12P and DTC 46

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12P and DTC 46

Postby VK_3800 » Sat Aug 10, 2019 7:56 am

Hi all

The check engine light came on last night in the Torana, it ran as normal and didn't exhibit any problems (definitely not in limp home mode) but the light stayed on for the short trip. When I came home a few hours later it was off and has been ever since.

Checking the codes this morning it shows DTC 46 set (no ref pulses). Currently everything is working as normal, it starts and has a normal RPM signal. Obviously this was an intermittent thing as I didn't notice any issues whatsoever, even when the light was on it started right up as usual every time. I believe a complete loss of ref signal won't allow it to start at all?

Anyway long story short is this something that can potentially appear and not be an issue, or should I start pulling things apart looking for a fault before I end up stranded somewhere? Is it possible to reset the DTCs via Tunerpro/OSEPlugin or do I have to disconnect the battery?

Thanks

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Re: 12P and DTC 46

Postby antus » Sat Aug 10, 2019 11:20 am

I'd say it missed a couple of pulses and might have stuttered a tiny bit (would have missed an injection and/or spark pulses) but is working well enough to keep running. If its still running smoothly you could watch it for a while and maybe it'll go away on its own but it might be a sign something is on the way out, or an electrical issue is starting to form. Ignition module, the ecm itself, grounding issues. The DTCs are not carried over, so if it remains on after a power cycle the fault is still present. If you have some spare parts try swapping them over and see if it goes away. Seeing that but it still running smoothly makes me suspect the ecm itself. I think an ignition module problem would be more like to happen fast rather than slowly degrade.
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Re: 12P and DTC 46

Postby vlad01 » Sat Aug 10, 2019 11:55 am

I have had this a few times on my VR. Turned out it was just being tripped by low voltage during cranking from the battery being a bit low. Iirc one of the conditions for 46 related to voltage from the sensor or something being below 11v?

Does anyone have a detailed DTC list? I can't even find one that lists 46 let alone the detailed conditions in which the codes are set.
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Re: 12P and DTC 46

Postby antus » Sat Aug 10, 2019 12:24 pm

Looking at the code DTC 46 seems to be:

If current MAP is < Baro and Batt volts > 11.1v and there are no reference pulses seen for 2 seconds the engine is assumed running (in module mode) but the ref signal is bad, and then a 46 is set.

So Im not really sure how a bad battery would cause that unless for some reason there is electrical noise on the ref and it doesnt trigger and cranking takes > 2 seconds but its still good enough to be above 11.1v.

Like all these things, when things get weird there are normally more than 1 factor at play at the same time.
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Re: 12P and DTC 46

Postby VK_3800 » Sat Aug 10, 2019 1:17 pm

Thanks guys, I'm pretty certain all the wiring is good as I've re-done most of it and not too keen on getting carried away investigating if its no big deal as everything is very well tucked away! I replaced the dizzy reluctor pickup not too long ago when the original died (after many years of service and abuse), and the ignition module was new when I did the conversion but that's not saying much I guess.

The battery voltage thing is a definite possibility while cranking and the kind of thing I was wondering about, if its something like that falsely triggering the code then its not a concern. Interesting that this code should go away, the check engine light is definitely off yet it still shows when connecting via Tunerpro - I wanted to reset it to see if it comes back again.

I have some spare ECMs that I can try if need be, hopefully not that though as this is the one set up with the comms.

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Re: 12P and DTC 46

Postby vlad01 » Sat Aug 10, 2019 1:46 pm

When my 46 came up. The battery was really flat so it barely turned over. I seem to recall the starter clicked a few times as it only just turned over , but it did fire and came up with the code straight away.

I was thinking that it had some vac signal and voltage was really low and perhaps it was too low for a reliable ref signal for the duration of the cranking but still enough to fire?

Had it happen twice, both upon cranking when the battery was nearly dead and the 46 came up instantly as soon as it fired. I have since kept the battery on charge and haven't had the code come up in 2 years since.
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Re: 12P and DTC 46

Postby pman92 » Sat Aug 10, 2019 7:07 pm

It will set no ref pulses while cranking if battery voltage is below 11v and MAP is below baro I think

So If MAP drops slightly and battery voltage drops below 11v as soon as you start cranking, before it gets past 1 reference pulse (engine barely started turning) due to a weak battery the code will be set
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Re: 12P and DTC 46

Postby vlad01 » Sat Aug 10, 2019 7:13 pm

Yeah that makes sense.
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Re: 12P and DTC 46

Postby VK_3800 » Sat Aug 10, 2019 9:31 pm

Sounds like its probably a non-issue, has been fine again tonight but will keep an eye on it.

No battery issues but the big alternator loads up almost instantly on start (or even when cranking) which was part of the reason I changed the belt setup, so wouldn't be surprised if voltage goes weird momentarily during start. Obviously only 4 pulses per revolution from the dizzy too so I guess that leaves a fair bit of time in between to trigger the fault.

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Re: 12P and DTC 46

Postby VK_3800 » Sun Aug 18, 2019 8:42 am

Well it hasn't missed a beat and the light hasn't come on again, seems like it was a non-issue.

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