PCM Controlled Warning Lamps Diagnosis
CIRCUIT DESCRIPTION
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 will be illuminated for about a 1 minute afier the ignition has been turned ON when the PCM tests 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). 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. 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. 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 remian 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 tested.
^ Charge 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.
^ Hot Coolant Lamp -The PCM will command the hot coolant lamp ON when engine coolant temperature rises 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 will command the Change Oil lamp ON when the PCM determines the oil life has reached its maximum.
^ Fuel Level Gauge -The PCM controls the fuel level gauge by using inputs to the PCM from the Fuel Level Sensor in the fuel tank.
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.
Check 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 voltmeter 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 Switch Diagnosis. 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.
4. Checks for a shorted component or a short to battery positive voltage on the output control circuit. Either condition would result in a measured current of over 1.5 amps. Also checks for a component that is going open while being operated, resulting in a measured current of 0.0 amps.
5. Checks 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.