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Free to use workshop manual for your 2015+ Mk4 'ND' Mazda MX-5

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DTC: 28:Er09 [AUDIO UNIT]

Description	No USB playback function file/track
Detection condition	When USB device connected, connection error detected. When USB device connected, audio unit internal malfunction detected. When USB device connected, read error detected.
Fail-safe	Not applicable
Possible cause	USB device malfunction Incompatible USB device (format) used Auxiliary jack/USB port connector or terminal malfunction Auxiliary jack/USB port malfunction Audio unit connector or terminal malfunction Short to ground in wiring harness between the following terminals: Audio unit terminal 3C—Auxiliary jack/USB port terminal UA Audio unit terminal 3B—Auxiliary jack/USB port terminal UC Audio unit terminal 3D—Auxiliary jack/USB port terminal UB Audio unit terminal 3A—Auxiliary jack/USB port terminal UD Open circuit in wiring harness between the following terminals: Audio unit terminal 3C—Auxiliary jack/USB port terminal UA Audio unit terminal 3B—Auxiliary jack/USB port terminal UC Audio unit terminal 3D—Auxiliary jack/USB port terminal UB Audio unit terminal 3A—Auxiliary jack/USB port terminal UD Audio unit malfunction

Diagnostic Procedure

Step	Inspection		Action
1	VERIFY IF MALFUNCTIONING LOCATION IS USB DEVICE After obtaining the customer's consent, connect a normal USB device that was not used when the malfunction occurred. Is the connection detected?	Yes	System is normal. (Explain to the customer that there is a malfunction in the USB device which was used or a malfunction occurred due to use of an incompatible USB device (format).)
		No	Go to the next step.
2	INSPECT AUXILIARY JACK/USB PORT CONNECTOR CONDITION Switch the ignition off. Disconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Disconnect the auxiliary jack/USB port connector. Inspect the connector engagement and connection condition and inspect the terminals for damage, deformation, corrosion, or disconnection. Is the connector normal?	Yes	Go to the next step.
		No	Repair or replace the connector, then go to Step 7.
3	INSPECT AUXILIARY JACK/USB PORT Inspect the auxiliary jack/USB port. (See AUXILIARY JACK/USB PORT INSPECTION.) Is the auxiliary jack/USB port normal?	Yes	Go to the next step.
		No	Replace the auxiliary jack/USB port, then go to Step 7. (See AUXILIARY JACK/USB PORT REMOVAL/INSTALLATION.)
4	INSPECT AUDIO UNIT CONNECTOR CONDITION Disconnect the audio unit connector. Inspect the connector engagement and connection condition and inspect the terminals for damage, deformation, corrosion, or disconnection. Is the connector normal?	Yes	Go to the next step.
		No	Repair or replace the connector, then go to Step 7.
5	INSPECT WIRING HARNESS BETWEEN AUDIO UNIT AND AUXILIARY JACK/USB PORT FOR SHORT TO GROUND Verify that the auxiliary jack/USB port and audio unit connectors are disconnected. Inspect for continuity between the following terminals (wiring harness-side) and body ground: Auxiliary jack/USB port terminal UA Auxiliary jack/USB port terminal UC Auxiliary jack/USB port terminal UB Auxiliary jack/USB port terminal UD Is there continuity?	Yes	Refer to the wiring diagram and verify whether or not there is a common connector between the following terminals: Audio unit terminal 3C—Auxiliary jack/USB port terminal UA Audio unit terminal 3B—Auxiliary jack/USB port terminal UC Audio unit terminal 3D—Auxiliary jack/USB port terminal UB Audio unit terminal 3A—Auxiliary jack/USB port terminal UD If there is a common connector: Determine the malfunctioning part by inspecting the common connector and the terminal for corrosion, damage, or pin disconnection, and the common wiring harness for a short to ground. Repair or replace the malfunctioning part. If there is no common connector: Repair or replace the wiring harness which has a short to ground. Go to Step 7.
		No	Go to the next step.
6	INSPECT WIRING HARNESS BETWEEN AUDIO UNIT AND AUXILIARY JACK/USB PORT FOR OPEN CIRCUIT Verify that the auxiliary jack/USB port and audio unit connectors are disconnected. Inspect for continuity between the following terminals (wiring harness-side): Audio unit terminal 3C—Auxiliary jack/USB port terminal UA Audio unit terminal 3B—Auxiliary jack/USB port terminal UC Audio unit terminal 3D—Auxiliary jack/USB port terminal UB Audio unit terminal 3A—Auxiliary jack/USB port terminal UD Is there continuity?	Yes	Refer to the wiring diagram and verify whether or not there is a common connector between the following terminals: Audio unit terminal 3C—Auxiliary jack/USB port terminal UA Audio unit terminal 3B—Auxiliary jack/USB port terminal UC Audio unit terminal 3D—Auxiliary jack/USB port terminal UB Audio unit terminal 3A—Auxiliary jack/USB port terminal UD If there is a common connector: Determine the malfunctioning part by inspecting the common connector and the terminal for corrosion, damage, or pin disconnection, and the common wiring harness for an open circuit. Repair or replace the malfunctioning part. If there is no common connector: Repair or replace the wiring harness which has an open circuit. Go to the next step.
		No	Go to the next step.
7	VERIFY THAT REPAIRS HAVE BEEN COMPLETED Always reconnect all disconnected connectors. Connect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Clear the audio unit DTCs. (See CLEARING DTC [AUDIO UNIT].) Perform the audio unit DTC inspection. (See DTC INSPECTION [AUDIO UNIT].) Is the same DTC displayed?	Yes	Repeat the inspection from Step 1. If the malfunction recurs, replace the audio unit. (See AUDIO UNIT REMOVAL/INSTALLATION.) Go to the next step.
		No	Go to the next step.
8	VERIFY IF OTHER DTCs DISPLAYED Are any other DTCs displayed?	Yes	Repair or replace the malfunctioning part according to the applicable DTC troubleshooting. (See DTC TABLE [AUDIO UNIT].)
		No	DTC troubleshooting completed.

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