P065B Generator Control Circuit Range/Performance

Description and meaning of DTC p065b

This is a generic diagnostic trouble code (DTC) and applies to many OBD-II vehicles (1996-newer). That may include but is not limited to vehicles from Ford, Land Rover, Chevrolet, Dodge, GMC, Ram, etc. Although generic, the exact repair steps may vary depending on year, make, model, and powertrain configuration. A stored code P065B means that the powertrain control module (PCM), or one of the other related controllers, has detected a discrepancy in the generator control circuit. In some cases, the alternator is called the generator but more frequently this type of code is used in a hybrid or electric vehicle which generates electrical power from a generator. The generator may be driven by the engine or any of the drive wheels. Vehicles which utilize this type of code route generator supply voltage through the PCM. This means that the battery voltage that is required to power up the generator field coil (so that it can 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 varying RPM levels and load degrees and calculates voltage requirements accordingly. In addition to monitoring generator output (performance), the PCM is responsible for providing a signal that activates 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 be illuminated.

p065b diagnostic trouble code symptoms

Symptoms of a P065B trouble code may include:Delayed or no startElectrical accessories may be inoperativeEngine drivability issues

DTC p065b - possible causes

Causes for this code may include:Defective generatorBad fuse, relay, or fusible linkOpen or shorted circuit between the PCM and generatorPCM programming errorFaulty controller or PCM

How to fix OBD-II diagnostic trouble code p065b

The battery must be fully charged and the generator operating at an acceptable level before attempting to diagnose a P065B. Consult your vehicle information source for technical service bulletins (TSB) that replicate the code stored, vehicle (year, make, model, and engine), and symptoms exhibited. If you find the appropriate TSB, it may yield helpful diagnostic information. A diagnostic scanner and a digital volt/ohmmeter will be necessary to accurately diagnose a code P065B. A reliable source of vehicle information will also be required. Begin by connecting the scanner to the vehicle diagnostic port and retrieving all stored codes and freeze frame data. You will want to write this information down, just in case the code proves to be an intermittent one. After recording all pertinent information, clear the codes and test drive the vehicle (if possible) 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 difficult to diagnose. The condition, which caused the P065B to be stored, may need to worsen before an accurate diagnosis can be reached. On the other hand, if the code fails to reset and there are no drivability symptoms exhibited, the vehicle can be operated normally. If the P065B is immediately reset, proceed with a visual inspection of system related wiring and connectors. Harnesses that have been broken of unplugged should be repaired or replaced as required. If wiring and connectors appear functional, use your source of vehicle information to obtain the appropriate wiring diagrams, connector face views, connector pin-out charts, and diagnostic flow charts. Once you have the correct information, test all system fuses and relays to make sure the generator is being supplied 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 defective fuses, relays, or fusible links as required. In some cases generator supply voltage is routed through the PCM. You may 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 generator output performance at the appropriate pin of the generator connector. If the appropriate level of generator output voltage is not discovered, suspect that the generator is defective. If the generator is charging within specifications, check the level of voltage at the appropriate pin of the PCM connector. If the voltage is the same at the PCM connector as it is at the generator, suspect that the PCM is defective or there is a programming error. Should the level of voltage at the PCM connector differ (by more than 10-percent) between what is detected at the generator connector, suspect a shorted or open circuit between the two. Generator fuses should be tested with the circuit loaded to avoid a misdiagnosis

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