GM Service Manual Online
For 1990-2009 cars only

Tools Required

J 23100 Vacuum Modulator Wrench

Notice: Use of another tool to remove the vacuum modulator may result in internal damage to the modulator.


    Object Number: 180636  Size: SH
  1. Using J 23100 remove the vacuum modulator (118) with the O-ring seal and the modulator plunger (116).
  2. Inspect the modulator plunger for nicks, scratches and scoring.

  3. Object Number: 180639  Size: SH
  4. Remove the modulator valve (115), and the modulator valve sleeve (114).
  5. Inspect the modulator valve and sleeve for:
  6. • nicks
    • scratching
    • scoring

Tools Required

    • J 23100 Vacuum Modulator Wrench
    • J 23738-A Hand Operated Vacuum Pump

Removal Procedure

  1. Raise and suitably support the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.

  2. Object Number: 166194  Size: SH
  3. Disconnect the vacuum hose and pipe (1) from the vacuum modulator (2).

  4. Object Number: 166196  Size: SH
  5. Use the J 23100 in order to remove the vacuum modulator (1) and the plunger (3) from the transmission.

Inspection Procedure


    Object Number: 166196  Size: SH
  1. Perform the following procedure in order to inspect the vacuum modulator (1) for leakage:
  2. 1.1. Remove the vacuum modulator plunger (3) from the vacuum modulator (1).
    1.2. Inspect for fluid that drains out of the vacuum modulator (1).
    1.3. Replace the vacuum modulator (1) if transmission fluid is present in the vacuum modulator.
  3. Perform the following procedure in order to use the J 23738-A when inspecting the vacuum modulator for leakage:
  4. 2.1. Attach the J 23738-A to the vacuum fitting on the rear of the vacuum modulator (1).
    2.2. Apply 67 kPa (20 in Hg) of vacuum to the vacuum modulator.
    2.3. Observe the gauge at the top of the J 23738-A .
    2.4. Replace the vacuum modulator (1) if the J 23738-A indicates a vacuum loss.
  5. Inspect the vacuum modulator O-ring (2) for cuts or other damage.
  6. Replace the vacuum modulator O-ring as necessary.