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I was asked to look at a Lexus ES330. The complaint was the car wouldn't go over 20MPH and would fall on it's face. The ECM was replaced and problem persisted. One coil was replaced around a year prior. Verified the complaint, car was hitting fuel cut and in limp mode.

Check Engine light is on with the codes:
P0351
P0352
P0353
P0354
P0355
P0356

Codes would set immediately after starting the engine.


Put a wire loop into the IGN fuse and captured a parade pattern.

Yellow: #6 IGT signal
Red: Ignition Coils, Primary Coils

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It looks OK... I verified the secondary was firing with an adjustable spark tester.

Same capture zoomed out, you can observe the ECM stopping the injectors firing as it hits fuel cut.

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So, on Toyota's/Lexus's the ECM sends the IGT signal to each coil and in return each coil returns an IGF signal to the PCM in a parade pattern.

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I back probed terminal 24 on the E10 connector at the PCM and at the #6 IGF terminal.

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As you can see the ignitor isn't sending back a good signal. Or it's just noise from the IGT signal/primary coil ramping and the ignitor is not sending back a signal at all.

IGF vs #6 IGT

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So, the question. Why would all 6 coil ignitors fail at once? A power surge? A bad PCM driver? What would be a good test to determine the root cause of the failures?

I've heard tell of this happening, but have never run into this until now.

  • Real humdinger. For my curiosity, is 'T' for Trigger and 'F' for feedback? – Zaid Aug 12 '16 at 13:08
  • @Zaid That would be my best guess Toyota uses weird acronyms sometimes. – Ben Aug 12 '16 at 13:35
  • I read, can't remember where, that a cause could be if the ICM sticks in start mode too long, for whatever reason, when starting the car instead of switching to run, and if it sends a higher voltage to the coils in start mode, it could fry multiple coils if it sticks in start mode too long. Maybe that happened once and killed everything? I dunno much about it. The forum post was about Toyotas though. – Jason C Aug 12 '16 at 14:32
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    @JasonC It would be hard to test the coils off the car without some kind of setup to generate the trigger signal. Actually I just learned that all 6 coils may not necessarily be bad. When an ignitor fails it can pull down the IGF circuit causing all 6 codes to appear. It doesn't always happen but it can. As to the ignitor start signal question, I don't think that this style of Toyota COP ignitor does this. There's a constant 12v supply to the ignitor from what I've observed. More testing is required to see if one coil is truly pulling down the IGF circuit. – Ben Aug 12 '16 at 15:20
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    A thought: If the IGF lines are powered (and intended to be held high) when the ignition is on but not running, you might be able to do the test a lot more quickly and conveniently by just disconnecting coils without the engine running and checking if the line goes back up to 12V. – Jason C Aug 12 '16 at 16:15
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Well, you already found the big hint somewhere else:

Ben wrote:

It would be hard to test the coils off the car without some kind of setup to generate the trigger signal. Actually I just learned that all 6 coils may not necessarily be bad. When an ignitor fails it can pull down the IGF circuit causing all 6 codes to appear. It doesn't always happen but it can. ... More testing is required to see if one coil is truly pulling down the IGF circuit.

Possible ways to test that:

  • Disconnect / swap-in-a-known-good‌​-one one at a time and see if the signals return on the others (or just leave one at a time connected so it doesn't hide the issue if 2 or more failed in this way).
  • Maybe: If the IGF lines are powered (and intended to be held high) when the ignition is on but not running, you might be able to do the test a lot more quickly and conveniently by just disconnecting coils without the engine running and checking if the line goes back up to 12V. Not sure if that would work, but if it does, it means you can perform the IGF line tests with a voltmeter instead of a proper scope.

Another thing to do, if you have the ability, is to test the coils on their own not in the vehicle. Like in another car or on the bench, completely isolated from the problem car, to make sure the coils are actually failed and it's not some insidious electrical problem or other damaged part somewhere that's muddling the signals on otherwise fine coils. This is important so that you can determine if every coil did indeed fail vs. some other problem that just makes it look like they failed.

Other ideas when all (or many) coils appear to have failed at once, which may or may not have much merit because I have zero experience with the finer points of ignition coils:

  • I read, can't remember where, that a cause could be if the ICM sticks in start mode too long, for whatever reason, when starting the car instead of switching to run, and if it sends a higher voltage to the coils in start mode, it could fry multiple coils if it sticks in start mode too long. So I guess it's possible that that happened once and killed everything. I dunno much about it. The forum post was about Toyotas though. (The OP, however, did mention that this vehicle did not have a system like this.)
  • Maybe the wrong set of spark plugs all around somehow damaged the coils? Also no idea what I'm talking about just throwing things out there. My gut says this is unlikely.
  • In this case the ECU was replaced, ruling that out, but a failing ECU or electrical issue in that area could also always be a culprit, especially if the problem persists after exhausting other possibilities.

Somebody please correct me if those are stupid.

Should be noted that the OP's hypothesis of one bad coil holding down the IGF lines on the rest was the cause of the original problem here:

Ben wrote:

This one has been resolved the #4 coil was dragging down the whole circuit. They opted to replace all the coils due to age.

I don't have a lot of good ideas for future readers here but the important points are:

  • Test to verify that every coil actually failed vs. it just looking like they all did because of some other underlying issue.
  • In ignition systems with feedback signals, it is possible that one coil can fail in such a way as to hold the IGF lines down; the symptoms being the ones described by the OP: An apparently OK ignition sequence but lack of a good feedback signal and resultant ECU confusion. I'd also imagine even in non-feedback systems that the general pattern of "one failed X making it look like every X failed" could pop up, so do what you can to isolate the problem.

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