Pinpoint Test H: The Front Axle Makes Noise in 2H Mode Only and Generally Under Heavy Throttle
Four Wheel Drive (4WD) Systems - 1-Speed Torque-On-Demand
Pinpoint Tests
Pinpoint Test H: The Front Axle Makes Noise in 2H Mode Only and Generally Under Heavy Throttle
Refer to Wiring Diagram Set 34, Four-Wheel Drive System for schematic and connector information. Diagrams By Number
Normal Operation
In 4X2 mode, the 4X4 module provides a ground path to the Integrated Wheel End (IWE) solenoid to supply vacuum to each IWE (disengaging the front hubs from the front axle). During certain conditions such as Wide Open Throttle (WOT) maneuvers, manifold vacuum is lower than desired. To maintain uninterrupted IWE function in 4X2, stored engine vacuum is sourced from the vacuum reservoir. A one-way check valve is implemented between the vacuum reservoir and the IWE solenoid to prevent the stored vacuum from escaping into the manifold during low engine vacuum conditions. For noise-free IWE operation under all conditions, the check valve must be operating correctly.
This pinpoint test is intended to diagnose the following:
- Vacuum leaks
- Vacuum check valve
- Vacuum reservoir
- IWE solenoid
- IWE
PINPOINT TEST H: THE FRONT AXLE MAKES NOISE IN 2H MODE ONLY AND GENERALLY UNDER HEAVY THROTTLE
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H1 CHECK FOR GRINDING NOISES AT HIGH SPEEDS
WARNING: When directed to drive the vehicle as part of this test, drive the vehicle on a hard surface in an area without traffic to prevent a crash. Failure to follow these instructions may result in personal injury.
- With the vehicle warm and the Mode Select Switch (MSS) in 4X2 mode, drive the vehicle at sustained WOT for 5 seconds.
- Is there a grinding noise from the axle system during WOT?
Yes
GO to H2.
No
IDENTIFY the customer concern and GO to Symptom Chart - Four-Wheel Drive (4WD). Symptom Chart - Four-Wheel Drive (4WD)
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H2 CHECK THE IWE SOLENOID OUTPUT VACUUM IN 4X2
- NOTE: The engine must be idling during the following steps to supply vacuum to the IWE solenoid.
- Start the engine.
- Disconnect the output vacuum line at the IWE solenoid while having the vacuum supply attached to the solenoid.
- With the engine running and the MSS in 4X2 mode, measure the vacuum at the output port of the IWE solenoid.
- Is the vacuum greater than 254 mm (10 in) Hg?
Yes
GO to H7.
No
GO to H3.
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H3 CHECK THE IWE SOLENOID INPUT VACUUM
- Disconnect the supply vacuum line at the IWE solenoid.
- With the engine still running, measure the supply line vacuum to the IWE solenoid.
- Is the vacuum greater than 254 mm (10 in) Hg?
Yes
INSTALL a new IWE solenoid. TEST the system for normal operation.
No
GO to H4.
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H4 CHECK SOURCE VACUUM TO THE VACUUM RESERVOIR
- Disconnect the source vacuum line from the vacuum reservoir.
- With the engine still running, measure the source vacuum being supplied to the vacuum reservoir.
- Is the vacuum greater than 254 mm (10 in) Hg?
Yes
GO to H5.
No
REPAIR or INSTALL a new source vacuum line. TEST the system for normal operation.
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H5 CHECK THE VACUUM RESERVOIR
- Ignition OFF.
- Disconnect the vacuum line from the vacuum reservoir.
- Connect a hand vacuum pump to the source vacuum port on the vacuum reservoir and apply 508 mm (20 in) Hg of vacuum.
- Does the vacuum maintain or drop less than 25 mm (1 in) Hg per minute?
Yes
GO to H6.
No
INSTALL a new vacuum reservoir. TEST the system for normal operation.
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H6 CHECK THE ONE-WAY VACUUM CHECK VALVE
- NOTE: The check valve is between the IWE solenoid and the vacuum reservoir.
- Connect the vacuum lines to the IWE solenoid.
- Connect a hand vacuum pump to the IWE solenoid vacuum line at the vacuum reservoir and apply 508 mm (20 in) Hg of vacuum.
- Does the vacuum maintain or drop less than 25 mm (1 in) Hg per minute?
Yes
Concern not present at this time. CARRY OUT the Four-Wheel Drive (4WD) System Functional Test. GO to Pinpoint Test I. Pinpoint Test U: Four-Wheel Drive (4WD) System Functional Test Pinpoint Test I: The Vehicle Has No Torque or Inadequate Torque at Rear Wheels in 4X4 Auto Mode
No
REPAIR or INSTALL new vacuum lines or INSTALL a new one-way check valve. TEST the system for normal operation.
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H7 CHECK THE IWE VACUUM SYSTEM
- Ignition OFF.
- Disconnect both vacuum lines from the IWE solenoid.
- Using a hand vacuum pump, apply 508 mm (20 in) Hg of vacuum to the IWE system through the apply vacuum circuit.
- Observe the vacuum reading.
- Does the vacuum maintain or drop less than 25 mm (1 in) Hg per minute?
Yes
CONNECT the vacuum lines to the IWE solenoid. GO to H11.
No
GO to H8.
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H8 CHECK THE RH IWE LEAK RATE
- With the vehicle in NEUTRAL, position it on a hoist. Refer to Vehicle Jacking and Lifting.
- Disconnect the vacuum line from the larger port on the RH IWE.
- Apply 508 mm (20 in) Hg of vacuum to the RH IWE port and observe vacuum reading.
- Does the vacuum maintain or drop less than 25 mm (1 in) Hg per minute?
Yes
GO to H9.
No
INSTALL a new RH IWE. REFER to Integrated Wheel End (IWE) Integrated Wheel End (IWE). GO to H7.
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H9 CHECK THE LH IWE LEAK RATE
- Disconnect the vacuum line from the larger port at the LH IWE.
- Apply 508 mm (20 in) Hg of vacuum to the LH IWE port and observe vacuum reading.
- Does the vacuum maintain or drop less than 25 mm (1 in) Hg per minute?
Yes
GO to H10.
No
INSTALL a new LH IWE. REFER to Integrated Wheel End (IWE) Integrated Wheel End (IWE). GO to H7.
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H10 CHECK THE IWE VACUUM SUPPLY TUBE
- Disconnect both vacuum lines from the IWE solenoid.
- Plug both LH and RH IWE vacuum lines. Apply 508 mm (20 in) Hg of vacuum to the IWE apply vacuum circuit and observe the vacuum reading.
- Does the vacuum maintain or drop less than 25 mm (1 in) Hg per minute?
Yes
GO to H11.
No
INSTALL new vacuum lines as necessary. GO to H7.
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H11 CHECK THE IWE VACUUM SUPPLY AT EACH IWE IN 4X2
- Connect a hand-held vacuum gauge to the LH IWE vacuum supply tube.
- NOTE: The engine must be idling during the following steps to supply the vacuum required for the IWE to engage and disengage.
- Start the engine.
- Switch the MSS to 4X2 mode while observing the vacuum gauge.
- Repeat these steps for the RH IWE.
- Are the vacuum readings greater than 254 mm (10 in) Hg?
Yes
GO to H12.
No
INSTALL new vacuum lines as necessary. GO to H7.
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H12 CHECK THE LH IWE VACUUM LINE FOR AN OBSTRUCTION
- Ignition OFF.
- Disconnect both vacuum lines from the IWE solenoid.
- Disconnect the vacuum line at the LH IWE.
- Connect a hand vacuum pump to the LH IWE vacuum line and attempt to draw a vacuum on the line.
- Did the hand vacuum pump draw a vacuum on the LH IWE vacuum line?
Yes
INSTALL a new vacuum line. TEST the system for normal operation.
No
CONNECT the vacuum line to the LH IWE. GO to H13.
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H13 CHECK THE RH IWE VACUUM LINE FOR AN OBSTRUCTION
- Disconnect the larger vacuum line at the RH IWE.
- Connect a hand vacuum pump to the RH IWE vacuum line and attempt to draw a vacuum on the line.
- Did the hand vacuum pump draw a vacuum on the RH IWE vacuum line?
Yes
INSTALL a new vacuum line. TEST the system for normal operation.
No
CONNECT the vacuum line to the RH IWE. GO to H14.
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H14 CHECK THE LH IWE OPERATION
- Ignition OFF.
- Connect a hand vacuum pump with gauge to the larger port of the LH IWE.
- Observe the LH halfshaft while rotating the LH front tire. Apply between 152 and 203 mm (6 to 8 in) Hg of vacuum and release the vacuum to manually disengage and engage the LH IWE.
- Did the LH IWE disengage between 152 and 203 mm (6 to 8 in) Hg and engage when the vacuum is released?
Yes
GO to H15.
No
INSTALL a new LH IWE. REFER to Integrated Wheel End (IWE) Integrated Wheel End (IWE). TEST the system for normal operation.
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H15 CHECK THE RH IWE OPERATION
- Connect a hand vacuum pump with gauge to the larger port of the RH IWE.
- Observe the RH halfshaft while rotating the RH front tire. Apply between 152 and 203 mm (6 to 8 in) Hg of vacuum and release the vacuum to manually disengage and engage the RH IWE.
- Did the RH IWE disengage between 152 and 203 mm (6 to 8 in) Hg and engage when the vacuum is released?
Yes
GO to Pinpoint Test I. Pinpoint Test I: The Vehicle Has No Torque or Inadequate Torque at Rear Wheels in 4X4 Auto Mode
No
INSTALL a new RH IWE. REFER to Integrated Wheel End (IWE) Integrated Wheel End (IWE). TEST the system for normal operation.
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