VT SUPER6 - No 3x or 18x signal but cannot see fault codes?

Holden/Delco Tuning. ALDL, OBD 1.5. Circa 1989 to 2004.
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VT SUPER6 - No 3x or 18x signal but cannot see fault codes?

Post by UnknownSoldier »

Hi all, hoping for some help.. plenty of issues at the moment as I can't start the car (no spark)
I got hold of an aldl and diagnostic software and was shown that the pcm isn't receiving either of the CAS signals.. I will investigate this itself but was mainly wondering why, when I try to enter manual fault code mode via the 5 &6 plug bridge, do I get a solid engine only light and no code flashing ? Even the diagnostic software in using shows no codes.. I would have thought I should at the very least be logging a 47 error.. it's worrying me the pcm has some other faults
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Re: VT SUPER6 - No 3x or 18x signal but cannot see fault cod

Post by pman92 »

If there's no ref pulses then it's as if the engine isn't turning to the PCM.
If it set DTC 47 every time there was no pulses, then it would be logged every time you turned the ignition on.
To set DTC 47 the engine has to be running and it has to receive X number of ref pulses without seeing a 18x pulse.
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Re: VT SUPER6 - No 3x or 18x signal but cannot see fault cod

Post by UnknownSoldier »

Thanks for clarifying.

That being said, the diagnostics is showing 3x present and 18x both with the value NO

should the pcm be receiving some signal even in off/idle stage ? Otherwise I assume you get this flag... I do think I have a fault somewhere in that line so I'll be trying to narrow it down over the weekend, either the CAS isn't getting power, it's not outputting signal to the dfi, or the dfi signal out isnt making it to the pcm..
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Re: VT SUPER6 - No 3x or 18x signal but cannot see fault cod

Post by charlay86 »

If the CEL on dash isn't flashing out a code 12 (no error) when you bridge diagnostic mode pins then the PCM isn't communicating over the serial bus to the dash.
Very likely you have an issue with another module on the serial bus that is preventing communications from happening.
This will give you a no start condition because the pcm can't get through to the BCM for vats.
I would start by disconnecting other modules from the ALDL bus like the ABS etc.
Any welding on the car recently..?
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Re: VT SUPER6 - No 3x or 18x signal but cannot see fault cod

Post by UnknownSoldier »

charlay86 wrote:If the CEL on dash isn't flashing out a code 12 (no error) when you bridge diagnostic mode pins then the PCM isn't communicating over the serial bus to the dash.
Very likely you have an issue with another module on the serial bus that is preventing communications from happening.
This will give you a no start condition because the pcm can't get through to the BCM for vats.
I would start by disconnecting other modules from the ALDL bus like the ABS etc.
Any welding on the car recently..?
Thanks mate. No welding i am aware of.
What's weird is it does seem to be communicating, at least via other means.. Ive got an aldl and an old copy of envious customs diagnostics . See attached photo, I am getting data from the pcm via this method.. although nothing when doing the manual pin bridge.. and even this reports no fault codes but I can at least monitor some items.. can you please run your eyes over and see what you think?
Fyi I have back probed the 18x CAS wire in to the pcm and it is indeed 5v.. but showing no reading on the diagnostic.. plus the car is behaving real weird like unlocking the boot when I turn the ignition off ?? all these things are making me think a serious pcm issue ..
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charlay86
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Re: VT SUPER6 - No 3x or 18x signal but cannot see fault cod

Post by charlay86 »

Unlocking the boot would be a BCM problem, the PCM has nothing to do with that.
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Re: VT SUPER6 - No 3x or 18x signal but cannot see fault cod

Post by charlay86 »

Also there are no other means of communications, aldl bus is it.
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Re: VT SUPER6 - No 3x or 18x signal but cannot see fault cod

Post by Charlescrown »

Why not get a multimeter and do some simple testing. + - and 3X and 18X outputs on the 4 wires going to the plug.
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Re: VT SUPER6 - No 3x or 18x signal but cannot see fault cod

Post by antus »

if the boot is triggered from the bcm and keyoff opens it then it sounds like the bcm might be faulty. if this is the case that could not transmit the bus heartbeat and cause a whole bunch of problems, even if the pcm is healthy. if thats it you'd need to replace the bcm and do a vats relearn, or disable vats in the pcm. if you have tuning tools you could turn vats off in the pcm, disconnect the bcm and then see if it starts at least. ive also heard the abs module tends to die and knock out the bus, so that might be another good module to disconnect first.
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Re: VT SUPER6 - No 3x or 18x signal but cannot see fault cod

Post by Charlescrown »

Just had a thought. VT had an issue when the ABS module failed it pulled all the diagnostics down. Can't remember if it also affected the engine running but try unplugging the ABS module and see what happens.
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