PCM Controlled Warning Lamps Diagnosis

Diagnosis

^ The following table will diagnose the oil pressure switch.
^ For diagnosis of the Body Function Controller, refer to the Electrical Diagnosis.
^ Replacement PCMs must be reprogrammed and the crankshaft position system variation procedure must be be performed. Refer to the latest Techline information for PCM programming and the Powertrain Control Module for the Crankshaft Position System Variation Procedure. Testing and Inspection

Engine Oil Pressure

The scan tool displays oil pressure as Low or OK. The PCM checks the engine oil pressure continuously. If the oil pressure switch indicates low oil pressure at any time, the PCM will send information through serial data to the Body Function Controller (BFC) to turn ON the Low Oil Pressure telltale located on the Instrument Panel Cluster (IPC).

Diagnostic Aids

^ Low oil level or low oil pressure at times may be caused by an engine mechanical problem. If a low oil pressure problem is suspected, refer to the Engine Mechanical.
^ An Intermittent problem may be caused by a poor connection, rubbed through wire insulation, or a wire that is broken inside the insulation.
^ Any circuitry, that is suspected as causing the intermittent complaint, should be thoroughly checked for the following conditions:

- Backed out terminals
- Improper mating
- Broken locks
- Damage to the wiring harness

Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored on the scan tool for later reference.
2. This step is crucial to prevent possible engine damage due to a low oil condition.
7. The PCM senses when the oil pressure signal is pulled low by the oil pressure switch. This step will determine if the PCM is able to sense the signal.
8. When the oil pressure is low, the signal circuit is grounded through the oil pressure switch. This step will determine if the signal is grounded because of the oil pressure switch or a short to ground.
9. The PCM uses a voltage signal to sense when the oil pressure circuit is pulled low. This step will determine if battery voltage was on this circuit normally or because of a short. When the signal circuit is probed by a test light connected to ground, the oil pressure symbol will illuminate
15. If an oil pressure problem is suspected, do not run the engine longer than necessary to avoid possible internal engine damage.
16. Refer to the Body Function Controller for BFC diagnosis.
19. Replacement PCMs must be reprogrammed and the crankshaft position system variation procedure must be be performed. Refer to the latest Techline information for PCM programming and the Powertrain Control Module for the Crankshaft Position System Variation Procedure. Testing and Inspection
20. If no malfunction have been found at this point, refer to Diagnostic Aids for additional checks and information.