Mazda MX-5 Miata / Grand Touring. Manual — part 42

9. Turn the following electrical loads on and verify that the current reading increases more than the

minimum value indicated below.



If it is not as specified, go to the PCM AND GENERATOR SHEARING INSPECTION.



Headlights (high-beam)



Blower motor (HI)



Rear window defroster



Brake light

Generator generated current minimum value

70% of the nominal output current (nominal output current: 100 A)

[ambient temp. 20°C {68°F}, voltage 13.0-15.0 V, both engine and generator are hot]

PCM AND GENERATOR SHEARING INSPECTION

1. Connect the M-MDS or equivalent to the DLC-2.

will not be verified although the generator is normal. In this case,
increase the electrical load (by turning on the headlight and leave it
for a while, then discharge the battery or by similar methods) and
recheck.



When the generator itself or the ambient temperature are too high,
the specified current cannot be verified. In this case, cool down the
generator and recheck.

2008 Mazda MX-5 Miata Grand Touring

2008 ELECTRICAL Charging System - MX-5 Miata

Fig. 9: Locating DLC-2 Connector
Courtesy of MAZDA MOTORS CORP.

2. Inspect as follows:

PCM AND GENERATOR SHEARING INSPECTION TABLE

Step

Inspection

Action

1 Measure the generator terminal B voltage when the electrical loads

(1)

are

on and off.

15 V
or
more

Go to Step 2.

13-15
V

Normal

(2)

13 V
or less

Go to Step 3.

2

Monitor the ALTT V PID using the M-MDS or equivalent, or measure
the voltage of PCM terminal 2AJ using a tester. Is the voltage between 13
and 15 V?

Yes

Go to Step 4.

No

PCM input error.

3

Monitor the ALTT V PID using the M-MDS or equivalent, or measure
the voltage of PCM terminal 2AJ using a tester. Is the voltage between 13
and 15 V?

Yes

Go to Step 5.

No

PCM input error.

Monitor the ALTF PID using the M-MDS or equivalent, or calculate the
duty value of the PCM terminal 2AI using an oscilloscope. Is the duty

Yes

PCM input error.

2008 Mazda MX-5 Miata Grand Touring

2008 ELECTRICAL Charging System - MX-5 Miata

GENERATOR INNER PARTS

Rotor

1. Measure the resistance between the slip rings using a tester.



If not within the specification, replace the rotor.

Generator rotor resistance (between slip rings) [20°C {68°F}]

2.0-2.3 ohm

4

value 100%?

No

PCM, generator,
or both are not
normal.

5

Monitor the ALTF PID using the M-MDS or equivalent, or calculate the
duty value of the PCM terminal 2AI using an oscilloscope. Is the duty

value 0%?

Yes

PCM input error.

No

PCM, generator,
or both are not
normal.

(1)

Headlights, blower motor, rear window defroster, and brake light.

(2)

If the generator field coil duty value does not change when electrical loads (such as headlights,
blower motor, rear window defroster, brake light) are on or off, inspection with discharged battery is
needed.

2008 Mazda MX-5 Miata Grand Touring

2008 ELECTRICAL Charging System - MX-5 Miata

Fig. 10: Measuring Resistance Between Slip Rings Using Tester
Courtesy of MAZDA MOTORS CORP.

2. Verify that there is no continuity between the slip ring and core using a tester.



If there is continuity, replace the rotor.

2008 Mazda MX-5 Miata Grand Touring

2008 ELECTRICAL Charging System - MX-5 Miata