The oil level switch is a magnetic reed float style switch which is closed with oil level full and open when oil level is low. The PCM monitors the oil level switch to determine if the oil is LOW or OK. When the test conditions have been met the PCM will monitor the oil level switch input. If a low oil level is indicated the PCM will send a serial data message to the IPC. The IPC will then indicate the oil level is low. If the test conditions have not been met then the PCM ignores the oil level switch input and oil level OK is indicated to the IPC. The test conditions include a timer and a coolant temperature value. The test conditions are needed to ensure the engine has been OFF long enough for oil to drain back into the oil pan.

The CHANGE ENGINE OIL message is triggered by the Oil Life Left index. When the Oil Life Left index drops to 0 percent, the Change Engine Oil message will appear to the driver. The Oil Life Left index is calculated by the PCM and stored in the EEPROM (see EEPROM ) of the PCM. The PCM uses coolant temperature, engine speed, and vehicle speed to calculate the index. After an oil change, the index may be reset by displaying the Oil Life Left index and then pressing and holding the Reset button on the IPC for approximately 5 seconds or by using the scan tool. When the value is reset, 100 percent Oil Life Left will be displayed.

The PCM calculates a Transaxle Fluid Life Index using transaxle temperature and engine state, running or OFF. The Transaxle Fluid Life Index represents the remaining useful transaxle fluid life as a percentage of total life. When transaxle fluid life reaches 0 percent, the CHANGE TRANS FLUID message will appear. The Transaxle Fluid Life Index can be reset using the Reset button on the IPC.

The PCM will also request messages be displayed when certain DTCs are set. These messages can include the following: