the engine was practically cold, it only worked for a few minutes:
    Address 01: Engine (03L 906 023 LG)
    7:24:53 p.m.
    IDE00025 Coolant temperature 39 C
    IDE00167 Exhaust temperature 1 bank 1 20.0 C
    IDE00169 Exhaust temperature 2 bank 1 20.0 C
    IDE02229-ENG102154 Exh.gas temp.sen 1-TEG_MES [0] 19.98 C
    IDE02234-ENG102117 Exh.gas temp.sen 3-TEG_MES [1] 53.85 C
    IDE02236-ENG102786 Exh.gas temp.sen 4-TEG_MES [2] 27.04 C
    IDE03270-ENG111636 Exh.gas temp.sen 1: unconditioned voltage-VP_TEG [0] 3.2861 V
    IDE03273-ENG111637 Exh.gas temp.sen 3: unconditioned voltage-VP_TEG [1] 0.6395 V
    IDE03275-ENG111638 Exh.gas temp.sen 4: unconditioned voltage-VP_TEG [2] 0.5962 V

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