2003 3.4L Crank No Start 7.5a Ignition Fuse Blows

Hello,

I have recently purchased a 2003 Toyota Tacoma with a 3.4L V6. The truck is in overall great shape, however the previous owner had parked it for some time and when going to start the truck to show me functionality before purchase we could never get it to fire. Item worth noting is the battery was very dead as it had sat for 3 years, the last 2 of them continuous in a garage with no run time. At this point in time a marine type charger/tender(recall it having odd voltage) was installed before I showed up with a new battery. The owner and I came to an agreement and I bought the truck at a slightly lower price than originally agreed upon.

Once the new battery was installed the truck would crank very well, however it wouldn't do as much as stumble(the farmer in me even tried ether to rule out fueling issues). Since then I found that the ignition fuse was blowing as soon as the key was turned to run/start positions. After doing some digging on AllData (electronics end is not my forte) I found that the 7.5A IGN Fuse powers the fuel pump as well as two feed wires to the ECM. Contrary to most locations of the OCR(open circuit relay) I believe to have found mine located at the bottom right side of the fuse block located behind the panel of your left knee. Unplugging this has not stopped the fuse from blowing instantly. I then moved onto the ECM. I started off by unplugging all of the connectors, for the first time the fuse did not blow when the ignition switch was turned to run/start positions. I started plugging the connectors back in and as long as the far right connector is unplugged the fuse will not blow. I believe this connector to be E5. However this is where I hit a bit of a wall as far as diagnostic abilities with electronics, as well as the resources I have found to help support that task.

What I don't want to do is spend $300+ for an ECM that doesn't fix my issue. But I also don't know how to properly test wires on the connector or pins on the ECM for a short. As in the ECM is fed power with 2 BLK/WHT wires, but what wires coming out can have a negative affect on those feeds and blow the fuse?

Any diagnostic diagrams that could be shared, locations of connectors that are fed from the ECM(powered by the two BLK/WHT feeds) or any input at all to help solve this issue would be greatly appreciated. As well if any further detail is needed from my end please let me know and I will do my best to help provide that information.

 

Looking at the diagrams The only thing that I see that could be shorted that the ECM powers is something in the EFI Relay control circuit. The only other thing the ECM powers is the electronic throttle control motor if you have ETCS but I believe it uses the 20A feed from the EFI relay for that power source.

 

DM93,

Thank you for the response. Based on that would you agree that if I were to pull the relay/fuses for the EFI circuit and still have an issue it would be something internally wrong with the ECM?

 

I would test the EFI relay control circuit and Throttle Motor control circuits for a short to ground before replacing the PCM, the best method to do that would probably be to unplug them and the PCM, find the wires at the PCM, and put an ohm meter between each wire and ground.

 

Hey did you ever figure out what was wrong, I have a 2002 with the same problem. Not sure if I should buy new ecu or if the problem is elsewhere.

 

If you start popping fuses around the ignition system.....
always suspect the ignition switch first......rule it out....

runs good when cold......but wig out under load......

of course after checking battery and grounds.....

other systems/sensors down line.... if they're oem toyota are pretty tough.....
unless they're 25yrs old and wore out.....


anything non oem touching the motor.....do yourself a favor and get rid of it sooner than later.....