Oil Pressure Diagnosis and Testing

WARNING: This page is about a different car, the 2002 Oldsmobile Bravada, 2002 GMC Envoy XL, 2002 GMC Envoy, and 2002 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.

Tools Required

J 21867 Pressure Gauge
J 25087-C Oil Pressure Tester and Pump Primer

With the vehicle on a level surface, run the vehicle for a few minutes, allow adequate drain down time (2-3 minutes) and measure for a low 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 gauge 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 25087-C.

Fig 1: Removing Oil Filter And Install J 25087-C

Courtesy of GENERAL MOTORS CORP.

Install J 21867 or equivalent to the J 25087-C.
Run the engine and measure the engine oil pressure.
Compare the readings to Engine Mechanical Specifications .
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 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 lash adjusters Repair as necessary
If the 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 vehicle oil pressure gauge or sensor Repair as necessary