That sheds a new light on the story. A simple trick to finding a short is to replace the blown fuse with a pair of spade terminals, then use small jumper wires to connect them to a 12 volt light bulb. A brake light bulb works well. When the circuit is live and the short is present, the bulb will be full brightness and hot so be sure it's not laying on the carpet or against a plastic door panel. Now you can unplug electrical connectors and move things around to see what makes the short go away. When it does, the bulb will get dim or go out.
There's an additional clinker in this circuit. The automatic shutdown relay turns on for one second after turning on the ignition switch, which obviously isn't enough time to troubleshoot anything. It turns on again whenever there's engine rotation, meaning cranking or running, and again, it's not practical to run the starter as long as it takes to diagnose the problem. The light bulb will still limit current to a safe level, but to energize the circuit for testing, the easiest is to remove the ASD relay and install a jumper wire, then you can troubleshoot the circuit without even turning on the ignition switch. Depending on which style of relay you have, jump terminals 30 and 87 together or the two with arrows in my sad drawing below.
The ASD relay feeds the ignition coil, injectors, alternator field, fuel pump or pump relay, and the oxygen sensor heaters. The most common cause of blown fuses is a wiring harness to the oxygen sensors fell down onto hot exhaust parts, melted, and the heater wire is grounded.
Saturday, June 21st, 2014 AT 12:12 AM