Circuit Description
The powertrain control module (PCM) uses the generator turn ON the 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 10-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 10-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.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P1637 Charging System Lamp Control Circuit.
Conditions for Running the DTC
| • | The ignition is ON. |
| • | System voltage between 9-18 volts. |
Conditions for Setting the DTC
| • | An improper voltage level has been detected on the generator L-terminal circuit. |
| • | The above conditions are present for at least 30 seconds. |
Action Taken When the DTC Sets
The PCM stores conditions which were present when the DTC set as Failure Records only. This information will not be stored as Freeze Frame Records.
Conditions for Clearing the MIL/DTC
| • | The DTC becomes history when the conditions for setting the DTC are no longer present. |
| • | The history DTC clears after 40 malfunction free warm-up cycles. |
| • | The PCM receives a clear code command from the scan tool. |
Step | Action | Value | Yes | No |
|---|---|---|---|---|
Schematic Reference: Starting and Charging Schematics Connector End View Reference: Engine Electrical Connector End Views | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |
2 |
Does the scan tool indicate that DTC P1637 has passed? | -- | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 3 |
3 |
Does the voltage measure near the specified value? | 10 V | Go to Step 5 | Go to Step 4 |
4 | Test the generator turn on signal circuit for a short or open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 8 | Go to Step 6 |
5 | Inspect for poor connections at the harness connector of the generator. Refer to Connector Repairs . Did you find and correct the condition? | -- | Go to Step 8 | Go to Charging System Test |
6 | Inspect for poor connections at the harness connector of the powertrain control module (PCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 8 | Go to Step 7 |
7 | Replace the PCM. Refer to Control Module References for replacement, setup, and programming. Is the action complete? | -- | Go to Step 8 | -- |
8 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
