Circuit Description
The powertrain control module (PCM) uses the generator turn on signal circuit to control the generator. A high side driver within the PCM allows the PCM to turn the generator ON and OFF. When generator operation is desired, the PCM sends a 5 volt signal to the voltage regulator via the generator turn on signal circuit. This causes the voltage regulator to begin controlling the generator field circuit. Once the generator is enabled by the PCM, the voltage regulator controls generator output independently of the PCM. Under certain operating conditions, the PCM can turn Off the generator by turning Off the 5 volt signal on the generator turn ON signal circuit. The PCM has fault detection circuitry which monitors the state of the generator turn ON signal circuit. If the fault detection circuit senses a voltage other than what is expected, this DTC will set. The voltage regulator also contains fault detection circuitry. If the regulator detects a problem, the regulator will ground the generator turn on signal circuit, pulling the voltage low. This also causes the PCM to set the DTC.
The PCM receives generator output feedback via the generator field duty cycle signal circuit. The voltage regulator generates a pulse width modulation (PWM) signal on the field control circuit. The regulator varies the pulse width of this signal in order to control generator output. This signal is also sent to the PCM via the generator field duty cycle signal circuit. The pulse width of the signal is proportional to generator output. The PCM expects generator output to be within a predetermined range under certain operating conditions. If the PCM detects that the PWM signal on the generator field duty cycle signal circuit is not within the expected range, this DTC will set.
When this DTC sets, the PCM sends a class 2 serial data message to the IPC illuminating the Charge indicator lamp.
Conditions for Running the DTC
The engine is running.
Conditions for Setting the DTC
| • | The generator turn on signal circuit voltage is low while the PCM is commanding the generator ON. |
| • | The above condition is present for more than 30 seconds. |
OR
| • | The generator field duty cycle signal PWM is less than 5 percent. |
| • | The engine RPM is less than 2,500. |
| • | The above conditions are present for more than 30 seconds. |
Action Taken When the DTC Sets
| • | The PCM stores the DTC information into memory when the diagnostic runs and fails. |
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | A history DTC will clear after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic. |
| • | The current DTC will clear when the diagnostic runs and does not fail. |
| • | Use a scan tool in order to clear the MIL diagnostic trouble code. |
Step | Action | Value | Yes | No |
|---|---|---|---|---|
Schematic Reference: Starting and Charging Schematics Connector End View Reference: Master Electrical Component List in Wiring Systems | ||||
1 | Did you perform the Engine Electrical Diagnostic System Check? | -- | Go to Step 2 | |
2 |
Does the scan tool indicate that DTC P0620 has passed this ignition cycle? | -- | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | Go to Step 3 |
3 |
Does the scan tool indicate that the GEN - F Terminal parameter is greater than specified value? | 10% | Go to Step 4 | Go to Step 5 |
4 | With the scan tool command the generator L-Terminal OFF. Is the GEN - F Terminal less than the specified value? | 10% | Go to Step 7 | Go to Step 5 |
5 |
Is the voltage equal to the first value with the generator OFF and equal to the second value with the generator ON? | 0.0 V 5.0 V | Go to Step 6 | Go to Step 10 |
6 |
Is the GEN - F Terminal display affected? | -- | Go to Step 12 | Go to Step 11 |
7 |
Is the voltage equal to the specified value? | 12 V | Go to Step 8 | Go to Step 9 |
8 | Test the battery positive voltage circuit of the generator for a high resistance or open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 12 |
9 | Test the generator sense circuit for a high resistance or open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 12 |
10 | Test the generator turn on signal circuit for a short or open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 13 |
11 | Test the generator field duty cycle signal circuit for a short or open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 13 |
12 | Inspect for poor connections at the harness connector of the generator. Refer to Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 15 | Go to Charging System Test |
13 | Inspect for poor connections at the harness connector of the PCM. Refer to Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 14 |
14 |
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls - 3.8L. Is action complete? | -- | Go to Step 15 | -- |
15 |
Does the scan tool indicate that DTC P0620 failed this ignition? | -- | Go to Step 3 | System OK |
