BULLETIN NUMBER:
IB09-N-001H

IMPORTANT SERVICE
INFORMATION FOR:
✓ SERVICE MANAGER
✓ SERVICE ADVISOR
✓ TECHNICIAN
✓ PARTS DEPARTMENT
✓ WARRANTY PERSONNEL

ISSUE DATE:
DECEMBER 2024
GROUP:
ELECTRICAL

ON-VEHICLE ALTERNATOR DIAGNOSTICS AND BATTERY
CHARGING PROCEDURES AND TIPS
AFFECTED VEHICLES
•
•
•

2018MY to current Isuzu FTR
All Isuzu N-Series
Equipped with Gasoline and Diesel Engines
2010MY and Prior GMC/Chevrolet W-Series

This bulletin supersedes bulletin IB09-N-001G. This bulletin is being revised to
update Models and bulletin information. Please discard previous bulletin IB09-N001G.
INFORMATION
CONDITION
Many of the alternator cores returned by dealers have been determined to have No
Trouble Found after testing. All warranty cores returned to the CV Warranty Parts Center
are inspected and tested for quality improvement purposes, including both OEM and
remanufactured cores.
The information set forth in this bulletin is intended to aid technicians in properly testing
the batteries and alternators in the affected Isuzu vehicles. It is important to confirm the
battery is in good condition prior to diagnosis of the alternator and charging system. Never
replace an alternator before testing the battery’s condition. Batteries must be fully charged
for the ECM and/or starter relay to fully engage with the starter. If the battery voltage is
low, the ECM will not engage or may partially engage the starter. Replace the alternator
ONLY if it fails the On Vehicle Testing Procedure.
COMMON SYMPTOMS
•

Battery discharge warning light on.

•

Dim headlights.

•

Noisy operation (such as belts squealing, worn bearings or brushes).

•

No crank/no start (refer to bulletin IB12-N-001 for additional details).

•

Battery voltage is below 11.4 volts – the starter will cycle back and forth into the
flex-plate, which can be inaccurately diagnosed as a starter issue.

BATTERY CHARGING AND TESTING DIAGNOSTIC TIPS
The diagnostic tips set forth below can aid technicians in properly charging and testing a
battery. Replace the battery only when a battery fails the following tests.
NOTE: Absorbed Glass Matt (AGM) batteries require a battery charger designed for
AGM batteries. Using a regular charger can damage AGM batteries and lead
to reduced capacity, shorter lifespan, and potential failure of the AGM battery over
time.
Caution: Overcharging an AGM battery can lead to gas venting, which poses safety
risks, including the potential for explosion if the gas ignites.
COMMON CAUSES
The following are some common causes that may contribute to a weak or dead battery.
•

The vehicle headlights and accessories are left on for an extended period of time.

•

A fault or flaw in the vehicle charging system.

•

The electrical load of the vehicle exceeds the alternator capacity (such as
Bodybuilder add-on power equipment).

•

Extended slow speed driving with many accessories turned on.

•

Loose or poor battery cable to post connection or corrosion.

•

High parasitic drain (greater than 50mA).

•

Loose belt.

•

A fault or flaw in the vehicle’s electrical system (such as shorted or pinched wires).

•

There may be a faulty starter or cranking circuit.

•

Slow, extended or no engine cranking.

•

Vehicle stored for a long period of time (See the Service Policy and Procedure
Manual (SP&P), Article 2.15 and 2.16).

Caution: Batteries produce explosive gases, contain corrosive acid and supply
levels of electrical current high enough to cause skin burns. Therefore, to reduce
the risk of personal injury when working near a battery, always shield your eyes
and avoid leaning over the battery whenever possible. Do not expose the battery
to open flames or sparks. Avoid spilling battery fluid (electrolyte). Flush any
contacted area with water immediately and get medical help if eyes are affected.
BATTERY CHARGING TIPS
If the vehicle is equipped with more than one battery, disconnect the cables to
inspect/charge/test each battery separately in a well-ventilated area.
•

Most batteries are maintenance-free and have a Hydrometer built in for a visual
check.

o Green dot = 65% or above state-of-charge; sufficient for load test.
o Dark = below 65% state-of-charge; charging required.
o Clear or Light Yellow = Low fluid level. This may have been caused by
excessive or prolonged charging, a broken/damaged case, a seal leak, the
battery tipping over or normal battery wear-out. Replace the battery. Do not
attempt to charge, test or jump start the battery.
•

Charging rates between 3 and 50 amps are satisfactory as long as there is no
spewing of fluid and the battery does not feel excessively hot over 51°C (125°F).
If any of these conditions occur while charging, it will be necessary to reduce
amperes or temporarily stop to cool down.

An automatic charger will monitor the charger output based on the battery status to protect
the battery from overcharging/overheating, but the battery still should be checked every
30 minutes to ensure it is not overcharging and/or overheating.
•

The time required for a charge will vary. This is usually measured in hours. For
instance, charging at a rate of 25 amperes for two hours would provide the
battery with a 50 ampere-hour charge.
o Battery Size — A completely discharged large, heavy-duty battery would
require charging more than twice as long as a small passenger car
battery.
o Temperature — A longer time will be needed to charge any battery at
-17°C (0°F) than at 21°C (70°F). A warmer battery will accept more
charging current.
o State-of-Charge — A completely discharged battery will require charging
more than twice as much as a half-charged battery.
o Charger Capacity — A charger that can supply only 5 amps will take much
longer to charge a battery than will a 30-amp charger.

BATTERY TESTING
If the vehicle is equipped with more than one battery, disconnect the cables to
inspect/charge/test each battery separately in a well-ventilated area. Be sure that the
battery is properly charged, and the Hydrometer has a green dot visible before testing.
Test the battery using a Vehicle Charging/Starting System Tester, commonly known as
VAT40 or Snap-On MT1552, or equivalent.
1. Connect the positive lead of the tester to the positive (+) post of the battery, and
the negative lead of the tester to the negative post of the battery.
2. Monitor the battery voltage with the key OFF. Battery voltage should range
between 12V and 13V. If the voltage is within this range, the battery circuit is good.
Voltages below this range indicate that the battery needs to be charged before
testing. Voltages above this range indicate a failed battery that needs to be
replaced.
3. Connect the round current-probe cable of the tester onto either of the power leads
to measure the current draw.
4. Determine the Cold Cranking Amps (CCA) rating of the battery.

5. Apply a load of 1⁄2 the CCA rating for 15 seconds and take a voltage reading at
the end, before releasing the load. Turn off load and wait for 15 seconds to allow
the battery to recover before repeating test, if necessary.

6. Depending on the battery temperature, if the voltage does not drop below the
minimum voltage as shown in the reference table below, then the battery is good
and should be returned to service. If the voltage does drop below the referenced
voltage, charge the battery until fully charged and then retest the battery.
Temperature
21°C (70°F)
10°C (50°F)
-1°C (30°F)
-10°C (14°F)
-18°C (0°F)

Minimum
Voltage
9.6
9.4
9.1
8.8
8.5

TESTING FOR PARASITIC DRAIN
A parasitic drain is when an electrical device is using battery power when the vehicle is
off, and the key is in the “OFF” position and removed. Therefore, when testing, make sure
the key is OFF and removed for at least 5 minutes and all other electrical devices, like the
dome light, are OFF.
1. Turn the key OFF and remove. Inspect the vehicle for any other electrical devices
that may still be drawing current and turn them off.
2. Install a 10A or 20A capable multimeter between the negative battery cable and
the negative battery terminal.
3. Monitor the amperage for a few minutes after the amperage reading stabilizes
(when the ammeter is connected the vehicle control modules may wake up). If the
amperage is under 50mA the current drain is normal.
NOTE: Current drain over 50mA is caused by a continuous electrical load. Locate the
system generating the excessive load and repair as necessary. Be sure to isolate the
body application for potential causes.

AMMETER

+
-

+

ON-VEHICLE ALTERNATOR TESTING PROCEDURE
Be sure that the belts are not slipping, and the battery is fully charged for a valid test. Also
all other electrical problems must be corrected prior to testing. Refer to the applicable
Workshop Manual (WSM) for specific electrical wiring schematics.
Test the alternator using a Charging/Starting System Tester, commonly known as VAT40
or Snap-on MT1552, or equivalent.
1. Connect the positive lead of the tester to the positive post of the vehicle’s battery,
and the negative lead of the tester to the negative post of the vehicle’s battery.
2. Place the round current-probe cable of the tester onto the B-terminal of the
alternator.
•

Test #1 — Under no electrical load and cold condition with all accessories
off (A/C, headlights, radio, wipers), the regulating voltage should be
between 13V and 15V with the engine running at 2,000 rpm.

•

Test #2 — Begin the test under no electrical load and in a cold condition,
with all accessories still off and the engine running at 2,000 rpm. Apply an
electrical load by turning the tester’s Load Control knob clockwise until a
reading of 50% of the battery’s CCA rating is displayed.
o For an alternator rated 80 Amp, the output current should be more
than 50A.
o For an alternator rated 110 Amp, the output current should be more
than 70A.
o For an alternator rated 140 Amp, the output current should be more
than 88A.
o For an alternator rated at 145 Amps, the output current should be
more than 105A.