Fuel Pump/Oil Pressure Switch

Diagnostic Chart:

Wiring Diagram:

DIAGNOSIS

^ The following tables will diagnose the oil level switch, the oil pressure switch and the coolant level switch circuits.

^ For diagnosis of the fuel pump circuitry portion of the fuel pump and engine oil level switch, refer to Engine Cranks but Does Not Run.

^ For diagnosis of the Instrument Panel Cluster (IPC), refer to Instrument Panel, Gauges and Warning Indicators.

^ For PCM replacement information, refer to PCM/EEPROM Replacement/Programming.

CIRCUIT DESCRIPTION

The fuel pump and engine oil pressure indicator switch has two functions. One is to indicate low engine oil pressure and the other is to supply battery voltage to the fuel pump in the event the fuel pump relay fails.

The oil pressure portion of the switch has normally closed contacts that open when oil pressure is greater than 41 kPa (6 psi). The contacts will close when oil pressure is less than 14 kPa (2 psi). When the contacts are closed, the oil pressure signal is sent to the Powertrain Control Module (PCM). The PCM then sends this signal to the Instrument Panel Cluster (IPC) through to illuminate the oil pressure telltale lamp on the IPC.

The fuel pump portion of the switch has normally open contacts that close when oil pressure is greater than 4 kPa (6 psi). The contacts will open when the oil pressure is less than 14 kPa (2 psi). In the event the fuel pump relay fails, battery voltage is supplied to the fuel pump through the closed contacts.

DIAGNOSTIC AIDS

^ For diagnosis of the fuel pump circuitry portion of the fuel pump and engine oil level switch, refer to Engine Cranks but Does Not Run.

^ 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 Engine Lubrication.

^ 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 Instrument Panel, Gauges and Warning Indicators for Instrument Panel Cluster (IPC) replacement.

19. Replacement PCM's must be reprogrammed. Refer to the latest Techline information for programming procedures.

20. If no faults have been found at this point, refer to Diagnostic Aids for additional checks and information.