2020 shortcut to fix NO Communication bus wiring problems for 2004 Mazda vehicles!

2004 Mazda Bus Wiring Network

Shown below is a 2004 Mazda bus wiring diagram for the DLC connector. To test NO COMMUNICATION fault message from your scanner, you can use this diagram as your guide. Using a digital voltmeter, you can fix problems like no start, intermittent shorts by measuring the voltages shown in the DLC pin terminals.

2004 Mazda Bus wiring network

Note: This 2004 Mazda data bus wiring above has CAN high and Lo (hi speed) bus wires at DLC terminals pin 6 and pin 14 respectively. There is also a low speed bus wire (K-Line) at pin 7. These pins at DLC can be easily diagnosed using a voltmeter in minutes! 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.

2004 Mazda bus wiring test

2004 Data Bus Network Description:

Looking at the 16 pin terminals of the DLC, there are basically 3 pins to worry about:

PIN 6 which is the CAN Hi speed bus communication signal. When you measure it it with a voltmeter using PIN 5 as your ground, you should get 2.5 volts at key on engine off (KOEO). Take note that this voltage reading actually fluctuates between 2.5 volts to 3.5 volts at KOEO.

PIN 7 which is the K Line bus communication signal. This is a low speed bus signal and usually is a lone wire going to the accessory modules like ABS and Airbag as shown on right. When testing for voltage, probe PIN 7 against PIN 5 and you should get about 5-7 volts st KOEO. If out of range, disconnect the 3 modules one at a time; ECM, Air bag and ABS modules.

PIN 14 is the High Lo bus communication signal. This bus is paired together with the CAN Hi bus wires which are twisted together. To measure the voltage of this bus at PIN 14, probe this pin against PIN 5 and you should get 2.5 volts average reading at KOEO. This voltage is also fluctuating between 1.5 volts to 2.5 volts.

Troubleshooting 2003 VW data bus network:

Looking at the diagram, you can see the CAN bus wires (both CAN Hi and CAN Lo) entering the TCM and Display control unit. These modules act as a gateway module which feed to all the modules except the modules under the BCM and Unified meter amplifier module that feeds the instrument cluster. So if we are to check which module is defective, we can measure the resistance (60 ohms) between PIN 6 and PIN 14 with battery disconnected. Isolate the BCM module by disconnecting it at 3 black dots that connects to its pins: Can H, Can L and the serial link.

I usually verify the ECM by going straight to the sensor like crank sensor to check for presence of 8 volt supply at the sensor. You can also measure the 5 volt vref supply at TPS sensor if easy to access.

NOTES:

1.) The actual bus network diagram will show you the exact colors of the bus wires and locations of the modules in the circuit.

2.) Above DLC diagram can be used for 2004-2006 Mazda models. The only difference is the number of modules being used on later models. Also, the TCM is used all the time as a gateway module for testing purposes.

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