What does it mean?
This is a generic diagnostic trouble code (DTC) and applies to many OBD-II vehicles (1996-newer). This may include, but is not limited to, Acura, Buick, Chevrolet, Chrysler, Dodge, Ford, GMC, Hyundai, Kia, Honda vehicles, etc. Although generic, the exact repair steps may vary depending on the year, make, model, and powertrain configuration.
A stored P0648 code means that the Powertrain Control Module (PCM) has detected a malfunction in the immobilizer lamp control circuit.
The immobilizer lamp is located in the instrument panel. Its main function is to warn the driver that the immobilizer key has malfunctioned or is not recognized (when lit). This warning lamp is sometimes called the security lamp.
The PCM typically monitors the continuity of the immobilizer lamp control circuit whenever the ignition is turned on. The immobilizer key is equipped with a transponder that is recognized by the PCM (and other controllers) when it is in close proximity to the vehicle. This allows various systems (such as push-button start and keyless entry) to remain functional and convenient.
Whenever the ignition is turned on and the PCM is powered up, several controller self-tests are performed. In addition to running internal controller self-tests, the Controller Area Network (CAN) carries serial data from each individual module to ensure that the onboard controllers interface correctly.
If a problem is detected in the monitoring of the immobilizer lamp control circuit, a P0648 code will be stored and a Malfunction Indicator Lamp (MIL) may be illuminated.
A typical immobilizer lamp:
P0648 Immobilizer Lamp
How serious is this DTC?
Internal control module codes should be taken seriously. A stored P0648 code (with the immobilizer lamp illuminated) will likely result in a no-start condition.
What are some of the symptoms of the code?
Symptoms of a P0648 trouble code may include:
No start
Inoperative immobilizer lamp
Other (security) codes stored
What are some of the common causes of the code?
Causes
of this code may include:
Faulty PCM
PCM programming error
Open or shorted immobilizer lamp control circuit
Faulty immobilizer key (fob) (dead battery)
Faulty immobilizer lamp bulb
What are the P0648 troubleshooting steps?
A diagnostic scanner, a digital volt/ohmmeter (DVOM), and a reliable source of vehicle information will be needed to diagnose a P0648 code.
Consult your vehicle information source for Technical Service Bulletins (TSBs) that match the stored code, the vehicle (year, make, model, and engine), and the symptoms presented. If you find the appropriate TSB, it may provide helpful diagnostic information.
Start by connecting the scanner to the vehicle’s diagnostic port and retrieving all stored codes and freeze frame data. You will want to note this information, just in case the code proves to be intermittent. After recording all relevant information, clear the codes and test drive the vehicle until the code resets or the PCM enters readiness mode.
If the PCM enters readiness mode, the code is intermittent and will be more difficult to diagnose. The condition that caused the P0648 to be stored may need to worsen before an accurate diagnosis can be made. If the code resets, continue with your diagnosis.
Use your vehicle information source to obtain connector face views, connector pinout diagrams, component locators, wiring schematics, and diagnostic flowcharts related to the code and the specific vehicle.
Check for battery voltage at the immobilizer warning lamp circuit using the appropriate wiring diagram and your DVOM. If not, check the system fuses and relays and replace faulty parts as needed. If voltage is found at the immobilizer warning lamp, suspect a faulty immobilizer warning lamp bulb.
If the immobilizer warning lamp bulb is functioning correctly and the P0648 continues to reset, use the DVOM to test the controller power fuses and relays. Replace blown fuses as needed. Fuses should be tested under load.
If all fuses and relays appear to be functioning correctly, a visual inspection of the wiring and harnesses related to the controller is necessary. You will also want to check the chassis and engine ground connections. Use your vehicle information source to obtain ground locations for the related circuits.
Visually inspect the system controllers for signs of water, heat, or collision damage. Any damaged controller, especially by water, should be considered faulty.
If the controller power and ground circuits are intact, suspect a faulty controller or a controller programming error. Replacing the controller will require reprogramming. In some cases, you can purchase pre-programmed controllers from aftermarket sources. Other vehicles/controllers will require onboard reprogramming that can only be performed by a dealer or other qualified source.
If the immobilizer lamp does not illuminate during Key On Engine Off (KOEO), suspect a faulty immobilizer warning lamp bulb
Test the controller ground integrity by connecting the DVOM’s negative test lead to ground and the positive test lead to battery voltage