QuestionQUESTION: what causes ignition fuse to blow when when turning key? i have replaced connection at starter and had starter tested. when i turn key to on position everything comes on, when i turn to start it blows.
ANSWER: Hi Ronald,
I infer that fuse 8 (20 amp) in the pdc under the hood is what blows. If not tell me otherwise.
That fuse is drawn upon in the run position by the fuel pump and the body computer and several fuses in the fuse box under the dash...all that without blowing.
When you go to the start position the starter motor relay coil is energized as is the transmission control module and the starter motor solenoid switch... plus almost everything else that was powered in the 'run' position. The secondary fuses could each handle up to 10 amp each so you can see that a 20 amp fuse might be overwhelmed by almost anything else drawing too much but not blowing the 10 amp fuse it was powered by.
You could try removing the starter motor relay in the pdc and see whether the fuse then doesn't blow. If it blows then it has to be the transmission controller or the wire to it on pin 8 is shorted to ground. If it doesn't blow, then either the starter relay actuation coil is shorted to ground, or the solenoid switch actuation coil on the starter motor is shorted to ground, or the brown wire from the starter relay socket (the outside-most pin in the socket) to the solenoid switch is shorted to ground or the fuse may just be overwhelmed (see below).
I would try switching out the starter relay with one of the adjacent radiator fan relays as a test of the starter relay. If that avoids the blow out then change the relay. And if that doesn't avoid the blow out, then I would check the resistance to ground of the socket pin with the brown wire disconnected at the solenoid on the starter to see if the wire might be grounded. If the wire isn't grounded then I would suspect the starter solenoid's actuation coil is overdrawing the fuse, which might not show up on a starter motor test (it could work but draw too much current).
I hear of this problem so often that I am tempted to suggest trying a 30 amp fuse in place of the 20... it may just be too close to being blown. It would still blow if there was a dead short so it aught to be safe to try that.
Please let me know what you learn.
Roland
PS Please 'rate' my answer and also consider giving me a nomination to be 'expert of the month. Thanks
---------- FOLLOW-UP ----------
QUESTION: i replaced #8 fuse with a 30 amp and it does not blow fuse anymore but engine will not turn over. am going to check some other suggestions u made. what do u think about the fuse not blowing now. i also took brown wire off starter and it would not blow a 20 amp but when i put it back on it blew the 20 again
ANSWER: Hi Ronald,
It appears to me that the brown wire is ok, and that the starter solenoid switch is probably causing the fuse to blow and that it is not closing the switch which is required to send current from the battery to the starter motor coils. So I would believe that solenoid, paricularly if it doesn't click, is the cause of both the fuse and the starter not responding. The starter 'test' may not have actually been done via the solenoid but rather by-passed it.
Thanks for the report. But do switch out the starter motor relay as it could be causing the smaller fuse to blow and also not closing its points which would explain the no action at the solenoid switch (do you feel/hear it click when the starter is tried?)
Roland
PS Thanks for the rating and nomination.
---------- FOLLOW-UP ----------
QUESTION: which is starter motor relay..it really isnt telling me on vehicle.only thing i see as far as starter on pdc is #8 fuse for starter ignition fuel pump.. also if no click heard or felt i should replace selenoid because that would most likely be issue?
AnswerHi Ronald,
The starter relay is the front/outside-most of the 4 relays in the very rear of the pdc, which is a step-down area behind the front of the box*. If the relay is substituted (use either relay in the very back of the box which are for the radiator fan speeds), and it clicks softly when the key is tried, then if the solenoid on the motor doesn't click loudly I would have to believe that the solenoid on the motor is bad.
Roland
PS Thanks for the rating and nomination. By the way, you can do it again :)
* To access the 4 relays, remove the air intake housing and resonator which hides that rear section of the box
