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2008 - MX-5 - Body and Accessories

NO.3 NOISE FROM RADIO (FM ONLY) [AUDIO]



3

Noise from radio (FM only) / Possible DTC: 09:Er22

POSSIBLE CAUSE

  • Antenna rod is not installed (standard part)

  • Jamming from aftermarket electronic equipment (two-way radio, navigation system, mobile phone, etc.)

  • Noise from electrical system on vehicle (e.g. fuel pump)

  • Battery malfunction

  • Charging system malfunction

  • Audio unit malfunction

  • Poor connection of antenna feeder plug

  • Antenna feeder malfunction

  • Open or short circuit in wiring harness between audio unit and manual antenna (antenna amplifier power supply system)

  • Electronic jamming from outside, or inferior condition of broadcasting station radio wave

  • Antenna installation loosened

NOTE:

  • FM broadcasts are known for good sound quality and resistance to noise, but FM broadcasts do carry characteristic noise. Though the audio unit is designed to reduce noise, there are times when noise occurs due to reception conditions.


Diagnostic procedure

STEP

INSPECTION

ACTION

1

  • Tune to a local broadcasting station and check the reception condition.

  • Is the reception normal?

Yes

Tune to the correct frequency for the broadcasting station.

If not preset, preset it.

No

Go to the next step.

2

  • Inspect the antenna rod condition.

  • Is the antenna rod installed?

Yes

Go to the next step.

No

Advise the customer to install the antenna rod when the radio is used.

(It the antenna rod is not a standard part, replace it.)

3

  • Is aftermarket electronic equipment (two-way radio, navigation system, mobile phone, etc.) installed?

Yes

Go to the next step.

No

Go to Step 5.

4

  • Remove aftermarket electronic equipment.

  • Turn the audio unit on and check the reception condition.

  • Does the reception improve?

Yes

The system is normal. (Explain to the customer that the aftermarket electronic equipment is the cause of the noise)

No

Go to the next step.

5

  • Measure the battery voltage.

  • Is the battery voltage normal?

    Standard
  • With ignition switch ON: 11.5 V or more

  • At idling: 12.5 V or more

NOTE:

  • Verify that the battery cables are connected to the terminals securely.

Yes

Go to the next step.

No

Charge the battery. Inspect the charging system, and repair or replace if necessary.

6

  • Does the noise occur only when the vehicle’s electrical system (e.g. fuel pump) operates?

NOTE:

  • Identify the suspect electrical component by disconnecting fuses, turning switches on & off, or disconnecting and connecting connectors.

  • It is easier to use the simulation function on the M-MDS.

Yes

Go to the next step.

No

Go to Step 8.

7

  • Verify the condition of the power supply and ground of the electric components, and the noise prevention capacitor.

  • Is the noise present after inspection?

NOTE:

  • Inspect the following:

    • Power supply to electrical component for voltage drop (compare with battery voltage)

    • Resistance between ground of electrical component and body. (Should be close to 0 ohm)

    • Installation condition of noise prevention capacitor for fuel pump.

Yes

Go to the next step.

No

Troubleshooting completed.

8

  • Inspect the antenna feeder plug connection condition.

  • Is the connection normal?

Yes

Go to the next step.

No

Insert the antenna feeder plug securely.

9

  • Turn the ignition switch to the LOCK position.

  • Measure the continuity between the antenna feeder axis and ground.

  • Is there any continuity?

Yes

Replace the antenna feeder.

(See ANTENNA FEEDER LOCATION.)

No

Go to the next step.

10

  • Turn the ignition switch to the LOCK position.

  • Inspect the continuity between audio unit terminal H (24-pin) and manual antenna terminal A.

  • Is there any continuity?

Yes

Go to the next step.

No

Repair or replace the wiring harness between the audio unit and the manual antenna (antenna amplifier power supply system), then verify the reception condition.

If the reception has improved, troubleshooting is completed.

If the reception has not improved, go to the next step.

11

  • Measure the voltage at audio unit terminal H (24-pin) to verify the antenna amplifier power supply.

  • Is the voltage B+?

NOTE:

  • 12 V is supplied from the audio unit to the antenna amplifier. (In radio mode)

  • Even if the power supply voltage is not supplied, FM reception is possible, however, noise interference occurs more easily.

Yes

Go to the next step.

No

Replace the audio unit.

(See CENTER PANEL UNIT REMOVAL/INSTALLATION.)

(See CENTER PANEL UNIT DISASSEMBLY/ASSEMBLY.)

(See AUDIO UNIT DISASSEMBLY/ASSEMBLY.)

12

  • Compare the reception with another audio unit on the same model (model/unit) under the same problem conditions.

  • Is the reception equivalent to the customer’s unit?

Yes

The system is normal (It is caused by electronic jamming from outside, or inferior broadcasting station signal condition).

No

Go to the next step.

13

  • Retighten the ground for the antenna installation part and antenna amplifier. Retighten the antenna rod.

  • Is the noise present, after retightening?

NOTE:

  • When the antenna is not grounded properly, FM noise is likely to be noticed.

Yes

Replace the audio unit.

(See CENTER PANEL UNIT REMOVAL/INSTALLATION.)

(See CENTER PANEL UNIT DISASSEMBLY/ASSEMBLY.)

(See AUDIO UNIT DISASSEMBLY/ASSEMBLY.)

No

Troubleshooting completed.




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