Diagnosis
Use the following diagnostic table to diagnose the generator F and L circuit.
Use the following scan tool parameters when diagnosing the Powertrain Control Module (PCM) controlled generator.
Generator PWM - Range 0-100 Percent: The generator F terminal is a pulse width modulated (PWM) duty cycle or load input to the PCM from the generator. As the generator load increases, the PCM can sense the change and adjust the idle speed accordingly.Generator L Terminal - Range Inactive/Active: The generator L terminal indicates whether the PCM is allowing the generator to operate. The PCM can disable the generator under certain conditions in order to ease starting. Active indicates that the PCM is allowing generator operation, while inactive indicates that the PCM is not allowing generator operation.
Circuit Description
The generator communicates to the Powertrain Control Module (PCM) over two lines, the L or lamp circuit and the F or Field circuit. The PCM uses the L circuit to monitor faults in the charging system. The F circuit is used by the PCM to monitor the duty cycle or load of the generator. The PCM will adjust the idle speed according to the generator load.
Diagnostic Aids
| • | If the generator terminal F input circuit is shorted to voltage, the volts telltale lamp will operate normally. However, the scan tool Generator PWM will display a generator duty cycle near 10%. Check the generator terminal F input circuit for a short to voltage. If OK, the generator may be faulty, refer to the Charging System Check in Engine Electrical. |
| • | An Intermittent problem may be caused by a poor connection, rubbed through wire insulation, or a wire that is broken inside the insulation. |
| • | Any circuitry, that is suspected as causing the intermittent complaint, should be thoroughly checked for the following items: |
| - | Improper mating |
| - | Broken locks |
| - | Poor terminal to wiring connections |
| - | Physical damage to the wiring harness |
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
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The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored on the scan tool for later reference.
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If the volts telltale lamp is not operating, either a short circuit or the IPC is at fault. This determines whether the L circuit, generator or IPC is at fault.
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If the charging system is not functioning, system voltage cannot be maintained above 12 V. Turning off all accessories assures that the system voltage is not being drawn down by an accessory that normally draws a large current.
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Refer to Section 8C1 for replacement of the IPC.
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When the engine is not running, the generator duty cycle will be displayed above 5%. If the generator duty cycle reads 0%, then the field circuit is either open or shorted to ground.
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If the lamp circuit is not shorted to ground, the volts telltale lamp will go OFF until the next key cycle when the test light is probed into terminal B. Be careful not to probe terminal C with the test light, this will turn off the volts telltale lamp whether or not the lamp circuit is shorted.
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The PCM supplies a voltage to the generator. If voltage is available to the generator at this terminal, then the PCM and wiring are OK.
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Replacement PCM's must be reprogrammed. Refer to the latest Techline information for programming procedures.
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If no faults have been found at this point, refer to Diagnostic Aids for additional checks and information.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to | ||
2 | Turn the ignition switch ON, with the engine OFF. Is the volts telltale lamp on the IPC illuminated? | -- | ||
3 | Start the engine. Did the volts telltale lamp on the IPC turn OFF? | -- | ||
Is the volts telltale lamp illuminated on the IPC? | -- | |||
With the accessories OFF, install a scan tool. Does the voltage read greater than the specified value? | 12V | |||
6 | With a test light connected to a ground, probe the lamp signal terminal of the generator electrical connector. Does the test light illuminate? | -- | ||
Replace the Instrument Panel Cluster (IPC). Is the action complete? | -- | -- | ||
Does the GEN F value read greater than the specified value? | 5% | |||
Does the test light illuminate? | -- | |||
10 | Repair the short to voltage in the lamp circuit. Is the action completed? | -- | -- | |
11 | Replace the generator. Refer to Section 6D3 . Is the action complete? | -- | -- | |
12 |
Does the test light illuminate? | -- | ||
13 | Repair the short to ground in the lamp circuit. Is the action complete? | -- | -- | |
With a DVM connected to ground, again probe the lamp signal terminal of the generator electrical connector. Does the DVM read greater than the specified value? | 4.5V | |||
15 | Repair the short to ground in the field circuit. Is the action completed? | -- | -- | |
16 | Repair the poor connection or open circuit in the field circuit. Is the action completed? | -- | -- | |
17 | With the DVM still connected to a ground, probe the battery terminal to the generator. | B+ | ||
18 | Check for a poor connection or an open in the lamp circuit and repair as necessary. Was a repair necessary? | -- | ||
19 | Repair the open or poor connection in the generator battery terminal circuit. Is the action completed? | -- | -- | |
Replace the PCM. Is the action completed? | -- | -- | ||
Operate vehicle within the conditions under which the original symptom was noted. Does the system now operate properly? | -- | System OK Refer to Diagnostic Aids |
