Circuit Description
The PCM controlled lamps are powered through the IGN 1 fuse. The PCM energizes the the bulb or 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 startup. This is to ensure that the oil has drained back into the sump before testing. To test for low oil level at startup, 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 termperature 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 termperature was higher than 100°C (212°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 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. |
| - | If DTC P0560 is set, refer to DTC P0560 System Voltage . |
| • | Second Gear Lamp (4L60E Transaxle Only) - The PCM supplies 12 volts to the second gear start switch through a pull-up resistor. The second gear start switch is a normally open switch. The PCM senses a high input voltage, commands normal transaxle shifting, and the second gear start lamp is not illuminated. When the second gear start switch is closed, the input voltage to the PCM is pulled low. The PCM turns the second gear lamp ON and commands the to vehicle begin in second gear (the following gears shift in normal sequence). |
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 Sensor and/or Switch Diagnosis . |
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Chart.
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Normally, ignition feed voltage should be present on the output control circuit with the PCM disconnected and the ignition turned ON.
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Checks 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 checks for a component that is going open while being operated, resulting in a measured current of 0 amps.
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Checks for a faulty instrument cluster.
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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.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
2 | Was the Instrument Cluster System Check in Electrical Diagnosis performed? | -- | Go to the Instrument Cluster System Check in Electrical Diagnosis | |
Is voltage near the specified value? | B+ | |||
Does the current reading remain between the specified value? | 0.002-0.5 amps 2-500 mA | |||
Is voltage at the specified value? | 0 V | |||
6 | Locate and repair the short to voltage in the affected lamp control circuit. Refer to Wiring Repairs . Is action complete? | -- | -- | |
7 | Check the ignition positive voltage feed fuse for the instrument cluster indicator lamps. Is the the fuse open? | -- | ||
8 |
Is action complete? | -- | -- | |
9 |
Is voltage near the specified value? | B+ | ||
10 |
Was a problem found? | -- | ||
11 |
Was a problem found? | -- | ||
12 |
Does the test light flash ON and OFF? | -- | Go to Diagnostic Aids | |
13 |
Was a problem found? | -- | ||
14 | Locate and repair open in the ignition positive voltage circuit to the instrument cluster indicator lamps. Refer to Wiring Repairs . Is action complete? | -- | -- | |
15 | Replace the instrument cluster. Refer to On-Vehicle Service in Instrument Panel, Gages, and Console. Is action complete? | -- | -- | |
Replace the PCM. Important: The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Is action complete? | -- | -- | ||
17 | Operate the affected lamp control circuit using the scan tool output tests function. Does the affected lamp control circuit operate properly? | -- | System OK |
