Technical Description of OBD-II Trouble Code
Range/Performance Issue with Generator Control Circuit
What does that signify?
This is a generic diagnostic trouble code (DTC) that is applicable to many OBD-II vehicles (1996-newer). This includes vehicles from Ford, Land Rover, Chevrolet, Dodge, GMC, Ram, and others. While it is a generic code, the specific repair steps may vary depending on the year, make, model, and powertrain configuration.
A stored code P065B indicates that the powertrain control module (PCM), or one of the related controllers, has detected an inconsistency in the generator control circuit.
In certain cases, the alternator is referred to as the generator, but this code is more commonly used in hybrid or electric vehicles that generate electrical power from a generator. The generator may be driven by the engine or any of the drive wheels.
Vehicles that use this code route generator supply voltage through the PCM. This means that the battery voltage required to power up the generator field coil (to produce amperage) is supplied only after the PCM has input the appropriate signal to a relay or auxiliary control module. The PCM also monitors generator output voltage and amperage at different RPM levels and load degrees, and calculates voltage requirements accordingly. In addition to monitoring generator output (performance), the PCM is responsible for activating the generator lamp in the event of low output.
If a problem is detected in monitoring the generator control circuit, a code P065B will be stored and a malfunction indicator lamp (MIL) may illuminate.
Example of an alternator (generator):
What is the severity of this DTC?
A P065B should be classified as severe because it may result in a low battery charge level and/or a no start condition.
What are some of the symptoms of the code?
Symptoms of a P065B trouble code may include:
What are some of the common causes of the code?
Possible causes for this code may include:
What are some P065B troubleshooting steps?
Before attempting to diagnose a P065B, ensure that the battery is fully charged and the generator is operating at an acceptable level.
Refer to your vehicle information source for technical service bulletins (TSB) that match the stored code, vehicle details (year, make, model, and engine), and exhibited symptoms. If you find the relevant TSB, it may provide helpful diagnostic information.
To accurately diagnose a code P065B, you will need a diagnostic scanner and a digital volt/ohmmeter. You will also require a reliable source of vehicle information.
Start by connecting the scanner to the vehicle diagnostic port and retrieving all stored codes and freeze frame data. It is advisable to write down this information in case the code proves to be intermittent.
After recording all relevant information, clear the codes and, if possible, test drive the vehicle until the code is reset or the PCM enters readiness mode.
If the PCM enters readiness mode, the code is intermittent and will be even more challenging to diagnose. The condition that caused the P065B to be stored may need to worsen before an accurate diagnosis can be made. Conversely, if the code fails to reset and there are no drivability symptoms, the vehicle can be operated normally.
If the P065B is immediately reset, conduct a visual inspection of the system’s wiring and connectors. Repair or replace any broken or unplugged harnesses as necessary.
If the wiring and connectors appear to be functional, obtain the appropriate wiring diagrams, connector face views, connector pin-out charts, and diagnostic flow charts from your vehicle information source.
Once you have the correct information, test all system fuses and relays to ensure that the generator is receiving voltage.
If generator supply voltage is not present, trace the appropriate circuit back to the fuse or relay from which it originates. Repair or replace any defective fuses, relays, or fusible links as necessary. In some cases, generator supply voltage is routed through the PCM. You can use wiring diagrams and other vehicle-specific information to help diagnose generator voltage supply malfunctions.
If generator supply voltage is present, use your DVOM to test the generator’s output performance at the appropriate pin of the generator connector. If the generator output voltage is not within the specified range, suspect that the generator is defective.
If the generator is charging within specifications, check the voltage level at the appropriate pin of the PCM connector. If the voltage at the PCM connector matches the voltage at the generator, suspect that the PCM is defective or there is a programming error.
If the voltage at the PCM connector differs from the voltage at the generator connector by more than 10 percent, suspect a shorted or open circuit between the two.
