He wouldn't be getting a code 12 if the ECM didn't have power.
Check for fuel pressure. Should be around 38-48 psi cranking. If you don't have a fuel pressure gauge..... just remove the air inlet to the throttle body and spray some flammable carb spray down the throat of the throttle body and see if the motor wants to light off. That right there will tell you if it's a fuel delivery or something else problem.
If the motor still does nothing...... Pull one of the plug wires at the spark plug as use a spark tester or a small screwdriver pushed into the end and hold it 1" away from a good ground and see if you have spark at the plugs. Check a couple of plugs just for good measure. If that's ok...... get a 12v test light then remove one of the injector connectors and with someone cranking the motor, see if you have a continuous light on one of the terminals. If that's ok, then take your test light ground clamp and move it to a positive 12dc power source and check the other terminal in the injector connector for a "pulse" or "signal" to the injector. In other words, your test light should "flash" when the engine is cranked. That tells you that the ECM is trying to ground the injector getting it to fire.
Now... if you didn't have the continuous 12v on the 1st test at the injector with your test light hooked to ground... then use a volt meter and unplug the TPS and check for 5v at one of the terminals with the key on. If you don't have 5v at the TPS connector, you've either lost power to the ECM or the 5v reference is grounded or dead coming out of the ECM and then you'll have to find out if it's the ECM itself or a circuit/sensor grounded.
