Error Code P065B is defined as Generator Control Circuit Range/Performance. This is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system, particularly those made since 1996 up to present. This includes models from, but not limited to Chrysler, Dodge, Ford, GMC, Land Rover, etc. Specifications on the definition, troubleshooting, and repairs, of course, vary from make, model, and powertrain configuration.
When this code is present, that means the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes), or one of the related controllers, has determined a discrepancy in the generator control circuit.
In some cases, the alternator is referred to as the generator. More frequently, this type of setup is used for hybrid or electric vehicles that generate electrical power from a generator. The generator may be driven by the engine of any of the drive wheels.
Vehicles that use this type of code route generator supply voltage through the PCM. This means the battery voltage needed to power up the generator field coil (to produce amperage) is supplied only after the PCM has input the right signal to a relay or auxiliary control module. The PCM also monitors the generator output voltage and amperage at varying RPM levels and load degrees, and calculate the voltage requirements. Aside from monitoring the output of the generator (performance), the PCM also provides a signal to activate the generator lamp in the event of low output.
If a fault in monitoring the generator control circuit has been detected, then the Error Code P065B will be stored, activating the Check Engine light.
When this code appears, the problem is considered severe, as it may result in low battery charge level, which leads to no start condition. Thus, common symptoms would include:
- Delayed or no start
- Inoperative electrical accessories
- Engine drivability problem
Common causes for this code include:
- Defective generator
- Open or shorted circuit between the PCM and generator
- Faulty fusible link, fuse, or relay
- Faulty PCM of controller
- Programming error in PCM
How to Check
The battery must be fully charged, while the generator must be at an acceptable level before attempting to diagnose this code.
As with most codes, the best way to start the diagnosis for this code is to check with the TSB (Technical Service Bulletins) and replicate the codes stored. Look for the same symptoms of the same year, make, model, and engine. Finding the right TSB usually leads to helpful diagnostic information.
Diagnostic scanner and DVOM (digital volt/ohmmeter) will also be necessary for more accurate diagnosis.
Start the diagnosis by connecting the scanner to the vehicle’s diagnostic port. Retrieve all stored codes and freeze frame data. You will want to take note of the code just in case they’re proven to be intermittent.
After recording all pertinent information, clear the codes and then take the vehicle for a test drive (if applicable) and see if the code resets, or the PCM enters readiness mode.
If the PCM enters readiness mode, that means the problem is intermittent. You may have to wait for the problem to worsen before you can accurately diagnose it. If the code does NOT reset, however, and there are no drivability symptoms, you can run the vehicle normally.
On the other hand, if the code resets, then you can proceed for a thorough inspection of the system and all its related wirings and connectors. Broken or unplugged harnesses must be repaired or replaced, as necessary.
If the connectors and wirings look functional, then use the vehicle information to obtain the right wiring diagram, connector pin-out charts, connector face views, and diagnostic flow charts. Once you have the right information, then test all the system fuses and relays and make sure the generator is being properly supplied with voltage.
If there is no voltage supply present, then trace the right circuit back to the fuse or relay from which it comes from. Look for signs of damage such as defective fuses, relays, or fusible links. Repair as necessary.
In some vehicle makes and models, the generator supply voltage is routed through the PCM. With this, you may use wiring diagrams and other vehicle-specific information to help diagnose generator voltage supply malfunctions.
If there is a generator supply, then use your DVOM to test the generator output performance at the right pin of the generator connector. If the right level of generator output voltage could not be found, then you can suspect a defective generator.
If the generator is charging within specifications, then check the level of voltage at the right pin of the PCM connector. If the generator shows the same voltage at the PCM connector, then you can suspect a defective PCM or a programming error in the PCM.
If the voltage at the PCM connector differs (by more than 10%) between what is read at the generator connector, then you can suspect an open or shorted circuit between the two.
How to Fix
Depending on your diagnosis, common repairs for this code include:
- Replacement of the faulty generator
- Repair or replacement of faulty fuse, relay, or fusible link
- Repair or replacement of open or shorted circuit between the generator and PCM
- Repair of faulty PCM
- Reprogramming of PCM
To avoid misdiagnosis, the generator fuses must be tested with the circuit loaded.
As said earlier, this code is a serious problem which can hinder the vehicle’s drivability performance or keep the vehicle from starting. Thus, it must be addressed as soon as possible.