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    Thread: no start condition, no ecu communication?

    1. Member dudeman08's Avatar
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      04-15-2011 08:33 PM #1
      as you have already read in the title, my car wont start. 1998 jetta mk3 2.0 5spd. when i put the key in the on posistion, i dont get the check engine light like youre supposed to. the bulb didnt burn out, i know this for a fact and it come back on ever once in a thousand tries. whenever the CEL isnt on it wont start and whenever it is on it will start. sometimes when it does start it runs rough, others its pretty normal. i tried to put my scanner on it when the CEL was out but it kept coming up with a comm error and when it is on, i get no sort of codes or anything. any ideas? it didnt start happening untill i started banging out my sound deadener from the floor and under the dash. i cleaned my battery posts and cables and the ground to the trans and starter connections. startin to get frustrated. any help would be nice. thanks in advance.

    2. Member greyhare's Avatar
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      04-15-2011 09:59 PM #2
      Check relay #3. It should have a 30, 109, or 288 on it.

      Relays are numbered as follows:

      19 20 21 22 23 24
      13 14 15 16 17 18
      1 2 3 4 5 6
      7 8 9 10 11 12
      >

    3. Member dudeman08's Avatar
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      04-15-2011 10:02 PM #3
      what is it id be looking for?

    4. Member dudeman08's Avatar
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      04-15-2011 10:06 PM #4
      you know what, i do remember bumping my arm up against the fuse block and other things under there. ill check to make sure its seated properly tomorrow. ill let ya know whats what. thanks.

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      04-15-2011 10:11 PM #5
      Pull it out and plug it back in. It's the ECM power relay. You should hear/feel it click

    6. Member dudeman08's Avatar
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      04-15-2011 10:19 PM #6
      yo, weird as hell. i just checked and i dont thave that relay. just for s&g, i put the key in the on posistion and the CEL came back on. wtf? what should i do? i know this will keep happening.

    7. Member dudeman08's Avatar
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      04-15-2011 10:41 PM #7
      lookin around on different parts sites, the only cars that use it are up to mid 1996. i guess mine is spposed to be like that? what other possible cause for this?

    8. Member greyhare's Avatar
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      04-16-2011 11:44 AM #8
      Based on your original post; you knocked something loose while removing the sound insulation.

      Get under the dash and check for loose electrical connectors.

    9. Member dudeman08's Avatar
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      04-18-2011 04:39 PM #9
      any possible ideas what it could be? i was using a hammer and a chisel to break up the tar sound deadener from the floor and uner the dash. could the vibration alone have caused something to happen? i think i lost a ground somewhere, just not surewhat to or what not. im about to take everything out of the fuse/relay block and plug them back in one by one to see if that helps. i even unplugged and reconnected my ecu yesterday and that didnt work. i was doin some reading in my bentley manual earlier today with the wiring diagrams and i think that its go something to do with ground number 137, where ever that is. bentley says its a ground connection in the motronic mfi wiring harness. any ideas where that could be located?

    10. Member dudeman08's Avatar
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      04-18-2011 04:45 PM #10
      also, yesterday in my attempt to fnd something knocked loose, i tapped my arm against the wiper stalk on the column and the wipers went up but didnt come back down.

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      04-18-2011 05:56 PM #11
      Quote Originally Posted by dudeman08 View Post
      also, yesterday in my attempt to fnd something knocked loose, i tapped my arm against the wiper stalk on the column and the wipers went up but didnt come back down.
      How is your relay #8
      It's the intermittent wiper relay

    12. Member dudeman08's Avatar
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      04-21-2011 02:33 PM #12
      well, i fixed the issue with the wiper. stupid me, i started doin some body work and deleted the fender mounted antenna but i tucked it under the cowl and the arms for the windshield wiers got it caught in the middle. thats fine now. i dropped my fuse/relay box and nothing seems loose. i resecured all the relays and what not. next step is to disconnect and reconnect everything on the back of it. any other ideas of what to do?

    13. Member dudeman08's Avatar
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      04-23-2011 09:23 PM #13
      bump.

    14. Member dudeman08's Avatar
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      06-17-2011 05:21 PM #14
      bringing this back from the dead since i just got some time to work on the car after doing the heater core and swaping the dash. i did some trouble shooting 2 days ago and this is what ive come to thus far:

      battery voltage: 12.1

      ignition switch is ok, it gets power and does all of its functions. (on, acc, and "start" position all have power. cranks like a champ and everything on the instrument cluster works, minus the cel lighting up like it should.)

      ignition coil: recieves the 12.1 volts the battery is putting out.

      voltage at the fuel pump fuse: 0.4 volts, i assume this is the refference voltage. (correct me if im wrong and give me specs please.)

      Fuel pump relay is gettin no power with the key in the on position and of course, you cant hear it. (had my dad listen through a pry bar against the filler neck.)

      fuses 15 (engine electronics) and 18 (fuel pump, heated o2 sensors) are ok. havnt checked the power to them yet.

      can anyone else think of anything else to check? im going out to do more trouble shooting once the weather clears up a bit. everything is plugged in on the relay/fuse panel, aside from some free hanging plugs from the harness in that area, which i assume are for optional equipment that wasnt in the car. (i know that many car companies make 1 harness and install it in all cars whether or no they came with certain things to save money and leave the ones that arent in use dangle there in the mess of wires.)

      all help is greatly appreciated.


    15. Member greyhare's Avatar
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      06-17-2011 06:38 PM #15
      Do you have a Bentley manual? If so you need to look at schematic 97-388.

      You are not getting 12v at fuse 18? (Fuel pump fuse)

      You are getting 12v at the coil? Fuel pump relay control power and coil power are both buss 15. (switched 12v.)

      The ECU turns on the pump relay by controlling the ground.

      No power at F18 means:

      A; pump relay is bad
      B; no control signal from ECU
      C; wiring fault

      Have you scanned for codes?

      Pull relay 12 (fuel pump)
      Check for 12v at terminal 8/30 (This is bus 30 B+; the relay switches this for the pump.)
      Check for 12v at terminal 2/88 (This is bus 15; should have 12v with key on.)

    16. Member dudeman08's Avatar
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      06-17-2011 06:49 PM #16
      yes sir, i do have a bentley manual.

    17. Member dudeman08's Avatar
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      06-17-2011 06:53 PM #17
      ok, im looking at that schematic now. ill have to out to the car and take a look. could the relay being bad cause the cel not to light up?

      also, i cant check for any codes because the ecu isnt communicating with anything.

    18. Member dudeman08's Avatar
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      06-17-2011 07:33 PM #18
      ok, i just went out and checked again. im only gettin 0.4 volts still at fuse 18 for the fuel pump. (yellow 20 amp) i also checked the fuse 15 (engine electronics) for voltage and it was 12 volts.

    19. Member dudeman08's Avatar
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      06-17-2011 07:50 PM #19
      i just checked the voltage on t-30 for the f/p relay and got 12v there as well. any ideas what to check next?


      also, i just noticed that the relay is a little discolored on one side. its the origional one. the relay is gray in color, but one section has a light brown hue to it. could it be burned out?
      Last edited by dudeman08; 06-17-2011 at 07:53 PM.

    20. Member dudeman08's Avatar
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      06-17-2011 09:55 PM #20
      thanks for the help so far, btw. i atleast now have a direction to run in. just got back in from doing some more trouble shooting. since the last update earlier, ive covered a lot of ground.

      fuel pump fuse (#18): still only 0.4 volts

      engine electronics fuse (#15): 12 volts

      terminal 30 for fuel pump relay: 12 volts

      checked fuel pump relay terminals 30 & 87 (as per what bentley said) and got 12 volts.

      i disconected the ecu and checked for the constant voltage to it ( T-1 (-) & T-54 (+)): 12 volts

      i also hardwired the fuel pump to check and see if it opereates and it was good. primed for the 3 seconds that it normaly does.

      what should i do next?

    21. Member greyhare's Avatar
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      06-18-2011 09:57 AM #21
      Do you have 12v at ECU pin 23 with the key on?

    22. Member dudeman08's Avatar
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      06-18-2011 01:49 PM #22
      im not sure. i didnt check that one. ill go out in a few minutes and check it out.

    23. Member dudeman08's Avatar
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      06-18-2011 07:07 PM #23
      yes sir, i did get power at terminal 23. got the 12 volts that the battery is putting out.

    24. Member dudeman08's Avatar
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      06-19-2011 10:38 AM #24
      happy fathers day bump!

    25. Member greyhare's Avatar
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      06-19-2011 11:29 AM #25
      Does the CEL turn on at initial key on?

      No ECU communication, continuous power to ECU, switched power to ECU. I hate to say it but you may have a DOA ECU.

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