Oil Pressure Diagnosis and Testing

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2003 GMC Yukon XL, 2003 GMC Yukon, 2003 Chevrolet Tahoe, 2003 Chevrolet Suburban, and 2003 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.

Tools Required

J 21867 Pressure Gage
J 42907 Oil Pressure Testing Tool

Fig 1: Installing Oil Pressure Testing Tool (J 42907) & Pressure Gage (J 21867)

Courtesy of GENERAL MOTORS CORP.

With the vehicle on a level surface, run the vehicle for a few minutes. Allow adequate drain down time, 2-3 minutes, and measure the oil level.
If required, add the recommended grade engine oil and fill the crankcase until the oil level measures full on the oil level indicator.
Run the engine briefly, 10-15 seconds, and verify low or no oil pressure on the vehicle gage or light.
Listen for a noisy valve train or a knocking noise.
Inspect for the following:
- Oil diluted by water or glycol anti freeze
- Foamy oil
Remove the oil filter and install the J 42907 .
Install J21867 or equivalent to the J42907 .
Run the engine and measure the engine oil pressure.
Compare the readings to Engine Mechanical (4.8L, 5.3L, And 6.0L) Specifications (LR4 VIN V) or Engine Mechanical (4.8L, 5.3L, And 6.0L) Specifications (LM7 VIN T) or Engine Mechanical (4.8L, 5.3L, And 6.0L) Specifications (L59 VIN Z) or Engine Mechanical (4.8L, 5.3L, And 6.0L) Specifications (LQ4 VIN U) or Engine Mechanical (4.8L, 5.3L, And 6.0L) Specifications (LQ9 VIN N) .
If the engine oil pressure is below specifications, inspect the engine for one or more of the following:
- Oil pump worn or dirty
  Refer to Oil Pump Cleaning and Inspection .
- Oil pump-to-engine block bolts loose
  Refer to Oil Pump, Pump Screen and Deflector Installation .
- Oil pump screen loose, plugged, or damaged
- Oil pump screen O-ring seal missing or damaged
- Malfunctioning oil pump pressure regulator valve
- Excessive bearing clearance
- Cracked, porous, or restricted oil galleries
- Oil gallery plugs missing or incorrectly installed
  Refer to Engine Block Plug Installation .
- Broken valve lifters
  Repair as necessary.
If the oil pressure reading on the J 21867 or equivalent is within specifications, inspect for the following:
- Plugged or incorrect oil filter and/or malfunctioning oil bypass valve
- Malfunctioning oil pressure gage or sensor
  Repair as necessary.