Immobilizer flakiness on my '99 EX - voltage related? - Page 2
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Thread: Immobilizer flakiness on my '99 EX - voltage related?

  1. #16
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    Thanks for the very detailed troubleshooting steps. I'll go through all these when the problem forces me to, or I have the time and energy to do it before that (I can always drain the battery on purpose if needed to simulate the failure condition).

    Couple of things to know about this situation, though:

    Due to the climate out here in CA where I am, there is very little corrosion anywhere on this van. I actually removed, inspected, and re-soldered a couple of joints in the main relay a few months ago, and my 17 year old 230k van's main relay circuit board looked 10x better than any of the photos of the repair. It was a pre-emptive check/repair just because a few others were finding problems with the main relay.

    I think I've pretty well narrowed this problem to be related to battery voltage. I know sometimes flaky electrical connections can be voltage-dependent, but here I'm observing reliably that 12.0V is too low and 12.3+V is OK, which is a pretty close range, so I'm not really expecting that wiggling wires will provide the difference required to satisfy the immobilizer with only 12.0V at the battery. But I'll do these tests anyway.

    I've got no problem modifying the car to bypass this if it is a good, reliable solution. For example, doing the main relay hot-wire, but with a switch in there so I only do it when needed. I'd just label the switch "initiate self-destruct sequence" so none of the car thieves trying to take my sweet old ride would use it to circumvent the immobilizer.
    2011 Odyssey LX, 74k miles
    1999 Odyssey EX, 230k miles, original owner

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  3. #17
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    you needn't simulate the failure, you can do this anytime. What we are looking for is a difference from battery voltage. So if your battery voltage is 12.7 and everything is working well, maybe the immobilizer is only seeing 11.4 and barely hanging in there. So by the time battery voltage is 12.3, the immobilizer hasn't the range to 'excite' the RFID chip anymore.

    While it is true that nasty weather makes for nasty looking electrical (and body, and bolts, and carpets, etc ), that isn't always the case. Oxidation happens anywhere there is oxygen. Normally we rely on soft metals like brass or copper to conform and create a connection (and air tight seal), but anywhere air can get it, you start to get corrosion. So while it may not look gnarly, if that connection is loose air will get in and start to form a layer of oxide which doesn't conduct. Given your symptoms, a failure exists. If all this checks out, then get a junkyard or new immo reader unit. There is no programming to be done, the immo reader is just that, the ECU does the signal processing. But as long as we have ideas about repairing it correctly, let's not start to hotwire things please.

  4. #18
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    Yes, I realize the best thing would probably to take all the measurements with a 12.6V battery (with everything working correctly), then drain it to whatever it takes to kill the immobilizer, and take all the same measurements again. For a start ...
    2011 Odyssey LX, 74k miles
    1999 Odyssey EX, 230k miles, original owner

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  6. #19
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    No, for these tests you don't need to get the failure mode. That's the beauty. Getting the immo to fail will not change your results. It literally does not tell you anything since you can't read the coded communication to the ecu. So you will never know if the immo info from they key is being sent to the ecu. All you can do is verify that the wire I said goes to a25 is intact.

    Think this through, what do you imagine getting the voltage to drop will do for your test? Formulate a hypotesis about the failure and imagine what readings would confirm or disprove it.

  7. #20
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    On my '03, the battery voltage got down to around 11.0 and 11.2v and it still started fine in 15F conditions. It is parked outside all the time.
    I replaced the battery shortly afterwards and the new battery stays around 12.2v after it is gets to its resting voltage ( off for a hour or so).
    While running, the voltage is 14.3 and later settles down some. With the old battery, it stayed at 14.3 v all the time it was running.
    Buffalo4
    2003 EX-L
    168k miles orig tranny Oct 2015

  8. #21
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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
    Still a theory, but I have double checked it carefully now.

    One slight modification, to minimize any chance of ECU damage, is to isolate the pin 1 connection from the ECU-side before grounding it. Other than that, it looks like yes, the immobilizer simply disables the fuel pump. So bypassing that should allow the car to run.

    I've attached scans from the service manual for my '99, including a marked up one of the main relay + immobilizer system, in case it helps anyone.

    Other than that analysis, I have not been able to do much (e.g., all the voltage testing trouble shooting). Not much time / energy.

    But over the weekend, I did try as hard as I could to recreate the failure mode (swapping in other batteries, with low voltage in the single digits, etc.; key wrapped in aluminum foil RF shielding) and was unable to do it! The immobilizer cleared every time, even when the battery was almost dead. Very interesting result there - suggests that maybe the low voltage is correlated with the immobilizer failure but NOT the cause of it. But it does not quite explain why charging the battery slightly will restore immobilizer function, which I have observed multiple times.

    Marked up circuit diagram of the immobilizer / main relay circuitry:

    main relay immobilizer circuit marked up - small.jpg

    Trouble shooting steps (3 pages)

    immobilizer debugging manual scan_Page_2.jpg

    immobilizer debugging manual scan_Page_3.jpg

    immobilizer debugging manual scan_Page_4.jpg

    Main Relay

    honda99 main relay.jpg
    Last edited by oldskewel; 02-14-2017 at 08:03 PM.
    2011 Odyssey LX, 74k miles
    1999 Odyssey EX, 230k miles, original owner

  9. #22
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    So much effort in making something that can work... not work.

  10. #23
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    Update on the immobilizer fuel-pump hot-wiring ... attempted and it does NOT work.

    I did the steps listed above, and was successful in not damaging anything (un-did it all afterwards), and it DID make the fuel pump run constantly.

    To simulate immobilizer failure, I did not use a key at all. I disconnected the electrical part of the ignition switch and turned that with a screwdriver, after implementing the main-relay fuel pump hotwire.

    The fuel pump ran continuously (clearly heard the fuel flowing with the hood raised - this was easier to hear than the actual fuel pump running inside the fuel tank), the car cranked strongly, but it did not start.

    Actually the very first time it ran, I blew the #46 15A fuse in the engine bay. Not sure why. After replacing it, things were fine. So it could have been a flaky fuse at the root cause of my immo problems. BTW, I have not had any immobilizer problems since diving into this. Hard to diagnose a problem that is not there.

    From the circuit diagrams, the ECU (PCM) does know in this condition that the immo is not happy, and it must be shutting off either fuel injectors (even though the fuel pump runs) or spark or both. The service manual has an abstract diagram showing how the immo controls the fuel system, so it's likely to at least be the fuel injectors that do not fire.

    In hindsight, of course it does not work. It would not be much of an immobilizer if it did. But I found it an interesting experiment. From googling after the fact, I see how others have disabled the immobilizer by opening the ECU and removing the coded chip or two (that works, but disables OBD and gives a CEL). They can then replace the chip with a dummy, which solves those two problems. But it seems people only do that when there is no other choice (not my situation).

    I followed the voltage/resistance debugging steps in the manual and in bbarbulo's comments, without finding anything noteworthy, although I did not get to the point of measuring resistance from the immo to the PCM (not convenient, and really, I know the thing is working, so everything is checking out OK now).

    I even took the immobilizer transceiver ( 39730-S84-A02 ) out, popped the cover off, measured what I could and re-flowed one less than perfect solder joint (#1 = power). All seemed just fine. Very simple device.

    At this point, with things apart and the immobilizer in hand, my options seem to be:
    1. Put it back together, hoping that it was the flaky fuse, or maybe also other flaky connections (I found a few screws loose from the dealer's last [recall/warranty] ignition switch install) I fixed will make it never fail. And if it ever does fail, I would be able to quickly replicate the debugging steps (basically just check for power and ground to the immo, and check continuity on the two signal wires back to the PCM).

    2. Buy and install a new immo ( 39730-S84-A02 ) - a few days to get it and $70.

    I'm leaning toward #2, but am surprised that I have not found other reports on this list of people needing to replace that part. Also that inspecting the part, it is incredibly simple - seems hard for it to fail; on the other hand, searching outside this list shows many people replacing it - but people often replace things they don't need to.

    Has anyone actually replaced this part?

    Also, for those of you who have fixed your ignition key tumblers, if I have no problems with that, is this a good time to get in there for some preventive maintenance?

    If it fails to start one day in front of my house, I'll be happy. If I'm 200 miles from home in a snow storm ...
    2011 Odyssey LX, 74k miles
    1999 Odyssey EX, 230k miles, original owner

  11. #24
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    I reinstalled it just now. Pretty fast to do, actually, now.

    I had called around to my 2 local dealers about the part. Neither had it in stock. One mentioned that it has been discontinued (something I noticed also online at some vendors). One guy really had no idea how common it was for these to fail. The other guy seemed more knowledgeable and said they generally only get replaced when there is physical damage to the ignition key area, such as in a failed theft attempt. Anyway, that was enough info for me to give it another shot before replacing it.

    Another thing I noticed was that the dealer who replaced my ignition switch a few years back had given me an extra cable that I don't need, so I removed it. It probably saved them 2 minutes when they replaced the ignition switch, and who knows, may have been the cause of the flakiness. Here's a photo:
    IMG_8927.jpg
    The ignition switch assembly has both of these connectors, but rather than use those when they replaced the ignition switch, it seems they used this extender/adapter instead. Maybe this allowed them to do the replacement with fewer disassembly steps. The 5P green connector in the photo was the one going to the questionable immobilizer part, so it definitely could have been related. Now that it's gone there's one less thing that could be causing the problem.
    2011 Odyssey LX, 74k miles
    1999 Odyssey EX, 230k miles, original owner

  12. #25
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    oldskewel, thanks for trying this out.

    It's valuable to know that an invalid immobilizer signal also shuts down the fuel injectors. Actually, it makes sense. There could be enough fuel pressure in the rail to start and run the engine a short distance. That might be long enough for a thief to get it onto a flatbed, thus negating the security of the immobilizer.

    Best of luck resolving the original problem.

    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

  13. #26
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    IF the new immobilizer works, I'll be glad to hear. I had a different immobilizer situation. Going back a year, I had made plenty of complaints about my non-starting van, with symptoms exactly like yours: sitting for a short time, etc. Meanwhile I have been dealing with a lack of ACC outlet power. The PO's kids I think tried to jerry-rig a separate run of ACC power straight off the battery. I had a pretty extreme power drain that actually destroyed 2 batteries. I removed that power run and all of a sudden the power drain was gone AND also the immobilizer issues. So IOW, find the short, solve the immobilizer problems.
    00 Odyssey EX - 290K some restoration plus Acura leather wheel, Civic bucket seats, Kenwood and Sony sound
    04 Volvo V70 T5M - turbo, stick, Konis, swaybars: a real Sport Utility Vehicle
    06 Mazda5 - the runabout

  14. #27
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    We're the original owners on this van, and other than recall/warranty stuff (ignition switches, transmissions) I've kept it out of the hands of others, so I'm pretty sure there's nothing crazy going on with a wiring mod. Although as I showed in post #24, the dealer snuck in an extra wiring mod (should have had no effect, but it was an extra thing to go wrong).

    Being flakily intermittent, it is proving really tough to troubleshoot. At this point, I'm thinking there is some wiring somewhere that is marginal, but it seems I need to wait for a failure and then hope it does not fix itself before I trace it down. If I had to do something blindly, I'd start replacing ground straps before replacing the immobilizer transceiver. And I might just start doing that. I bought a box of new fuses too.

    So rather than a short, I expect it is a marginal ground.

    Back to my very original voltage-related theory - I still think it _is_ correlated, but not the cause of the problem. So if a ground somewhere is marginal, then increasing system voltage slightly might fix it - that makes sense. But on the other hand, if the grounds are all good, then lowering system voltage will not cause the problem to appear.
    2011 Odyssey LX, 74k miles
    1999 Odyssey EX, 230k miles, original owner

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