This is per Alldata for my 1997 Bonneville...
The engine oil level switch is a float switch that is grounded when the engine oil level is OK. The PCM checks engine oil level at start-up. Before checking the state of the engine oil level switch, the PCM performs a test routine based on time and engine coolant temperature to ensure that the engine oil has drained back into the sump. To test for low oil level at start-up, one of the following conditions must be present:
- If the engine coolant temperature was between 151°C (59°F) and 140°C (284°F) at the last key OFF, the engine coolant temperature at key ON must be at least 12°C (22°F) cooler than the engine coolant temperature at the last key OFF.
- If the engine coolant temperature was higher than 140°C (284°F) at the last key OFF, the time between last key OFF and the present key ON must be sufficient to allow the oil to drain back to the sump. The PCM will remain powered up for 15 seconds to ensure that the oil has drained back to the sump. If the key is turned back ON while the PCM is still powered up, the oil level will not be checked.
The low engine oil level lamp will be illuminated for about a minute when the PCM checks for low oil level and the engine oil level switch indicates that a low oil level condition exists (engine oil level switch circuit not grounded). When the ignition is first turned ON, the PCM commands the low engine oil level lamp ON for a brief period of time to test the bulb.
For diagnosis of the instrument panel, refer to the Instrument Panel
Check for the following conditions:
- Poor connection at the PCM or the engine oil level switch.
Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
Inspect the wiring harness for damage. If the harness appears to be OK, disconnect the PCM and turn the ignition ON. Observe a voltmeter connected to the affected PCM output circuit while moving connectors and wiring harnesses related to the engine oil level switch. A change in voltage will indicate the location of the fault.
- Low engine oil level lamp control circuit.
If a problem with the low engine oil level lamp can not be isolated using the Engine Oil Level Switch diagnostic table, refer to PCM Controlled Warning Lamps Diagnosis. See: PCM Controlled Warning Lamps Diagnosis
Number(*) below refer to the step number(*) on the Diagnostic Chart.
- This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.