PCM Controlled Warning Lamps Diagnosis

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

Engine Controls Schematics: I/P and Driver Information Display:

CIRCUIT DESCRIPTION
The PCM controlled lamps are powered through the IGN 1 fuse. The PCM energizes the the bulb, LED, or driver information center indicator by supplying a path to ground through the PCM.

Conditions which will illuminate each lamp are as follows:
^ Low Oil Level Lamp - When the ignition is first turned ON, the PCM commands the Low Oil Level Lamp ON for a brief period of time to test the bulb. The PCM also checks the engine oil level using the Engine Oil Level Switch input. The PCM determines whether or not to test for low oil level based on the difference between engine coolant temperature at the last shutdown and engine coolant temperature at start-up. This is to ensure that the oil has drained back into the sump before testing. To test for low oil level at start-up, one of the following conditions must be present:
- If the engine coolant temperature was between 15°C (59°F) and 130°C (266°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 82°C (180°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 10 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 tested.
^ Generator Lamp - The PCM supplies battery voltage to the generator's internal regulator (generator terminal L). When a fault in the Charging System occurs, the internal regulator grounds the L terminal voltage and the PCM commands the generator lamp ON. The PCM will command the generator lamp ON when the following condition(s) are present:
- Engine speed is above 1200 RPM and system voltage is below 10 volts for at least 10 seconds.
- The PCM detects a low voltage condition on the generator's L terminal for at least 10 seconds.
- Engine speed is between 1000 and 1300 RPM and the generator's F terminal duty cycle remains above 95 percent for 60 seconds.
OR
- Engine speed is between 1000 and 1300 RPM and the generator's F terminal duty cycle remains below 5 percent for 30 seconds.
^ Hot Coolant Lamp - The PCM will command the hot coolant lamp on when engine coolant temperature raises above 124°C (255°F). The PCM will turn the hot coolant lamp OFF when engine coolant temperature decreases to below 121°C (248°F).
^ Change Oil Lamp - The PCM commands the Oil Life Monitor lamp On when an oil change is required. The PCM calculates remaining oil life based on total engine revolutions and calculated engine oil temperature for each start-up since the Oil Life monitor was reset.

DIAGNOSTIC AIDS
A PCM controlled lamp ON at all times most likely indicates that a condition is present which requires the attention of the vehicle operator.

Inspect for the following conditions:
^ Poor connection at PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
^ Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, disconnect the PCM and turn the ignition ON. Observe a Digital Multimeter (DMM) connected to the affected PCM output circuit while moving connectors and wiring harnesses related to the PCM output circuit. A change in voltage will indicate the location of the fault.
^ Engine Oil Level Switch circuit: Use the Engine Oil Level Sensor/Switch Diagnosis.

TEST DESCRIPTION
Number(s) below refer to the step number(s) on the Diagnostic Chart.
3. Normally, ignition feed voltage should be present on the output control circuit with the PCM disconnected and the ignition turned ON with the engine OFF.
4. Tests for a shorted component or a short to B+ on the output control circuit. Either condition would result in a measured current of over 1.5 amps. Also tests for a component that is going open while being operated, resulting in a measured current of 0 amps.
5. Tests for a malfunctioning instrument cluster.
16. 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.