2003 Ford F150 network protocol is an example of multiplex networking. Now I will show you how to check NO COMMUNICATION problems when this message is displayed in your scanner by using cheap tools like the common voltmeter. Shown below is a typical computer data bus diagram.
2003 Ford vehicles use low speed bus wires from DLC terminals: pin 2 shown as blue wires, pin 7 yellow wires, pn 10 green wires and pin 13 violet wires. They all connect to their respective modules shown in boxes. You can get this exact wiring diagram from your local parts stores or get it online from ATS.
Note before using these diagrams:
1.) I made these diagrams to show how 2003 FORD F150 data bus circuit are wired together with the DLC. This is an approximate diagram to simplify it.
2.) From the conception of OBD2 in 1995 upto 2002, most electronic circuits were controlled mainly by power control module (PCM) alongside the body control module (or called GEM module by Ford). This method required a lot of wiring harness between those two modules including the sensors and other body parts. SOLUTON? Use numerous modules or multiplex grouped together as shown above. This design NOT only save costs but it allows cheaper upgrades by merely adding new modules to the circuit.
2003-2004 F150 DLC Diagram Description:
Looking at the diagram above, you will see how the DLC of your 2003 Ford F150 vehicle is wired to the following modules starting on the right:
Power Train Module (PCM) is wired by 3 data bus wires thru Pin 13, Pin 10
and Pin 2. Please take a good look on connector links S3 that came from
Pin 10 and connector link S1 that came with Pin 2. You will need this
links when troubleshooting the wirings if you need to isolate the PCM circuit.
Cluster Module is the instrument cluster module which has 2 data bus wires only; Pin 10 and Pin 2.
Temp Module is the climate control module and has 2 data bus wires similar to Cluster Module above it.
GEM Module is Ford's equivalent to GM Body control module although not as active the GM counterpart. It is fed by a single wire thru Pin 7 via S2
Security Module can be compared to GM's anti theft module but is wired also thru Pin 7/S2 connector link.
The same single wire set up is also made on the 3 other modules below namely ABS, Seat (restraint) Module and Timer Module.
What is important here is knowing how to identify each module and how they are connected by data bus wires so we can diagnose it.
It is worth mentioning that you only need a
voltmeter and a cheap scanner to find Ford NO COMMUNICATION issues. Please
remember that the voltage of these Pins 2, 7, 10 and 13 can vary between
5 to 7 volts at key on engine off (KOEO).
Troubleshooting intermittent NO COMMUNICATION problem using this 2003 Ford 150 data bus protocol.
Looking at DLC connection terminals, the main players to run your engine are Pin 2, Pin 10 and Pin 13. If you have a NO START and NO communication after you
scanned the DCL, you have 3 main modules to deal with: PCM, Cluster
Module and Temp modules. In the actual data bus wiring diagram of the
vehicle, you can see the color of the wires and the location of the 3 modules including the S3 connector links so you can test them at KOEO and during idle.
With your voltmeter hooked up at Pin 2 at KOEO, lets say your reading is 3 volts. This means the data bus voltage is being pulled down by a short to the ground. Normal reading should be 5.0 v at KOEO.
PCM module runs your engine and if you disconnect the Cluster and Temp
module one of the time while watching your voltage reading at Pin2, you
will know if the problem occurred on those 2 modules. If the engine starts
and communication is restored and reading went up to 5 volts at KOEO,
then we isolated the problem. It is either one of the 2 modules and you can plug it
one at a time until the voltage is pulled down again to confirm.
What happened if the PCM is the one shorted itself? If unplugging it will restore the voltage reading at Pin 2 then we know we can check that by
going to the PCM itself to check the sensors, reference voltage, power and ground distribution wiring diagram
to determine if any of the wire is shorted.
If NO COMMUNICATION is caused by any of the 5 modules on the left, we
know we can easily isolate it by disconnecting the circuit at S2 and
watch for the Pin 2 voltage reading if it returns to 5 volts.
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