Help finding transistor for PCM

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09-10-2018, 09:40 PM

DrWizard

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Help finding transistor for PCM

I am trying to cross reference a transistor inside a Ford PCM...

The PCM is a 3L5A-12A650-GC aka MP2-111, from a 2003 Ford Ranger 3.0L 6 Cyl Flex Fuel.
The manufacturer logo on the old transistor is for On Semiconductor.
The part number on it is J112.
It was manufactured in 2002.
It drives the fuel vapor purge solenoid valve, part of emissions control.
Its on the corner of the board, away from the connector / towards the passenger. Holding the PCM with the board face up and the connector towards the bottom, it is on the top left corner.
Thus, a 12 volt inductive load. Dunno how much current, but probably not more than a couple amps and probably not that much.
It uses PWM to quickly pulse the solenoid to effectively give analog control over the amount of vacuum let thru.
The solenoid was shorted, which damaged the transistor (although not visibly burnt)
On Semi J112 currently refers to a JFET in a TO-92 style case.
But the old one is in a TO-252 style case.
Did On Semi produce J112 JFETs in a TO-252 style case in 2002, at least for Ford?
The PCM is only supposed to turn it on under a certain complicated set of conditions making debugging all the more difficult. Live testing is out of the question.
I hooked up an LED to the output and duct taped it to the windshield so I could monitor whether or not it is working while driving.
I replaced it with an On Semi MJD112G Darlington Power Transistor, and the LED flickered on and off pretty much as/when expected, but only with the solenoid disconnected/unplugged.
With the solenoid connected, it won't come on unless you momentarily ground the output.
I replaced it with an On Semi MTD3055VL N-Channel Logic Level Enhancement Mode FET but that didn't work. The LED does not come on at all.
I am assuming the transistor is receiving a proper control signal to the gate. Again, due to location, there is no real way to test this, but considering why it failed to begin with, and that it partially works with a darlington, I'm reasonably sure it is getting a signal from the microcontroller.
A refurbished PCM is $127 with shipping. I could live with that. They even reprogram it with VIN number, engine parameters, etc.
But the PCM also controls the anti-theft system with the PATS keys, and they need to be programmed to the replacement PCM as well. The PCM refurb-er can't/won't do that. The dealerships won't do that for a 2003 anymore. Have to get a locksmith. No such thing as a locksmith shop anymore, can only find mobile locksmiths. Cheapest I can find is $300.
Therefore, this transistor is effectively worth $427.
The truck runs OK without it. But I am trying to be a good eco-citizen and not pollute with fuel vapors. But not for $427 in addition to what I've already spent getting this far. Not to mention the annoying "Check Engine" and "Fuel Cap Leak" lights stay on.