What can cause an ECU failure?

Discussion in 'Mechanics Garage' started by philinnc, Jan 11, 2022.

  1. philinnc

    philinnc New Member

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    or perhaps more appropriately--how to determine if the ECU has failed?

    My '99 was idle for several years while I underwent cancer treatments. I am now in remission (hooray!) and want to revive my bike. I replaced the fuel pump, filter and submersible fuel lines. Spark plugs. The fuses are all good. The engine cranks but doesn't fire. I grounded a spark plug and it is arcing. I sprayed carb cleaner down the throats and it ran for a few seconds.

    After clearing the self-diagnosis the FI light is on constant. According to the service manual that could indicate a faulty ECU. I removed the ECU connections and sprayed with electrical contact cleaner.

    Before I buy a replacement is there anything else to check? The bike was stored inside and was running fine. The odometer reads just over 14K miles.

    As always--thank in advance!
     
  2. Grum

    Grum New Member

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    Glad to hear you are in remission, all the very best for the future.
    Do you have a wiring diagram of your bike? Do you have a multimeter and know how to use it?

    - Do you hear the Fuel Pump prime for approx 2 secs every time you turn the Ignition Swith to ON (Kill Switch to RUN)?
    - Is your bikes SideStand DOWN? If the ECM has a fault code it will ONLY flash the code with the SideStand in the Down position.
    - Is your battery healthy and its connections clean and tight?
    - Assume it has fresh fuel?
    - Also concerned for how long your bike was stored for. You may have gummed up the Injectors!

    The FI light permanently ON can also mean a loss of supply power on the Black/White wire to the ECM, or a bad Ground situation most commonly in the Orange Ground Block embedded in the wiring harness above the chain guard area.
     

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    Last edited: Jan 11, 2022
  3. philinnc

    philinnc New Member

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    Thanks for the comments.

    Yes to the wiring diagram, multimeter, fuel pump prime and side stand down.

    Is the ECM receiving power if the spark plugs, engine spinning, instrument panel functions and lights (turn signal, brake and headlight) are all working?

    Such fun!
     
  4. Grum

    Grum New Member

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    If your are hearing the Fuel Pump prime and you have a spark that would mean the ECM is at least partially working.

    - Is the FI Light On with full brightness or dim? This could indicate an issue with the Orange Ground Block mentioned?
    - Does the FI light blink when turn signals are activated, this can also point to an issue with the ground block?
     
  5. philinnc

    philinnc New Member

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    The FI light is bright and doesn't change intensity when the turn signals work.

    The manual shows that the black/white wire comes to the ECM via the gray multi-plug, however the factory uses a test pin box to measure the voltage. I assume this is the prevent an accidental short if trying to measure voltage using just the existing plug. I didn't see any listing of the relevant pin location in the plug itself.
     
  6. Grum

    Grum New Member

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    Assume you have removed the diagnostic shorting link you used when clearing the ECM memory?

    You should verify Grounds and Volts at the ECM.
    - According to the info I have GROUNDS are on A9 and A20 (Black Connector) both Green/Pink wires and B1 Green wire (Gray Connector). Make sure these measure near zero ohms back to the Battery Negative Terminal.
    - Make sure you are seeing near battery voltage at B8 Black/White wire, Ignition to On.

    See if you can back probe the pins or you may need to remove the plugs from the ECM to measure.
     

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    Last edited: Jan 11, 2022
  7. Grum

    Grum New Member

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    To answer your original question. "What can cause an ECU failure?

    The most common one I know of is over voltage. An R/R can fail and output can be in excess of 17v, failure of the ECU, blowing globes and cooking your battery can be the result.
    Generally ECU's are an incredibly reliable device and most common failures apart from the various sensors are failures of any of the multiple Grounds or Power source the ECU requires.
     
    Last edited: Jan 11, 2022
  8. squirrelman

    squirrelman Member

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    if you get sparks to all 4 plugs the ecu is probably fine.
     
  9. philinnc

    philinnc New Member

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    Yes, I removed the shorting wire after clearing the memory.

    Backing up a bit--during my cancer treatment I'd start the bike every month or so. At some point the battery got too low to start it--so it sat for a number of years. It had been running fine, so I doubt that the electrical system experienced any over load, etc. from the diminishing battery. I have another bike (Aprilia) that is showing the exact same symptoms--spark but no spray from the injectors. Perplexing.
     
  10. Grum

    Grum New Member

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    That fact you are getting a spark is a good sign, but the fact your Fi light is permanently On is Not. Fi Light should go out after Fuel Prime at Switch On. Even if your injectors were gummed up this would not cause the Fi light to be permanently On.
    The Fi Light being On and Not flashing a fault code with the SideStand Down more often than not means power or one of the Grounds is not good, that fact you have spark would mean the power source is good but what about the Grounds? There are three ECU Grounds as well as the Signal Ground, various systems eg Fuel Pump control, Injectors and Ignition may use either one of these Grounds it all depends on the internals of the ECU.

    Injectors will reach an operational threshold where they will not fire so it's why the state of your battery and connections were mentioned. Does the bike crank over at the normal healthy rate? A battery sitting idle for month after month will be destroyed in time by the effect of sulfation, always good to connect your battery to an intelligent charger/maintainer for lengthy periods of non riding. Any doubts about the battery, charge it then take it to an Auto Parts supply store where they will load test the battery for you. (In Australia there's no charge for this service).

    ALWAYS - The first thing to be absolutely sure of when chasing any electrical issue is that you are working with a known good healthy Battery. AND immediately you get the engine running is to confirm your charging voltage at the battery at idle and 5000rpm. Normal charging voltage should be around 13.5 to 14.5volts.
     
  11. philinnc

    philinnc New Member

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    I can check the grounds. The battery is brand new 2 weeks ago--purchased along with the new fuel pump and filter. The motor spins healthily (is that a great description or what?)
     
  12. Grum

    Grum New Member

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    Just had a thought! A long shot but needs verifying.

    Is the wiring of your SideStand switch normal? Some people decide to short out the SideStand switch instead of replacing a faulty one.
    The effect of a shorted out switch (permanent UP position) will be that if the ECU detects an active fault then the Fi light will be permanently On and the flashing fault code cannot be displayed.
    It will also effect the protection of shutting the engine down if you are in gear and the SideStand is lowered.

    Try This - With the SideStand DOWN, bike In Gear, Clutch Pulled In. Ignition ON, Kill Switch to RUN.
    Now hit the Starter Switch, (KEEP THE CLUTCH PULLED IN) if the engine cranks over then the SideStand Switch is either shorted or bypassed.

    Also you mentioned you cleared the stored fault codes. Did you record what the codes were?
     
    Last edited: Jan 12, 2022
  13. philinnc

    philinnc New Member

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    I just tried that--the engine does not crank. The clutch interlock switch is also functioning--in neutral the engine cranks regardless of whether the clutch is in or out, but in gear it will only crank if the clutch is pulled in.

    Before I cleared the fault codes there was a continuous blink--that continued even after 24 blinks. One blink, pause for perhaps 3 seconds, blink again, repeat. Because that didn't correlate with any of the malfunction blinks, I cleared the memory.
     
  14. philinnc

    philinnc New Member

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    I removed the connectors and the grounds show near zero ohms, battery voltage at B8. Is the next step ECM replacement? I have found a used 38770-MBG-671 (US and Canada version) for sale.
     
  15. raYzerman

    raYzerman Member

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    Whether the grounds measure zero ohms or not, I'd clean them all up nice and fresh to be sure of good grounding. Frame ground on the right side and the ground spider on the left side taped into the harness.
     
  16. philinnc

    philinnc New Member

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    Will do--the adventure continues!
     
  17. Grum

    Grum New Member

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    One blink pause and repeat sounds like you had a Fault Code 1 = MAP Sensor issue!

    So are you saying that ONLY since doing the ECM memory clearing that you now have the Fi Light fully On? If so could this mean the clearing process wasn't done correctly? Might be worth trying the process again.

    Agree with raYzerman, check the Orange Ground block embedded in the harness above the chain guard. This is a ground junction where many devices have the ground wire come in to. From memory only two of the Green wires actually go to Ground and all other wires are buss barred to the actual Ground wires.
    Remove the joining buss bar and check for any burnt pins and sockets, see attached photo.
    If everything is fine with the Ground block then you may well be looking at a replacement ECM, if so make sure it is exactly the same part number as what's on your original.
     

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  18. philinnc

    philinnc New Member

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    In the service manual the procedure for clearing the memory states:

    Side stand down.
    Ignition OFF, engine stop switch in RUN position.
    Short the connector with a jumper.
    Ignition ON.
    Remove jumper.
    The FI indicator goes on for 5 seconds.
    Insert jumper while the light is on.
    The indicator turns off and starts blinking.

    For me, following that procedure, the last step never happens, that is--after the jumper is reinserted the indicator light stays on. Never blinks.

    If I remove the jumper, with the side stand down, engine stop switch in RUN position, ignition ON--the FI indicator comes on for a few seconds (then goes off), the fuel pump primes and the dash information is displayed. The engine cranks but doesn't fire.

    NOTE: This is a CHANGE from a few days ago--back then the FI light stayed on after clearing the memory. Now it blinks once and stays off (I'm assuming that this happens normally when everything is OK). The manual states--"If the malfunction indicator does not light or blink, the system has no memory of problem data."

    What's happening?
     
  19. philinnc

    philinnc New Member

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    If the 'blink-pause-blink' was a MAP sensor issue, now that the memory has been cleared how can I recreate the problem that resulted in the single blink (to confirm that there is a problem)?
     
  20. squirrelman

    squirrelman Member

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    grum is the maximum 'lectickal expert, so go by what he says. i say if you have 4 sparks at 4 plug wires, there is nothing wrong with the ecu.

    maybe you could borrow one to test.
     
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