Supra common fault - usually misdiagnosed.

[carrier_trained]

Some of you may have seen this fault with supra's, it usually shows up when the unit is cold, or if it has been sitting idle for some time, but also can occour randomly.

Ok, you turn the unit on via cab command, after the self test the buzzer sounds, then the micro brings up the fault light, and cab command screams at you, eng has not even cranked.
The alarm generated is 'ENG OIL', and yes theres definately no oil pressure! cause it ain't runnin'!
Now i know a few of you are going to say the adapter harness(module with resistor and diode in series) is at fault, and yes that maybe it, but also there are a few other things that can cause this fault, like:

Worn out Alternator brushes or faulty regulator, shorted rectifying diodes in alt, rubbed wiring, the 'exec/SP15' wire shorts to the 'MPL3/SP14' and this tells the micro the eng is running, thus the oil alarm.
A bad earth at the Alt can also cause this fault, its one of those faults that stump most people, and yet carrier have never released a bulletin concerning this fault! But it is widely known among dealers.

Enjoy!

[cadwaladr]

yeah had that one worked it out,thought this thing thinks its running? how does it know ahh the alti,logiocal thinking ,good tip

[djbe]

Been there and seen it.

Also seen loads of different fault codes when the MP+ wire has started to break down and corrode.

[CTMarco]

Regardless of the actual defect the reason it does this is because you have more than 5v on MPL3 which is the signal back to the micro to say I'm running. In this mode part of the start mode is skipped as it thinks it's running, 15sec later it checks for oil pressure (normal logic), it doesn't have it (OP switch still open) it so displays Eng Oil.

Wonderful logic!.