Mazda 6. Manual - part 348

T–146–2

ON-BOARD DIAGNOSTIC [DISCHARGE HEADLIGHT] 

RHID

End Of Sie

DTC B2386

A6E818867000W05

Diagnostic procedure

End Of Sie

DTC B2387

A6E818867000W06

Diagnostic procedure

PID Name

(Definition)

Unit/

Condition

Condition/Specification

 Discharge headlight 

control unit (RH) 

terminal

CCNT
(Number of continuous codes)

—

• DTC is detected: 1—255

• DTC is not detected: 0

—

ONDEMDTC
(Number of on-demand codes)

—

• DTC is detected: 1—255

• DTC is not detected: 0

—

L_VOLT_R
(Discharge headlight control unit (RH) input 
voltage)

VOLTAGE

Headlight switch at ON: 

B+

D

GDL_P_R
(Output power to discharge headlight bulb (RH))

WATT

Headlight switch at ON: 

35—65 W

—

GDL_V_R
(Output voltage to discharge headlight bulb 
(RH))

VOLTAGE

Headlight switch at ON: 

68—112 V

—

DTC B2386

Discharge headlight illumination malfunction

DETECTION 

CONDITION

Warning
• Incorrect servicing of the discharge headlight control unit could result in electrical shock. 

Before servicing the discharge headlight control unit, always refer to “Discharge headlight 
service warnings”. (See 

T–25 DISCHARGE HEADLIGHT SERVICE WARNINGS

)

• Discharge headlight does not illuminate though preparation has been completed.

POSSIBLE 

CAUSE

• Discharge headlight bulb malfunction

• Ignitor in front combination light is malfunctioning.

STEP

INSPECTION

ACTION

1

• Are DTCs B2388 and/or B2389 indicated?

Yes

Replace discharge headlight bulb.
(See 

T–28 HEADLIGHT BULB REMOVAL/

INSTALLATION

)

No

Ignitor in front combination light may be malfunctioning. 
Replace front combination light.
(See 

T–26 FRONT COMBINATION LIGHT REMOVAL/

INSTALLATION

)

DTC B2387

Ignitor circuit malfunction

DETECTION 

CONDITION

Warning
• Incorrect servicing of the discharge headlight control unit could result in electrical shock. 

Before servicing the discharge headlight control unit, always refer to “Discharge headlight 
service warnings”. (See 

T–25 DISCHARGE HEADLIGHT SERVICE WARNINGS

)

• Ignitor in front combination light is malfunctioning or poorly connected.

POSSIBLE 

CAUSE

• Ignitor in front combination light is malfunctioning.

• Ignitor in front combination light is poorly connected.

STEP

INSPECTION

ACTION

1

INSPECT CONNECTOR CONNECTION

• Check fit of discharge headlight control unit and 

headlight connectors on both sides (discharge 
headlight control unit (LH) and (RH)).

• Are installation condition and fit okay?

Yes

Ignitor in front combination light may be malfunctioning. 
Replace front combination light.
(See 

T–26 FRONT COMBINATION LIGHT REMOVAL/

INSTALLATION

)

No

After correcting fit, clear DTC and check DTC again.

• If DTC is displayed again, replace front combination 

light.
(See 

T–26 FRONT COMBINATION LIGHT 

REMOVAL/INSTALLATION

)

ON-BOARD DIAGNOSTIC [DISCHARGE HEADLIGHT] 

T–146–3

T

End Of Sie

DTC B2388

A6E818867000W07

Diagnostic procedure

End Of Sie

DTC B2389

A6E818867000W08

Diagnostic procedure

DTC B2388

Discharge headlight operating voltage out of range.

DETECTION 

CONDITION

Warning
• Incorrect servicing of the discharge headlight control unit could result in electrical shock. 

Before servicing the discharge headlight control unit, always refer to “Discharge headlight 
service warnings”. (See 

T–25 DISCHARGE HEADLIGHT SERVICE WARNINGS

)

• Discharge headlight operating voltage is outside specification (68V—112V) when inspected 3 minutes 

after illumination.

POSSIBLE 

CAUSE

• Discharge headlight bulb malfunction

• Discharge headlight bulb life

STEP

INSPECTION

ACTION

1

INSPECT DISCHARGE HEADLIGHT BULB

• Does discharge headlight illuminate normally?

Yes

After correcting fit, clear DTC and check DTC again after 
more then 3 minutes low beam on.

• If DTC is displayed again, replace discharge 

headlight bulb. 
(See 

T–28 HEADLIGHT BULB REMOVAL/

INSTALLATION

)

No

Replace discharge headlight bulb. 
(See 

T–28 HEADLIGHT BULB REMOVAL/

INSTALLATION

)

DTC B2389

Discharge headlight illumination malfunction

DETECTION 

CONDITION

Warning
• Incorrect servicing of the discharge headlight control unit could result in electrical shock. 

Before servicing the discharge headlight control unit, always refer to “Discharge headlight 
service warnings”. (See 

T–25 DISCHARGE HEADLIGHT SERVICE WARNINGS

)

• Automatic reillumination (discharge headlight reilluminates automatically when illumination is 

interrupted during normal illumination) occurs twice within 1 minute.

POSSIBLE 

CAUSE

• Discharge headlight bulb malfunction

• Discharge headlight bulb life

STEP

INSPECTION

ACTION

1

INSPECT DISCHARGE HEADLIGHT BULB

• Does discharge headlight illuminate normally?

Yes

After correcting fit, clear DTC and check DTC again.

• If DTC is displayed again, replace discharge 

headlight bulb. 
(See 

T–28 HEADLIGHT BULB REMOVAL/

INSTALLATION

)

No

Replace discharge headlight bulb. 
(See 

T–28 HEADLIGHT BULB REMOVAL/

INSTALLATION

)

T–146–4

ON-BOARD DIAGNOSTIC [DISCHARGE HEADLIGHT] 

End Of Sie

DTC B2391

A6E818867000W09

Diagnostic procedure

DTC B2391

Discharge headlight input resistance too high

DETECTION 

CONDITION

Warning
• Incorrect servicing of the discharge headlight control unit could result in electrical shock. 

Before servicing the discharge headlight control unit, always refer to “Discharge headlight 
service warnings”. (See 

T–25 DISCHARGE HEADLIGHT SERVICE WARNINGS

)

• Discharge headlight does not illuminate because of voltage drops caused by high impedance on input 

path for supply voltage.

POSSIBLE 

CAUSE

• Resistance in related wiring harness too high

• Resistance in front combination light internal harness too high.

STEP

INSPECTION

ACTION

1

INSPECT CONNECTOR CONNECTION

• Check fit of discharge headlight control unit and 

headlight connectors.

• Are installation condition and fit okay?

Yes

Go to next step.

No

After correcting fit, clear DTC and check DTC again.

• If DTC is displayed again, go to next step.

2

INSPECT WIRING HARNESS

• Disconnect headlight connector (12-pin).

• Measure resistance of headlight connector 

terminal 1C to battery negative terminal.

• Measure resistance of headlight connector 

terminal 1B to battery positive terminal.

• Is sum of resistances more than 1.5 ohms?

Yes

Repair related wiring harness.

No

Front combination light internal harness may have too 
high impedance. Replace front combination light.
(See 

T–26 FRONT COMBINATION LIGHT REMOVAL/

INSTALLATION

)

HEADLIGHT (LH)

HARNESS SIDE CONNECTOR

1K

1I

1G 1E

1H 1F

1L

1J

1C 1A

1D 1B

HEADLIGHT (RH)

HARNESS SIDE CONNECTOR

1K

1I

1G 1E

1H 1F

1L

1J

1C 1A

1D 1B

ON-BOARD DIAGNOSTIC [DISCHARGE HEADLIGHT] 

T–146–5

T

End Of Sie

DTC B2392

A6E818867000W10

Diagnostic procedure

End Of Sie

DTC B2393

A6E818867000W11

Diagnostic procedure

End Of Sie

DTC B2392

Discharge headlight Input voltage high

DETECTION 

CONDITION

Warning
• Incorrect servicing of the discharge headlight control unit could result in electrical shock. 

Before servicing the discharge headlight control unit, always refer to “Discharge headlight 
service warnings”. (See 

T–25 DISCHARGE HEADLIGHT SERVICE WARNINGS

)

• Voltage detected at discharge headlight control unit terminals D is more than 19 V.

POSSIBLE 

CAUSE

• Short to power circuit between generator and PCM

• Generator malfunction

• Battery malfunction

• Discharge headlight control unit malfunction

STEP

INSPECTION

ACTION

1

INSPECT BATTERY VOLTAGE

• Measure battery voltage.

• Is voltage less than 19 V?

Yes

Go to next step.

No

Inspect charging system.

2

INSPECT DISCHARGE HEADLIGHT CONTROL 
UNIT

• Clear DTC.

• Read DTCs using SST (WDS or equivalent).

• Is DTC B2392 displayed again?

Yes

Replace discharge headlight control unit.
(See 

T–30 DISCHARGE HEADLIGHT CONTROL UNIT 

REMOVAL/INSTALLATION

 )

No

Troubleshooting completed.

DTC B2393

Discharge headlight control unit output circuit malfunction

DETECTION 

CONDITION

Warning
• Incorrect servicing of the discharge headlight control unit could result in electrical shock. 

Before servicing the discharge headlight control unit, always refer to “Discharge headlight 
service warnings”. (See 

T–25 DISCHARGE HEADLIGHT SERVICE WARNINGS

)

• Abnormal output from discharge headlight control unit to ignitor.

POSSIBLE 

CAUSE

• Open circuit, short to ground or short to power circuit in front combination light internal harness

STEP

INSPECTION

ACTION

1

INSPECT CONNECTOR CONNECTION

• Check fit of discharge headlight control unit and 

headlight connectors on both sides (discharge 
headlight control unit (LH) and (RH)).

• Are installation condition and fit okay?

Yes

Go to next step.

No

After correcting fit, clear DTC and check DTC again.

• If DTC is displayed again, go to next step.

2

INSPECT DISCHARGE HEADLIGHT CONTROL 
UNIT

• Replace discharge headlight control unit.

(See 

T–30 DISCHARGE HEADLIGHT 

CONTROL UNIT REMOVAL/INSTALLATION

)

• Does discharge headlight illuminate normally?

Yes

Troubleshooting completed.

No

Ignitor in front combination light may be malfunctioning. 
Replace front combination light.
(See 

T–26 FRONT COMBINATION LIGHT REMOVAL/

INSTALLATION

)