Monday, June 20, 2011

Honda crx blows ecu fuse when main relay is plugged?

If the car simply died like someone throwing a switch it is probably a blown fuse to the ECU which shuts down the injectors and the distributor on the 88-91 crx.. Power for those systems comes from the ECU and loss of either one or both will kill the engine instantly.----------------

The fuse for the ecu is in the main fuse box in the engine bay called the HAZZARD fuse. remove this for 10 seconds to clear the codes and try again if the fuse isn't blown.
please note there are two fuses.

Yes there are two fuses (circuits) that supply power to the ECU. One is always hot for the ECU memory (10A) and this is the fuse which you pull to clear the codes, the other is through the main power relay (15A) and its only powered when the ignition is on. The ignition switch circuit powers the injectors and the igniter through the ECU which you don't want ON all the time or you will kill the battery. If it is a fuse, my guess is the (15A) on the main relay circuit and not the one you pull to clear the codes.-------- Remove both fuses and wait for 10 seconds, then reinsert and see.--------
Also where you connect the relay.Clean that terminals too and see if its blowing the fuse again.

One of our user who faced the same problem, tried this:---

"I checked all the grounds and wiring for shorts or open wires, could not find anything. I'm guessing the problem might be in the fuse box itself?"

I took off the fuse box, replaced fuses. Connected the wires one at a time to see at what point it blows. The battery wire went on, then the wire to the alternator. Fuse is still good. Then there are the 3 wires on the other side, the one closest to the battery/alternator wires went on, then i put the middle of the three on and the fuse popped.

Look at the wires for the 02 sensor, they are probabbly grounding out on the exhaust or I/M bracket.

I have a 4 wire o2 harness and it's pretty long, might have pulled down a bit. I'll have a look at that tonight.

i could see a cable that was shorting the fuse , obviously mealted. That's what must be shorting it out.
I replaced the 02 sensor wires and that helped me.I just connected one external wire.--------And that solved my problem.----------

This is what our user did.---------
There is possibility, that some of the wires got loose or getting shorted or got cut in between.This is causing the fuse to blow.----------------

The procedure and working system of ecu fuse and relay is as follows

3 relays in one located under the drivers side dash above the hood release. When the ignition is turned on it supplies power to the Dashboard/radio circuit, the fuel pump circuit, and the ECU/injectors/igniter circuit. You can hear the fuel pump running, it is obvious if the radio does not work or the dashboard does not light up, it is not so obvious if the injectors are not firing or the igniter igniting because the car will crank...it just won't start. All the fuses can check out OK but if the ECU (15A) circuit is not powered by the main power relay...it won't start.-----------
In your case the main relay is new and replaced and both fuses are working then it can be faulty ECU.There is short in ECU.It can cause this problem.Read as follows:----
Now with the main realy removed the fuse does not blow, as soon as I hook the relay up the fuse blows. I decided to take my ecu out to see if anything was wrong with it. When I opened it up I got the worst smelling thing i've ever smelled. I noticed this one piece, might be a resistor idk. The thing looks completely burnt and melted.

Its a diode.A diode is like a one way gate, power can pass in one direction and ground in the other direction.

I replace the diode, but did not helped, so i replace the ecu.I ordered it from local auto part store.It took one week for them to get me the replacement ecu.I connected the new ecu, but still my car will not start.So i disconnected the battery for 30 minutes and then connected the car starter in first click and still running fine.

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