The manufacturer logo the old one is On Semiconductor.
It was manufactured in 2002.
The part number on it is J112.
It is in the PCM (computer) of a 2003 Ford truck.
It drives a vacuum solenoid valve. (The fuel vapor purge valve, part of emissions control)
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 case.
But the old one is in a TO-252 case.
Did On Semi produce J112 JFETs in a TO-252 case in 2002, at least for Ford?
Of course (Murphy's law) it is difficult to access, and impossible to access while connected and the engine is running. Live testing is out of the question.
Furthermore, the PCM is only supposed to turn it on under a certain complicated set of conditions making debugging all the more difficult.
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. 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 RFID keys, and they need to be programmed to the replacement PCM as well. The PCM refurb-er won't/can't do that. The dealerships won't do that on 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.
Oh man -- my sympathy (and admiration for taking this on!)
Have you thought about getting an entire module from a used parts dealer and pulling the one transistor you need out of it? Or pulling the module from a scrapped truck in a yard somewhere?
The only other idea I can think of is contacting Ford. I'm guessing the part number is proprietary to the module manufacturer. Someone at Ford might be able to help if they're having a good day.
Would like to hear how you solve this. My score fixing cars is zero.
Auto Makers will often buy enough parts from suppliers that the supplier will mark the parts with "house numbers" meaning that the the part number only makes sense to "FORD" and the specifications and original part number are really only known to THEM and the SUPPLIER. With a name like J112, even though ON SEMI makes one with that name, its highly likely its a house part based on he mismatch of cases used.
Auto designs are notorious for using high-side drivers so inserting an N-Channel Device where a P-Channel device is needed might also be related to your lack of success. (But that's a wild guess and I assume your LED test resolved that concern)
One side of the solenoid connects to +12v (ignition) the other side goes to the computer, so it is a N-Channel. DC resistance of the solenoid is 64 ohms, so it draws less 1/4 amp, although being inductive it has an inrush current, and as noted the computer rapidly pulses the solenoid. No (obvious) diode on the circuit board, there may be one inside the solenoid housing.
I probably will end up getting another used PCM and cannibalizing it for parts, although even that will cost me $50. (Better than 400!). Problem is there are at least 40 different versions, sub-versions, and revisions to this model of PCM. I would expect that most all of them use that same transistor for that function, and that it hopefully is in the same location on the board. There are about a dozen power transistors, most of them the same, but the one in question here is the only one marked J112. A couple of years ago I swapped out an IGBT transistor, that one I was able to cross reference without difficulty.
According to users on the Ford forums, schematics and parts for the PCM are not available to anyone at any price. Ford expects youthe dealer to swap out the entire PCM and do all the reprogramming. I should also note that there are absolutely no markings on the board, not even R1, R2, R3, C1, C2, D1... etc. The board also has some sort of silicone conformal coating, although not very thick and easily scraped off.
I'm not that familiar with the Fords but the system you are working on sounds like the fuel tank leak detector system. This sounds like the older type system, I don't know when Ford changed to natural decay type.
Typically the valve would operate when the car is not running and relatively thermally stable (often at night). When it runs is limited by a number of factors in addition to the above. For instance the amount of fuel in the tank i.e. it will not run the test if the fuel is <1/3 or up near full.
The system works by pulling a vacuum on the tank, closing the valve and waiting for the pressure to decay. It will perform this test numerous times before actually causing a MIL code (check engine or fuel cap).
Often on ECM output drivers, the output device will tell the ECM if there is current being drawn (for fault testing). This takes more that 3 pins. How many pins does the failed device have? Or if the current test is on the board, are you returning your output FET to the same place as the failed device?