Pinpoint Test F : Grinding / Clicking / Ratcheting Noise From Front Axle In 2H Mode Under Acceleration Or Heavy Loads

Normal Operation and Fault Conditions 

Locator views for the vacuum lines and vacuum reservoir are located in Description and Operation. REFER to: Four-Wheel Drive Systems - System Operation and Component Description .

In 2H mode, the TCCM provides a ground path to the IWE solenoid to supply vacuum to each IWE (disengaging the front hubs from the front axle). During certain conditions such as WOT maneuvers, manifold vacuum is lower than desired. To maintain uninterrupted IWE function in 2H, 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.

When following this diagnostic procedure please note the following since these system interactions may influence the results: 

• When shifting to 2H mode in order for the IWE to completely disengage the vehicle steering wheel must be less than 90 degrees and 5 seconds have elapsed since the shift to 2H has been initiated.

The TCCM has two startup strategies that affect IWE operation after initial key cycle: 

• When ambient temperature is below 32 F (0 deg. C), the IWE engage after initial key cycle and a driven gear is selected. The hubs stay engaged regardless of 4WD mode until 2 miles (3km) have been traveled above 6 mph (10 km/h). Once the set distance has been achieved, the IWE disengage (if the vehicle is in 2WD (2H)). Distance traveled resets only if the temperature is below calibrated threshold and another key cycle occurs or if customer shifts to Park (P) and back to a driven gear within the same key cycle. The TCCM uses this strategy to warm up the front axle in cold temperatures to improve driveline synchronization.

• When ambient temperature is above 32 F (0 deg. C), the IWE engage after the initial key cycle and a driven gear is selected. The hubs stay engaged regardless of 4WD mode until 0.5 miles (0.8km) have been traveled above 6 mph (10 km/h). Engagement only occurs once per key cycle and is not reset when shifting between Park (P) and Drive (D). The TCCM uses this strategy to delay vacuum use until vacuum-intensive engine startup has completed and sufficient vacuum is available to fully disengage the IWE.

Possible Sources 

• Vacuum check valve
• Vacuum reservoir
• Vacuum supply line
• IWE solenoid
• Vacuum lines between IWE solenoid and IWE
• IWE
• IWE Cutch ring

• Ignition ON.

• Enter the following diagnostic mode on the scan tool: TCCM KOEO Self -Test.

Are any DTC present? 

• Ignition OFF.

• Disconnect the vacuum line leading to the IWE solenoid from the one-way vacuum check valve.

• Connect a hand vacuum pump and apply 508 mm (20 in) Hg of vacuum to the check valve.

Does the vacuum drop more than 12.5 mm (0.5 in) Hg per minute? 

• Disconnect the vacuum line from the vacuum reservoir.

• Connect a hand vacuum pump and apply 508 mm (20 in) Hg of vacuum to the vacuum reservoir.

Does the vacuum drop more than 12.5 mm (0.5 in) Hg per minute? 

• Disconnect the supply vacuum line at the IWE solenoid and allow the system to vent.

• Connect a hand vacuum pump and apply 508 mm (20 in) Hg of vacuum to the vacuum supply line, one-way check valve, and vacuum reservoir.

Does the vacuum drop less than 12.5 mm (0.5 in) Hg per minute? 

• Ignition ON.

• Enter the following diagnostic mode on the scan tool: TCCM Datalogger

• IDS Vehicles: Command IWE_OS # to No. FDRS Vehicles:

  Access the TCCM and control the IWE_OUT_ENGAGED PID

  = No (False)

• Disconnect the IWE solenoid output vacuum line at the IWE solenoid. The vacuum supply line remains connected to the IWE solenoid.

• Connect a vacuum gauge to the IWE solenoid output port.

• Start the engine and let it idle for 2- 5 minutes until vacuum reading stabilizes.

Is the vacuum greater than 254mm (10 in Hg) at the IWE solenoid output port? 

• Ignition OFF.

• Disconnect the IWE solenoid output vacuum line at the IWE solenoid.

• Using a hand vacuum pump, apply 508 mm (20 in) Hg of vacuum to the IWE system through the solenoid output vacuum line.

• Observe the vacuum reading.

Does the vacuum drop more than 12.5 mm-Hg (0.5 in-Hg) per minute? 

• With the vehicle in NEUTRAL, position it on a hoist. REFER to: Jacking and Lifting - Overview .

• Disconnect the vacuum lines from the RHIWE.

• Apply 508 mm (20 in) Hg of vacuum to the larger port on the RHIWE and observe vacuum reading.

Does the vacuum drop more than 12.5 mm-Hg (0.5 in-Hg) per minute? 

• Disconnect the vacuum lines from the LHIWE.

• Apply 508 mm (20 in) Hg of vacuum to the larger port on the LHIWE and observe vacuum reading.

Does the vacuum drop more than 12.5 mm-Hg (0.5 in-Hg) per minute? 

• With the vehicle in NEUTRAL, position it on a hoist. REFER to: Jacking and Lifting - Overview .

• Disconnect the vacuum line at the RHIWE.

• Connect a hand-held vacuum gauge to the larger vacuum supply line at the RHIWE.

• Ignition ON.

• Enter the following diagnostic mode on the scan tool: TCCM Datalogger

• IDS Vehicles: Command IWE_OS # to No. FDRS Vehicles:

  Access the TCCM and control the IWE_OUT_ENGAGED PID

  = No (False)

• Start the engine and let it idle for 2- 5 minutes until vacuum reading stabilizes.

Is the vacuum greater than 254mm (10 in Hg) at the RHIWE? 

• Disconnect the vacuum line at the LHIWE.

• Connect a hand-held vacuum gauge to the larger vacuum supply line at the LHIWE.

• Ignition ON.

• Enter the following diagnostic mode on the scan tool: TCCM Datalogger

• For IDS Vehicles: Command IWE_OS # to No, FDRS Vehicles: Command IWE_OUT_ENGAGED = No (False).

• Start the engine and let it idle for 2- 5 minutes until vacuum reading stabilizes.

Is the vacuum greater than 254mm (10 in Hg) at the LHIWE? 

• Ignition OFF.

• Connect a hand vacuum pump with gauge to the larger port of the RHIWE.

• 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 RHIWE.

Did the RHIWE disengage between 152 and 203 mm (6 to 8 in) Hg and engage when the vacuum is released? 

• Connect a hand vacuum pump with gauge to the larger port of the LHIWE.

• 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 LHIWE.

Did the LHIWE disengage between 152 and 203 mm (6 to 8 in) Hg and engage when the vacuum is released?