Hi ramaillet. Welcome to the forum. You should expect to find about five or six other blown fuses. Look inside the car and under the hood. The Engine Computer has protection built in for reverse polarity. To start with, listen for the hum from the fuel pump when you first turn on the ignition switch. It should run for one second, then turn off.
When you turn on the ignition switch, the engine computer turns on the Automatic Shutdown (ASD) relay for one second, then it turns back off until pulses arrive from the crankshaft and camshaft position sensors. These pulses only occur when the engine is rotating, (cranking or running). It looks like the computer isn't turning on the ASD relay if you're troubleshooting the system while just leaving the ignition switch turned on, but that's what's supposed to happen. That one-second that the relay turns on is enough to run the fuel pump to insure fuel pressure is up and ready to start.
When crankshaft sensor pulses arrive during cranking, the engine computer turns on the ASD relay constantly. Voltage from the relay feeds 12 volts to the ignition coil(s), fuel injector(s), alternator field winding, oxygen sensor heater, and the fuel pump or fuel pump relay.
Since you've already determined spark and fuel are missing, and reverse polarity should not have made it to the two sensors, strongly suspect another blown fuse before you condemn the computer. The clue will be if the fuel pump does not run for that one second. As an alternative, you can measure the voltage on the dark green / orange stripe wire at the coil pack or alternator field. If you DO have voltage there for the first second, (and the pump runs for that one second), but not again during cranking, then suspect a defective sensor.
Another clue of a defective Engine Computer, after you've checked the fuses, is if the Check Engine light does not turn on for the few-second bulb test when you turn on the ignition switch.
Caradiodoc
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Tuesday, May 4th, 2010 AT 1:24 PM
