Step 9, restore truck to operating
condition and contact your
supervisor.

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IK0800403 ­ Alternator Troubleshooting and Diagnostics

Step Action

Leece Neville Symptom Verification

11

• Alternator voltage is intermittently high (above the
normal running range of 13.8-14.8V).
• Voltage as seen on the volt gauge spikes above
15V temporarily, and then drops to normal range.
• Voltage gauge fluctuates abnormally.
Is the Vehicle experiencing any of the issues above?

Page 4 of 8

Decision
Yes: Replace Alternator and Retest(See Appendix C
for replacement guidelines)

No: Go to Step 12, if Step 9 was unable to be
performed.

No : If cable drop has already been performed.
Restore truck to operating condition, and contact your
supervisor

Step Action

Decision

Positive Cable Circuit Test if Midtronics Cable Drop Test Leads (DMM Test Leads)
are not available
(Illustration in Appendix A)
1. Connect Ammeter to positive alternator Cable
2. Make sure Ammeter is atleast 6 inches away from alternator to eliminate the
possibility of faulty readings.

Yes: Correct voltage drop, and retest before proceeding

3. Connect Voltemeter's negative lead to the positive terminal of the alternator
4. Connect the voltmeter's positive lead to the positive terminal of the battery.
12

5. Start engine and set engine 1500 RPM's
6. Turn on vehicle loads until 75% of alternators rated output is acheieved on
ammeter display
7. If necessary, use a carbon pile tester to apply load on alternator
8. Record Measured voltage to checklist
9. Turn off engine
No: Go to Step 13
Note : Record measured voltage drops into the Alternator Diagnostic
Worksheet

Was the reading greater than .25 Volts (+/­ 0.10V)?
Step
13

Action

Decision

Yes: Correct voltage drop,and re­
Negative Cable Circuit Test if Midtronics Cable Drop Test Leads (DMM Test Leads) test before proceeding
are not available
No: Restore truck to operating
condition and contact supervisor
(Illustration Shown in Appendix B)
1. Connect Ammeter to positive alternator Cable
2. Make sure Ammeter is atleast 6 inches away from alternator to eliminate the
possibility of faulty readings.
3. Connect Voltemeter's negative lead to the negative terminal of the Battery
4. Connect the voltmeter's positive lead to the negative output terminal on the
alternator.
5. Start engine and set engine 1500 RPM's
6. Turn on vehicle loads until 75% of alternators rated output is acheieved on
ammeter display
7. If necessary, use a carbon pile tester to apply load on alternator
8. Record Measured voltage to checklist
9. Turn off engine

Note : Record measured voltage drops into the Alternator Diagnostic
Worksheet
Note : Clean and tighten connections, or replace wiring as needed

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IK0800403 ­ Alternator Troubleshooting and Diagnostics

Page 5 of 8

Note : Refer to the table, "Charging System Decision" in the Midtronics
Instruction Manual. Follow instructions for further inspections and re-tests

Was the reading greater than .25V (+/- 0.10V) Volts?

WARRANTY INFORMATION
When troubleshooting a replacing an alternator, technicians must utilize the Midtronics EXP Tester, and submit a Alternator Diagnostic
Worksheet. Critical diagnostic testing values are to be recorded on the worksheet, and submitted with the claims on iClaim.
Exception: Worksheet is not required for over-the-counter parts warranty when no vehicle is present to perform diagnostics.
NOTE : A Midtronics Alternator 9 Digit Charge Code is now required on all alternator replacements. Only exception being 55 Over the Counter Parts
Warranty replacement.
Warranty Return Information
Due to the high rate of damaged alternators, any and all alternators sent back via warranty/service contract/service part must be undamaged and testable.
Unwarrantable Damage includes :
Stripped pulley/terminal threads
Missing/damaged terminals
Foreign object damage
Missing parts that render unit untestable
Cracked Housing
Alternators returned in disassembled condition
Warranty Claim Coding:

Group: 08000 - Generating System
Noun:

018 - Alternator Assy

Standard Repair Times:

Description

SRT Link or Code

Hours

Alternator Diagnostics

Select model

0.5

Positive Cable Test

Select model

0.1

Negative Cable Test

Select model

0.1

Replace Alternator

Select model

Select model

APPENDIX
Appendix A :
Perform the following manual voltage drop tests:

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IK0800403 ­ Alternator Troubleshooting and Diagnostics

Page 6 of 8

A. Positive Cable Test
1. Connect ammeter to positive alternator cable.
2. Make sure ammeter is at least 6 inches (15 cm) away from alternator, to eliminate possibility of faulty readings.
3. Connect voltmeter’s negative lead to positive terminal of alternator.
4. Connect voltmeter's positive lead to positive terminal on battery.
5. Start engine and set engine 1500 RPMs.
6. Turn on vehicle loads until 75% of alternator’s rated output is achieved on ammeter display.
7. If necessary, use a carbon pile tester to apply load on alternator.
8. Record measured voltage to checklist.
9. Turn off engine.
Appendix B :

B. Negative Cable Test
1. Connect ammeter to positive alternator cable.
2. Verify the ammeter is at least 6 inches (15 cm) away from alternator, to eliminate possibility of faulty readings.
3. Connect voltmeter’s negative lead to negative terminal of battery.
4. Connect voltmeter's positive lead to negative output terminal on alternator.
5. Start engine and set engine 1500 RPMs.
6. Turn on vehicle loads until 75% of alternator’s rated output is achieved on ammeter display.
7. If necessary, use a carbon pile tester to apply load on alternator.
8. Record measured voltage to checklist.
9. Turn off engine.
Appendix C :
Action

Corrections and Warranty Determination
Part label must be intact. If label is missing or destroyed, a justifiable reason must be
presented and accepted by a representative before a claim process is initiated. A
missing or intentionally destroyed label may void the warranty.

1. Record alternator date code
If date code is newer than vehicle manufacture or in-service date, this is a replacement part. The
date code must coincide with the date of invoice when the part was purchased, or be validated by
an “install date”.
2. Inspect for excessive dirt, grease, or oil

Excessive dirt, grease, or oil soaked/saturated condition: Oil and grease on surface and/or interior
of alternator will prevent unit from cooling properly, causing premature failure. This may also create
a low voltage condition on the vehicle.

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IK0800403 ­ Alternator Troubleshooting and Diagnostics

Page 7 of 8

Check and correct any sources of excessive oil, grease, and dirt. Check for missing shields,
leaking hoses, or fraying belts.

3. Inspect for rust and corrosion.

Alternators can become rusted or corroded such that they cannot function, or function
intermittently. Examples are positive side rectifiers shorted to case by a “corrosive bridge”, the rotor
rusted and seized to the stator, or electrical connections open due to corrosion.

4. Inspect for damaged shaft, mounting bosses, housing

Bent, broken, cracked or elongated mounting holes, impact marks or cracked
housings render all products unacceptable for warranty.

5. Inspect for signs of arcing or shorts to housing or connection
points.

Signs of arcing or direct shorts to housing or connection points, including hardware dropped or
loose inside of alternator housing, improperly connected or modified electrical connectors, or
cut/severed wires will void warranty.

6. Inspect mounting brackets

Make sure charging system components are securely mounted to their applicable brackets.
Brackets, in turn, must be bolted securely to the engine. Poorly mounted charging system
components lead to vibration damage and diminished drive belt performance.

Appendix D :

Appendix E :

Appendix F :
Leece Neville Terminal ID Chart :

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IK0800403 ­ Alternator Troubleshooting and Diagnostics

Page 8 of 8

Delco Remy Terminal ID Chart :
Terminal

Function

Battery Positive (B+) and
Ground Terminals : all case
grounded alternators

Alternator output terminals

Battery Positive (B+) and
Battery Negative (B-) : all
case insulated alternators

Alternator output terminals

Relay (R) Terminal or Phase
(P) Terminal

Alternating speed signal at 1/2 system voltage
(Half wave rectified. A terminal is provided to
monitor the voltage of one phase. The maximum
current loading is 4 amps, and may be used for
tachometers, hour meters etc...

Indicator (I) Terminal

Constant current source or sink to reduce turn-on
speed or indicate fault (1 amp max). This terminal
carries full system voltage

Lamp (L) Terminal

Constant 1 amp current sink only to indicate
charging system condition. The L terminal will
function as a fault indicator by pulling the applied
voltage low, and hence terminal L is capable of
sinking a current of up to 1 Amp indefinitely when
the alternator is not working

Sense (S) Terminal

Connection point for remote voltage
sensing. Battery voltage may be sensed using an
external sense. In the event the sense wire
becomes disconnected, or is not in use, the
battery voltage sense circuit will automatically
revert to internal sensing on most models

Field (FM) Terminal

Available on only certain products. The FM
terminal is used to monitor the pulse width
modulated (PWM)field voltage. With the alternator
field referenced to ground, the FM terminal is
connected to the high side of the field using a
10,000 ohm resistor. When the field switch is
turned on, essentially battery voltage appears at
the FM terminal, nad thus the average voltage a
Terminal FM is directly proportional to field
strength. When the ECU recognizes a full filed
condtion, it can activate fast idle to maintain
required loads

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