***This post will be a short write-up as FYI. It will not be as detailed as most posts.***
This vehicle, 05' Ford F150 5.4, came into the shop with a customer concern of a no crank/no start condition. Let me first give you the details of the complaint history.
The customer stated he had driven the truck as he normally does and parked it in the garage. The truck sat in the garage for a day or two. When he went out the next time to drive it, the truck would not crank over. When he would turn the key to the start position nothing would happen. He checked the battery and it was good.
He and a friend checked out a few fuses and a few other things but could not find the problem.
He called me and had the vehicle hauled to the shop.
When the truck arrived at my shop the battery was down (from the customer trying to start it numerous times); so, first things first, I replaced the battery. It was time to perform some diagnostic tests on this vehicle.
Next, I had an assistant turn the key to the start position and probed the wires at the starter solenoid. I found there was no voltage to the starter solenoid, it had ground all the time.
I then pulled a wiring diagram and checked the pertinent fuses for the starting circuit. All tested good. Next, I used a relay tester and checked the circuitry at the starter relay. I noticed the contacts that normally should show a ground when the key is not in the start position, were showing nothing at all.
The fuses and relays are located behind the kick panel on the right (passenger) side. See the picture below:
Next, I checked the fuses for the PCM and all were good. I had tried communicating with it with my scan tool, but had received an error message for "No Communication".
I then tested the PCM relay and found the problem. The PCM relay was not working. It had power to the relay, but the relay was not internally switching. I bench tested the relay and the first couple of times it tested faulty. I tapped it lightly a few times and it came to life.
In the pictures below is the relay:
I replaced the relay with a new one.
In the pictures below you will see where the relay is located in panel. (It is number 203 on the cover legend.)
Viola, the truck then cranked over and started right up!