This 2003 Toyota Tacoma network protocol DLC diagram is an example of multiplex networking for imports. This will show you how to check NO COMMUNICATION problems when this message shows up in your scanner. Most people thinks it is a difficult problem that would need a garage to see it. But you can fix it in a couple of hours using a voltmeter.
This 2003 Toyota bus wirings above looks similar to Ford or Dodge bus wires. However, during troubleshooting, all you care is to check the voltage at DLC pin terminals like power shown in red, blue is ground and the bus wires connected to the PCM.
These bus wires are low speed network circuit and will read 5-7 volts at KOEO (mostly 5 volts). For more details, you can get this exact wiring diagram with correct wire colors and pin connections from your local parts stores or get it online from ATS with one on one assistance.
1.) I made this diagram myself to show how 2003 Toyota Tacoma data bus circuit is wired together with the DLC. This is only an approximate diagram as I see it. I don't profess that all of these information are correct but in case you find some errors, please contact me at my ATS homepage.
2.) When your 2003 Toyota Tacoma has NO COMMUNICATION problem during scans, it means one of the data bus wires is shorted or one of the module or it's circuit is defective. Symptoms includes NO START, intermittent issues like stalling, occasional cutting out, etc. and no amount of scanning can help you find the problem. This diagram will show you how top mechanics are doing it.
2003 Toyota Tacoma DLC Diagram Description:
Above is a typical 2003 Toyota Tacoma data bus network diagram to the DLC. As you can see, there are numerous data link wires connected to the DLC to various sensor, electronic igniter, instrument cluster, junction boxes circuits, fuses and ECM Module. Just looking at this diagam is very confusing but when it comes to troubleshooting NO COMMUNICATION problem on this vehicle, there are only 6 DLC terminal pins you have to worry about besides DLC terminal Pin 16 (power supply) and DLC ground Pins 4 and 5.
Note: Don't get confused with data bus terms here. Just read on and take a look at the modules/components shown in the boxes and the DLC terminal pins described.
DLC terminal Pin 6 is a LA shared data bus signal going to Airbag sensor assembly that also control SRS light signal at Combination Meter. Inside this module, both TC and SIL data bus signals worked with TS data bus signal.
DLC terminal Pin 7 is a D/G shared data bus signal that goes to ABS Actuator Module. Inside this module, both TC and TS data bus signals worked with D/G data bus signal. DLC terminal Pin 7 also has an extension wire that connects to Junction 11 C to link data bus signals to Air Bag Sensor and Cruise Light bulb of the Combination Meter.
Pin 9 is a TAC data bus signal which goes directly with ECM Module. Inside this module, this signal is combined with WFSE, TC and SIL data bus signals to collect, transmit data including acting as a gate way module for the whole circuit. The Combination meter (another word for Instrument Cluster) also acts as a hub module like the ECM Module.
Pin 13 carries a shared TC signal data bus which links ABS Actuator, ECM, Cruise Control including Air Bag sensor via Junction Box 11 B.
Pin 14 carries a TS shared data bus signal inside ABS Actuator which also carries both TC and D/G data bus signals.
Pin 15 is a WFSE data bus signal that goes to the top of the ECM module on the left. However, it also shares 3 other signals inside the ECM Module.
If still confused, don't concern yourself with all these types of signals except to know the voltage values at the DLC terminal pins at key on engine off (KOEO). The actual wiring diagram will show you the actual lay out of the specific data bus signal mentioned here including the wire colors and the circuit connection to the rest of the data bus links.
Troubleshooting No Communication on 2003 Toyota Tacoma data bus wires:
The main technique of troubleshooting for this type of vehicle is learning how to isolate each of the data bus signals or modules to determine which data bus wire is shorted that will cause NO COMMUNICATION. When testing , measure the voltage reading to the DLC pin terminals one at a time. Using the same voltmeter voltage setting (5 volts at KOEO) we used for testing 2003 GM, Ford and Chrysler vehicle problems, disconnect each of the modules to determine which DLC terminal pin voltage is out of range.
Example, hooking the voltmeter negative lead to DLC Pin 5 ground pin terminal, probe DLC Pin 6 terminal using the voltmeter positive lead connection. If the voltage reading is 2 volts higher or lower than 5 volts at KOEO, we know the problem is mainly Air Bag Sensor which we can isolate by disconnecting the 3 Green dots connections at the Air Bag Sensor.
We can also double check our voltage reading by isolating this Air Bag Sensor by disconnecting the same 3 wires thru data bus connector 1 at Junction Box 3 shown in red number color, Junction Box 11 C data bus connector 5 (shown in red number) and finally Junction Box 11 B data bus connector 7 (shown in red number).
If voltage reading goes back to normal reading (5 V) at KOEO, then we can conclude the Air Bag Sensor/circuit wire is faulty.
The same test can be done when isolating the ECM Module by disconnecting all it's red dots connectors inside the ECM Module. To verify voltage readings, disconnect the black dot 4 in Junction Box 11 C and red dot VT beside the ECM Module. If voltage reading is out of range when testing Pins 9, 13, 14 and 15 at DLC and isolating the ECM Module makes it goes back to normal (5 V), the problem is the ECM/circuit wirings.
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