Hydraulic System Inspection

HYDRAULIC SYSTEM INSPECTION

Required Special Tools:

- MB991958: M.U.T.-III Sub Assembly
- MB991824: Vehicle Communication Interface (V.C.I.)
- MB991910: M.U.T.-III Main harness A

The convertible top is operated by hydraulic pressure. A hydraulic pump pressurizes lines carrying hydraulic fluid to the cylinders move the top open and close, based on the amount of pressure exerted on the cylinders during top operation. Hydraulic fluid flow moves a piston inside each cylinder, to extend or retract it. The cylinder movement raises or lowers a section of the top of the tonneau cover.

HYDRAULIC SYSTEM DIAGNOSIS





1. Visually inspect the convertible top as follow.
(1) Remove the tonneau latch cover, drain trough assembly and upper cover. Check the position of the manual valve. (If the manual valve is not closed, top operation will be slow or disabled.) If the valve is open, close the valve and retry convertible top operation. If the top now operates property, do not continue with this procedure.
(2) Check for any bent control link or damaged hinges. Replace damaged components as necessary.
(3) Check for kinked hydraulic lines. Replace damaged lines as necessary.
(4) Inspect for hydraulic fluid leakage at the system lines and components. If any leakage is evident, replace any leaking components.
2. Operate the convertible top and listen to the sound of the hydraulic pump operation.
If necessary, listen to a known good system on another vehicle to compare the sound of the hydraulic pump operation.
If the pump operates with an excessively high-pitched noise, there may be a hydraulic leak. If the pump operates with an excessively low-pitched noise, there may be a restriction in a hydraulic line. Note the sound of the pump operation, then continue with Step 3.









3. Check hydraulic fluid level as follows.
(1) With the tonneau latch cylinder in the open (extended) position as show, lift the tonneau cover and lift the No. 5 bow to the vertical.
(2) Check the hydraulic fluid level in the hydraulic pump reservoir. The hydraulic fluid should be between the MAX and MIN marks.
(3) Drain or replenish the hydraulic fluid as necessary to achieve proper fluid level.
4. The convertible top control module must re-establish convertible top position. To do this, system must be reset as follow.
(1) Manually open the convertible top to the fully open position (Refer to Procedures).
(2) Close the tonneau.
(3) Close all doors and windows.
(4) Manually close the convertible top to the fully closed position. As the top moves, check for any jerky or uneven movement. Also check the movement of the hydraulic cylinder.
(5) If any hydraulic cylinder does not fully extend or retract, possible causes are cylinder leakage, an external hydraulic leak, a hydraulic line restriction, or mechanical binding. Replace the affected component(s).
5. Connect the scan tool MB991958 to check for any DTCs.
(1) Note the DTCs and then clear them.
(2) If one or more convertible top DTCs are set (DTC B1301 to 1340 or DTC U1073), refer to the appropriate DTC diagnosis ( Convertible Top).
(3) If no convertible top DTCs (DTC B1301 to 1340 or DTC U1073) are set, continue with Step 6.





6. The hall sensors on the hydraulic cylinders identify the position of the piston in the No. 5 bow cylinders and No. 5 bow lock cylinders, the tonneau latch cylinder, and the tonneau cylinder.
Check for any damage to the hall sensors or their wires. Repair or replace as necessary.
If any metallic debris is present on a hall sensor, remove the debris, then retry top operation.





7. Check the hydraulic pump motor operation as follows.
(1) Open the tonneau cover and the No. 5 bow.
(2) Install an inductive clamp on an ammeter. Then connect the clamp to the ground wire of the motor.
(3) Operate the convertible top and observe the amp reading on the meter as the top is opened and closed.
(4) The amperage should peak at approximately 24 to 30 A during top operation.
(5) If the amperage peak is lower than 24 A, install Chassis Ears at the hydraulic lines at each cylinder, one at a time. Listen for an aeration sound that indicates hydraulic fluid bypassing a seal in a cylinder. Replace the affected cylinder.

- If an aeration sound is heard, replace the affected cylinder. (If leakage is determined at a No. 5 bow cylinder, No. 5 bow locking cylinder, or main rotary cylinder, replace the affected cylinders on both sides.)
- If no aeration sound is heard, replace the hydraulic pump.
(6) If the amperage peak is higher than 30 A, first confirm that there are no kinks in the hydraulic lines. If not, there is an internal pump failure. Replace the hydraulic pump.
8. Verify proper convertible top operation.