Immobilizer flakiness on my '99 EX - voltage related?
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Thread: Immobilizer flakiness on my '99 EX - voltage related?

  1. #1
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    Immobilizer flakiness on my '99 EX - voltage related?

    I'm having some intermittent issues with my immobilizer system on my '99 EX. Years ago, I used to think it was one of the keys that was flaky, but now it seems to have problems with all keys and appears voltage related.

    Does anyone have any info on the voltage-related aspect here? Like what particular component could be failing and what a fix could be (both long term and emergency)?

    I'm well aware of how the immobilizer is supposed to work, I watch the green light, etc. There is no problem at all with battery voltage to crank the engine. It is just the immobilizer that prevents starting.

    For example, recently, after the car had been sitting for a while, I went to go and start it. After turning the key to ON, the green light was flashing so I knew it would not start. Tried anyway = strong crank but no start. Changing keys made no difference. All accessories turned off. Measured voltage at the battery posts and the cables and it was 12.0V. Yes, a little low, fitting this pattern I have been noticing. I put a charger on it, and it did not start immediately, but after getting up to 12.3V the immobilizer let it start.

    This sort of thing (not always measured carefully, though) has been happening more often lately. I expect things will continue to get worse until it just won't start at 12.6+V.

    I'd of course be happy with a solution that completely removed the immobilizer system. I'm kind of like this guy:

    2011 Odyssey LX, 74k miles
    1999 Odyssey EX, 230k miles, original owner

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  3. #2
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    Any and I mean any electrical oddity and if the battery has more than 2 years on it, I put a new one in before even bringing the voltmeter out.

  4. #3
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    Thanks for trying to help. From my observations, I'm pretty sure this problem is related to the battery voltage. So yes, putting in a new battery or always making sure my battery is 12.6+V before putting in the key would mean I would not see this problem. But the problem would still be there, perhaps getting worse, waiting until the voltage (new battery or not) drops a little below the limit.

    So I'm trying to figure out the weak component and fix/replace/bypass it. Trying to diagnose the problem rather than hide it. The battery has plenty of voltage to strongly crank the engine, etc. Just not enough to pass the immobilizer test.

    Also a call for similar experiences - has anyone noticed voltage-related problems with the immobilizer system.

    Is it possible to bypass the immobilizer system without building my own ECU from scratch?


    Sontakke - on the new battery idea, I generally think similarly. In fact, I've made it so I use the same battery in 3 of my cars (including the two Odysseys) and if there is ever a weird electrical thing going on, swapping batteries between cars is a debugging step I will take without much hesitation. But here, I have no doubt it is voltage related and want to track it down and fix it. I have found on other systems that this region between working perfectly and completely failed is a good place to isolate failure points.
    2011 Odyssey LX, 74k miles
    1999 Odyssey EX, 230k miles, original owner

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  6. #4
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    Quote Originally Posted by oldskewel View Post
    Is it possible to bypass the immobilizer system without building my own ECU from scratch?
    LOL

    It might be possible if you ground pin 1 on the main relay. (You could ground pin 1 by connecting it to pin 3, the ground for the first stage control circuit of the main relay which activates the immobilizer.)

    That should perpetually complete the main relay second stage control circuit which activates the fuel pump when the key is ON or START, rather than using the PCM to ground the circuit. So the fuel pump should run regardless of the immobilizer.

    Note that the 2-second fuel pump priming feature would be lost. The FP would run as long as the key were ON.

    This is just a theory. Double-check it carefully using a wiring diagram before you try it.

    Dave
    2002 Odyssey EX Fern (Granite) Green
    Honda hood protector, stainless steel flex brake lines, Honda block heater, AC condenser screen, Zymol wax
    141,000 miles/227,000 kilometres; original transmission; Amsoil MV ATF since 79,000 miles/127,000 kilometres; Magnefine aux ATF filter; Honda aux ATF cooler; 18 drain and fills

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    Quote Originally Posted by davedrivesody View Post
    LOL

    It might be possible if you ground pin 1 on the main relay. (You could ground pin 1 by connecting it to pin 3, the ground for the first stage control circuit of the main relay which activates the immobilizer.)

    That should perpetually complete the main relay second stage control circuit which activates the fuel pump when the key is ON or START, rather than using the PCM to ground the circuit. So the fuel pump should run regardless of the immobilizer.

    Note that the 2-second fuel pump priming feature would be lost. The FP would run as long as the key were ON.

    This is just a theory. Double-check it carefully using a wiring diagram before you try it.

    Dave
    Thanks for the idea - just the sort of thing I was looking for. I'll look into it. So is this basically "hot-wiring" the fuel pump, or is it any more than that? I.e., I will still see the flashing green immobilizer light (no problem if so, I would just remove the bulb). Does this mean that the immobilizer system just works by disabling fuel, and leaves ignition on?
    2011 Odyssey LX, 74k miles
    1999 Odyssey EX, 230k miles, original owner

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    This whole thing is rather interesting, the immo is just an RFID chip excited by the antenna in the ignition.

    Defeating the immo isn't quite that simple, the K20 and K24 cars (RSX, TSX, Accords, etc) that frequently donate their engines to other cars are also immo equipped and Hondata does reflash the ECU to disable the immobilizer. If it was a simple wiring change, everyone and their mothers would be doing it that way when swapping these K20s into Civics and whatnot. But who knows, there is always the 'first' guy who did it... so maybe you are 'that guy'.

    The ignitions on these cars are known to be flakey, how certain are you that the problem is immobilizer related? You say in your first post you know how the immo is supposed to work, and I can appreciate that. But sometimes honestly, the simplest things elude us... I know all about it, I started chasing down a problem that was pointing toward a bad ECU when the whole time I was missing the fact that the check engine light bulb had burned out in the cluster and the check engine code was causing the symptoms I was seeing (TCS light being illuminated). Like I said, the simplest things.

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    So to expand on how (I think) the immobilizer system is supposed to work ...

    When it's working normally:
    I put the key in, turn it to ON. The green light turns on solid green (NOT flashing, as if to reassure me that the immo system has been checked and cleared for takeoff) for a few seconds and then turns off. I can then continue to start the car. After turning the car off (from ON to ACC), the green light will flash 5 times before going dark like the rest of the instrument panel. I expect this shutdown flashing is an indication that the immobilizer system is arming itself again.

    When it's NOT working normally (i.e., this problem that I believe to be voltage related will prevent the car from starting):
    I put the key in, turn it to ON. The green light starts flashing and never stops.
    If I then turn the key to START, it will crank strongly but will not start. Green light still flashing. So the battery is plenty strong to do everything except make the immobilizer work correctly.
    At that point, I can measure the battery voltage, see it is low, and connect a charger that will gradually bring up the voltage.
    While this is happening, I can periodically put the key in, turn to ON (no need to try to start if the green light flashes) and wait until the green light comes on solid. Then it will start just fine.

    So to me, there seems to be a clear connection between that green light flashing and having the car start/not start. And the green light will flash vs. go solid green depending on the battery voltage. And I have had the same results with 3 different keys (one of them a valet key), so I don't think there is a problem with the keys.

    Let me know if anyone has any ideas of tests to run next time my battery voltage drops.
    2011 Odyssey LX, 74k miles
    1999 Odyssey EX, 230k miles, original owner

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    Quote Originally Posted by oldskewel View Post
    So is this basically "hot-wiring" the fuel pump, or is it any more than that?
    Yeah, you could say that.

    Quote Originally Posted by oldskewel View Post
    I will still see the flashing green immobilizer light (no problem if so, I would just remove the bulb).
    Yes, the immobilizer and its light should still work as normal.

    Quote Originally Posted by oldskewel View Post
    Does this mean that the immobilizer system just works by disabling fuel, and leaves ignition on?
    Yes, that's right. The immobilizer system only cuts the fuel. It does not affect ignition.

    Dave
    2002 Odyssey EX Fern (Granite) Green
    Honda hood protector, stainless steel flex brake lines, Honda block heater, AC condenser screen, Zymol wax
    141,000 miles/227,000 kilometres; original transmission; Amsoil MV ATF since 79,000 miles/127,000 kilometres; Magnefine aux ATF filter; Honda aux ATF cooler; 18 drain and fills

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    Have you checked the voltage *before* cranking and have determined that when the green light is flashing *before* attempting the crank, voltage is lower than when it does not flash? What I am suggesting is that may be voltage measurement is dependent upon if the car was cranked and not started vs flashing and not flashing.

  12. #10
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    Yes, since I am aware of the green light being solid vs. flashing, I first turn the key to ON and look for the light. When flashing, I then check voltage before cranking (which I know would reduce voltage).
    2011 Odyssey LX, 74k miles
    1999 Odyssey EX, 230k miles, original owner

  13. #11
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    A bad ground to the immobilizer (in theory) could indeed cause it to behave like this. If there is a corrosion, the effective resistance of the circuit could make it NOT behave correctly once the voltage drops slightly. Obviously, we are all guessing here.

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    Interesting issue. Makes you wonder if when it happens you could attach a portable jump starter to it and have it work fine. Or even one of these: Lithium Ion Jump Starter and Power Pack
    Mike
    2000 Odyssey LX
    Trans at 82k -- Tru-cool trans cooler
    DIY Timing Belt at 104k
    Hidden Hitch & Airlift 1000's

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    Quote Originally Posted by OdyinNH View Post
    Interesting issue. Makes you wonder if when it happens you could attach a portable jump starter to it and have it work fine. Or even one of these: Lithium Ion Jump Starter and Power Pack
    Yes, I've been thinking along those lines. But knowing it does not need the amps to do an actual start (as these portable devices normally provide), but just to raise the voltage enough to make the immobilizer happy, I've been thinking of using a cordless power tool battery, which I already have plenty of, and would be easy to carry, etc. Currently waiting for a need to pursue all these ideas.
    2011 Odyssey LX, 74k miles
    1999 Odyssey EX, 230k miles, original owner

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    K went over the literature on this problem.

    davedrivesody is spot on. the ECU processes the coded signal from the key receiver and sends the enable to the main relay. There is no indication that the ECU does anything different after that, meaning if you jumpered out the enable signal and went straight to ground, instead of relying on the ECU to control the fuel pump, there should be no ill effects aside from having no prime. I don't recommend doing this. It should work, but I'm one to think if it came with the car, it should work. Not just rip out things as they become nuisances. So, let's see if we can get you a fix.

    It clearly seems like the ECU and the main relay and the indicator light are doing their jobs. So we will ignore those. It also sounds like you have checked fuses 13, 1, 46.

    There are two possibilities. One, the receiver unit isn't reading your signal from the keys and two, it is reading the signal but the signal isn't making it to the ECU. In any case, the action will be around the key cylinder. How good of a multimeter do you have? Will it read to x.xxV or is it just x.xV? Under the steering column cover, find a grey 4 pin connector with yel/blk, blu/grn, org/blu, and blk or brn/blk wires. It should be to the right of the tilt steering lever, possibly wrapped in foam. I want the voltage between yel/blk and a GOOD SOLID GROUND. then I want the voltage between yel/blk and blk (or brn/blk). Then check the resistance between brn/blk (or blk) and your GOOD SOLID GROUND. If all seems good here, then unplug the 5 pin connector of the immo receiver located behind the ignition switch (where you put the key in, not the actual switch itself)... should be above the key opening and up toward the gauges a little. That is the actual immo receiver, do the same tests at that plug. Are the readings any different? Wiggle wires while doing this, we're trying to find a loose or broken wire.

    If everything seems solid, then perhaps the signal from the immo receiver is getting lost to the ECU. The wire responsible for carrying this signal is blu/grn from the receiver to the grey plug, then that wire should be red from the grey connector all the way back to the ECU pin A25. Unplug both sides and check continuity of that wire while wiggling stuff around.

    Let us know what you find.

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    oh, and if the voltage between yel/blk and a good ground does not equal voltage at the battery, check the same at the main relay. If the voltage at the yel/blk main relay is still different from the battery, then check voltage of the main relay between wht/grn and a good ground. if that voltage is STILL different than battery voltage, go back to the underhood fuse box and check voltage at fuse 46.

    I'm inclined to think inside the cabin you won't find bad grounds or rotten connectors... but you might in the underhood fuse box.

    Also, let's give sontakke credit here too, he does have a valid point. The ground responsible for the immobilizer is actually located on the transmission side of things under the hood. It is located under the throttle body, under one of the big radiator hoses. Good chance that's quite rotten looking also.

    But rather than stabbing at the problem, perform the aforementioned tests and we will have an answer immediately. IF the voltage differs between yel/blk and GOOD ground to yel/blk and brn/blk (or blk) at the grey connector under the steering column, then go after the ground under the throttle body. If the voltage is the same, then go backward toward the main relay and underhood fuse box.
    Last edited by bbarbulo; 02-08-2017 at 02:03 AM.

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