Strategy Based Diagnostics
Review the system operations in order to familiarize yourself with the
system functions. Refer to
Differential Carrier Assembly Disassembled Views
and
Differential Carrier Assembly Description
in Rear Drive Axle, and
Transfer Case Description and Operation
in Transfer
Case - NVG 900. All diagnosis on a vehicle should follow a logical
process. Strategy based diagnostics is a uniform approach for repairing all
systems. The diagnostic flow may always be used in order to resolve a system
condition. The diagnostic flow is the place to start when repairs are necessary.
For a detailed explanation, refer to Strategy Based Diagnostics in General
Information.
Visual/Physical Inspection
| • | Inspect for aftermarket devices, which could affect the operation
of the vehicle. |
| • | Inspect the easily accessible or visible system components for
obvious damage or conditions, which could cause the symptom. |
| • | Check for the correct lubricant level and the proper viscosity. |
| • | Verify the exact operating conditions under which the concern
exists. Note factors such as vehicle speed, road conditions, ambient temperature,
and other specifics. |
| • | Compare the driving characteristics or sounds, if applicable,
to a known good vehicle and make sure you are not trying to correct a normal
condition. |
| • | Rear axle activation and operation may be checked by one of the
following: |
On Hoist Function Testing
| - | Raise the vehicle by the frame so that all four wheels hang free. Start
the engine, place in drive and release the brake pedal. All four wheels should
turn. Slowly apply the PARKING brake just enough to stop the rear wheels from
turning. Apply more throttle. If the AWD system is functioning, the rear wheels
will start to turn again. Release the parking brake. |
| - | Raise the vehicle by the frame so that all four wheels hang free. Start
the engine, place in drive and release the brake pedal. All four wheels should
turn. Fully apply the PARKING brake. The rear wheels will stop turning. Apply
throttle while watching the rear wheels. They will move slightly as the driveline
winds-up. This indicates the AWD is functioning. |
| • | Factors that may contribute to an inoperative rear axle include: |
| - | A mini spare or different size tires installed |
| - | A fluid over-temperature condition |
| - | A defective rear axle assembly |
| - | An inoperative transfer case assembly |
Intermittent
Test the vehicle under the same conditions that the customer reported
in order to verify the system is operating properly.
Noise Acceptability
A gear-driven unit will produce a certain amount of noise. Some
noise is acceptable and audible at certain speeds, or under various driving
conditions, such as a newly paved blacktop road. Slight noise is not detrimental
to the operation of the axle and is considered normal.
Symptom List
Refer to a symptom diagnostic procedure from the following list in order
to diagnose the symptom:
