Cylinder 1 Misfire - 1999 1.8T Passat
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  1. #1
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    Cylinder 1 Misfire - 1999 1.8T Passat

    This one has me stumped. 109k on 1999 1.8T Passat, only had to replace battery and alternator 3 weeks ago in the 1.5 yrs we have owned it. While my wife was driving in town she "went around a corner" and the car started running very poorly. Ran an OBDII scan when I got home and found a P0301 (misfire on cylinder # 1) misfire on waiting for me.
    I have tried to ring out the problem the best that I can to no avail. I have put in new plugs... still P0301. I have swapped coils with other cylinders... still P0301. There is battery voltage (12.45V) and a ground at the #1 coil harness connector; also a flashing LED test light indicates fire signal to the coil. The #1 fuel injector is getting a fire signal as well, and I even went so far as to replace the #1 injector as well (dropped and broke when I was attempting a swap). I have attempted to check the ICM, but am unsure how exactly to tell if it is good or bad. When reading from pin 3 on 5 pin side to all the sucessive pins on the 4 pin side, ohm-meter shows .45 mOhm across 3 of the terminals and 1 Ohm (no connection) on the pin nearest the cab. Does this sound like the ICM? Does anyone know which ICM pin (on the 4 pin side) correlates to cylinder #1? Are non Bosch brands sufficient, or should I stick with OEM for the ICM?
    Any and all help is greatly appreciated.
    Thanks!

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  3. #2
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    It sounds like the ICM to me. But usually you get a flashing CEL.

  4. #3
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    It does have a flashing CEL (forgot to mention that).
    Is there a diagram that shows which pin on the ICM is for which cylinder... this would be the icing on the cake for diagnosing the ICM as bad.
    Cheers

  5. #4
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    With your years and mileage, I wouldn't bother with any further troublehsooting, especially since you've eliminated the coilpack - it is assuredly the ICM.

    I don't know which pins are which - IIRC there's an Info Forum writeup(?).

    The Bosch ICMs are the ones that are systemically bad. The Huco ICMs have an occasional failure. You can get the Huco for $100-$120 a lot of places. One place with free (ground) shipping is www.autohausaz.com.

  6. #5
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    I recommend autohausaz as well. I actually drive down to their location and pick parts up at will call.

    Anyway, sounds like an ICM to me as well.

    On the input side (4-pin side) the pin numbers correlate with the cylinder number. On the outputs, the middle of the five pins is ground. The rest of the four correlate with the input pins. Either way, it is typically a bond wire in the ICM that fails. In my case it was a bond wire that failed between the #2 cyl transistor and the output pin of the ICM. My #2 cylinder output resistance measurement was different than the other three.

    You can perform three different sets of measurements...
    1) Each of the 4 inputs to ground (pin3 on output side?)
    2) The other 4 outputs to ground (yada yada)
    3) Input to output

    If any of the four measurements are different than the other three, it is highly likely that the ICM is bad. I actually fixed my ICM to use as a spare when my new one fails. I'm currently on my 3rd ICM at 119k miles.

    It is a failure prone part. Sounds like you've been very fortunate with car repairs until now.

    -Mark

  7. #6
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    Forgot to add that it is quite possible that the bad connection in the ICM is able to supply enough current to drive your LED test light. So, you've proven that there is "A" signal getting to the coil, but it is likely that the ICM cannot supply the amount of current the spark plug needs.

    My guess is that your ICM is bad, you've proven that the connection isn't completely "open" with the test light, but the connection is really bad, or about to fail completely, causing a flashing CEL and misfires on cyl 1.

    -Mark

  8. #7
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    I ran into this problem last summer when I went home on leave, and yep...the ICM was the culprit. Next day delivered the Hugo one for like 115-120 bucks.

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    Thanks for all the good info!
    I have a Huco ICM on the way ($105), also replacing the plug boots ($6 each), as Autohausaz.com mentioned that a faulty boot can cause failure of the ICM. The ICM has to be the easiest part I have ever removed (including wiper blades!)
    Will let you know how it turns out.
    Last edited by amhennes; 08-04-2006 at 01:44 PM.

  10. #9
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    Quote Originally Posted by amhennes
    ...also replacing the plug boots ($6 each), as Autohausaz.com mentioned that a faulty boot can cause failure of the ECM...
    First I've ever heard of this.

  11. #10
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    Quote Originally Posted by Rusty
    First I've ever heard of this.
    I'm pretty sure ICM failures are from crappy ICMs.

  12. #11
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    The bad extender (boot) can cause misfires on that cylinder but if you swapped coil packs around AND swapped the plugs, then you would have almost assuredly noticed a cracked extender so I doubt this is the issue. But at $6 each, I guess it can't hurt to swap them on a car with your age and mileage.

  13. #12
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    Wonder if the extenders could be contributing to my twitchy idle (like 50 rpm blips)

    -Mark

  14. #13
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    ECM (brain of the car) != ICM (Ignition control module)

    I can see how a bad boot connection could affect current delivery from the ICM. It would seem to me like a bad connection (higher impedance) in the extender would cause the ICM to decrease its output on that cylinder. Granted, it has an effect, but I don't think a bad extender could cause premature ICM failure, unless there is arcing, etc, at the extender. The biggest worry is a reduction in current to the plugs that causes misfires and the notorious blinking CEL.

  15. #14
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    Sure enough it was the ICM. Replaced the faulty Bosch with a Huco from Autohausaz.com for $105 and she purs like a kitten and no more CEL of any kind. Also replaced the plug boots (although mine didn't look bad at all... now I have spares) and tossed in some new plugs while I was there.

    Thanks all for the help and confidence in diagnossing the ICM! When I tested the across the pins on the broken ICM, it was obvious that the pin labled #1 (on 4 pin side, corresponding to cylinder #1) had a different resistance (between #3 pin aka ground pin on the 5 pin side) from the #2, #3, and #4 pins. For control the new ICM had the same resistance between all 4 pins.

    Now on to other things I have been putting off... timing belt job and abs module rebuild...

  16. #15
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    Great to hear! Congrats on the fix.

    -Mark

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    I had gotten ICM (had no brand name on ICM or the box, had no thermal sink) from autohausaz.com last year and it worked well only for 2-3 months. I got a replacement one and this time it was Huco. The contents were better packed this time. The ICM lasted about 8-9 months and then started giving problems. Few times, the car died while backing up. I had to put the bad OEM ICM to start the car and then replace the Huco back in and it worked normal again.
    now, I have started getting Cylinder misfire consistently. I am requesting for a refund.
    Their service is good, but I felt the quality of the parts is really poor. The coilpacks I got from them is poor quality rubber and while pulling them out, most of the time the head will separate from rubber part.
    I am looking for alternate places to buy a reliable ICM.

  18. #17
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    Did you use the heatsink paste?

    Do you have the plastic cover over the ICM? That airbox cover blocks a lot of engine heat from the ICM, if you don't have it the ICM may be getting too hot.

  19. #18
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    Based upon all the ICM issues with the AEB I decided to buy one for a rainy day. I've had a few rare instances of failure to cold start, and idle stumbling/hunting while very hot this summer (no codes), and since my ICM is 8 yrs old, prob should be prepared. Decided the Huco unit seemed to have "issues" and wanted to replace with stock Bosch (which also has "issues"). Best price I could find was Getcoolparts.com, $138 brand new/free shipping.

  20. #19
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    I just replaced my ICM due to the same issue.

    '99 1.8T Pasat Wagon 75,xxxK

    Whoo-hoo!

  21. #20
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    If I had bought a spare ICM at 96K miles, it would have saved a day of vacation. Instead my wife ran around trying to find one (dealership, $420). I was already out of town with the kids, and she had to do the install.

    If I had bought one in advance and installed it in advance, we could have avoided the whole adventure, including losing the spring clip from the connector (we think it landed on her shirt, and we later found it in the trunk).

    It did make a great story.

  22. #21
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    Quote Originally Posted by Rusty View Post
    Did you use the heatsink paste?

    Do you have the plastic cover over the ICM? That airbox cover blocks a lot of engine heat from the ICM, if you don't have it the ICM may be getting too hot.
    Yes, the plastic cover is there and everytime, I have to experiment, I will add heatsink. Ordered another Bosch ICM from autohausaz.com. The box does not have any screws, or heatsink paste. I would imagine the box would have something which would mention part no, manufacturer etc. Or may be I am naive about auto parts industry.

  23. #22
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    Quote Originally Posted by mghunt View Post
    If any of the four measurements are different than the other three, it is highly likely that the ICM is bad. I actually fixed my ICM to use as a spare when my new one fails. I'm currently on my 3rd ICM at 119k miles.
    This post is old, but I was hoping you could tell me how you managed that. This looks like a solid piece of plastic to me. I have a Bosch one with an open resistance on one pin. Is it the front that comes off? Oh well--I have one coming overnight.

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