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594 Posts
ETA 1-9-2023
Subject vehicle: 1996 Sonoma SLS RWD 2.2L MT Reg cab, 70k miles.
Over ~18 months, as I infrequently worked on this problem, this thread morphed into instructions and a collection of reference photos. Some of my comments and photos in this 1st post did not well support that, so I deleted and/or replaced them. Replies to this post may seem out of place as a result.
This thread contains photos and instructions for investigation and basic repairs related to seam sealer failure in the Cowl Plenum; in and around the Cowl Plenum Drains; and at the vertical hem seams forward of the front door hinges. Removal of all front end sheet metal, excepting the Radiator Support, is addressed.
This was prompted by discovery of rust at the inside, R, front, cab corner, near the bulkhead connector on the subject vehicle. Subsequent investigation determined debris had accumulated in the Cowl Plenum, below the Air Inlet Assembly (behind Glove Box). Possibly 20+ years of moist environment there caused seam sealer failure and rust; allowing a pathway for water from the Cowl Plenum into the Cab interior. Investigation indicates similar may happen at the extreme L side of the Cowl Plenum.
Thread Table of Contents (with hyperlinks)
Subject vehicle: 1996 Sonoma SLS RWD 2.2L MT Reg cab, 70k miles.
Over ~18 months, as I infrequently worked on this problem, this thread morphed into instructions and a collection of reference photos. Some of my comments and photos in this 1st post did not well support that, so I deleted and/or replaced them. Replies to this post may seem out of place as a result.
This thread contains photos and instructions for investigation and basic repairs related to seam sealer failure in the Cowl Plenum; in and around the Cowl Plenum Drains; and at the vertical hem seams forward of the front door hinges. Removal of all front end sheet metal, excepting the Radiator Support, is addressed.
This was prompted by discovery of rust at the inside, R, front, cab corner, near the bulkhead connector on the subject vehicle. Subsequent investigation determined debris had accumulated in the Cowl Plenum, below the Air Inlet Assembly (behind Glove Box). Possibly 20+ years of moist environment there caused seam sealer failure and rust; allowing a pathway for water from the Cowl Plenum into the Cab interior. Investigation indicates similar may happen at the extreme L side of the Cowl Plenum.
Thread Table of Contents (with hyperlinks)
- Post 6 – Accessing the R Cowl Plenum Drain (from exterior)
- Radiator Grille Removal
- Front Bumper Assembly (complete) Removal
- Hood Removal
- R Wheelhouse Removal
- R Fender Removal
- Post 7 – Beginning Instrument Panel (I/P), AKA Dash, Removal
- Defrost Cover Removal
- I/P Speaker Covers Removal
- Post 9 – Continuing I/P Removal
- Supplemental Inflatable Restraint (SIR / Air Bag) Disabling
- L I/P Sound Insulator Removal
- R Door Sill Trim Removal
- R Kick Panel Trim Removal
- R I/P Sound Insulator Removal
- Center Console (manual transmission) Removal
- Center I/P Sound Insulator Removal
- Post 10 – Continuing I/P Removal
- Ash Tray Removal
- Parking Brake Release Handle cable disconnection
- Knee Bolster Removal
- Post 17 – Finishing I/P Removal
- Steering Column Removal
- Antenna Cable disconnection
- I/P-to-Cab fasteners Removal
- I/P HVAC and More Electrical Disconnections
- Post 18 R Cowl Plenum Access (from Cab interior)
- Air (Fresh) Inlet Assembly Removal
- R Cowl Plenum Drain Valve Removal
- Post 19 Accessing the L Cowl Plenum Drain (from exterior)
- L Wheelhouse Removal
- Post 20 Accessing the L Cowl Plenum Drain (from exterior) Continued
- See Post 6 if Radiator Grille, Front Bumper, and Hood not yet removed.
- L Fender Removal
- Post 21 Accessing Cowl Plenum (L and Central Portion)
- Windshield Wiper Arms Removal
- Air Inlet Grille Panel (Center Cowl Panel trim) Removal
- Wiper Transmission Removal
- Post 22 Old Sealer Removal
- Post 23 Rust Removal, Treatment, and Encapsulation
- Post 24 Sealer Application
- Post 25 Optional Top-coat
- Post 26 Beginning Reassembly - Sealing the R Bulkhead Pass-Through
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