Guide To P0648 OBD Error Code Solutions

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Diagnostic Trouble Code P0648 is technically described as Immobilizer Lamp Control Circuit. The Powertrain Control Module (PCM) monitors the Immobilizer Lamp Control Circuit. The PCM sets the OBDII code when the Immobilizer Lamp Control Circuit is not to factory specifications. In the event of an immobilizer lamp control circuit fault, a trouble code will be stored and a service engine soon lamp will be illuminated.

P0648 code means an abnormal reading in the immobilizer lamp control circuit has been detected due to a defective bulb, circuit, or faulty wiring. The immobilizer lamp is contained in the instrument panel. Its primary function is to warn the driver that the immobilizer key has malfunctioned or is not recognized (when it is illuminated). Each time the ignition is turned on and the PCM is energized, multiple controller self-tests are performed. Aside from running internal controller self-test, the CAN (controller area network) carries serial data from each module to make sure the onboard controllers are interfacing properly.

If a problem is detected in monitoring the immobilizer lamp control circuit, a code P0648 will be stored and a malfunction indicator lamp (MIL) may be illuminated.

What causes this problem with the Immobilizer Lamp Control Circuit?

• Open or shorted immobilizer lamp harness
• Poor electrical connection in immobilizer lamp circuit
• Defective immobilizer lamp
• Loose or broken control module ground strap or ground wire
• Faulty CAN bus
• Faulty PCM

1. Immobilizer lamp bulb - A defective immobilizer lamp bulb or circuit is usually the culprit behind a stored P0648 trouble code and it should be replaced immediately to avoid this trouble code.
2. Connectors - Connectors are one of the smallest parts which adjoins Immobilizer lamp circuit to different hoses, if they are loose or broken then it may cause damage to the related parts. Inspect the related connector carefully as it should not be loose, broken or corroded. If you discover it defective or damaged, replace it in no time.
3. PCM - A powertrain control module, abbreviated PCM, is an automotive component, a control unit, used on motor vehicles. It is generally a combined control unit, consisting of the engine control unit (ECU) and the transmission control unit (TCU). If it is faulty can lead to various trouble codes. Always repair or replace the faulty or failed PCM as soon as possible.

Most common symptom of this trouble code is illumination or flashing of the immobilizer lamp in addition to an illuminated Check Engine Light. Apart from these the other symptoms may include:

• Non-functional Immobilizer lamp
• Problematic start or no start
• Other stored codes

Note: If this code is stored, and a service engine soon lamp has not yet been illuminated, the code may be shown as pending.

Trouble Code P0648 might not create any drivability issues but can cause miscommunication between various control modules thus it should be fixed as soon as possible. Common repairs for this code include:

• Replacement of faulty components, connectors, and wirings.
• Replacement of defective CAN bus harness or the whole harness.
• Repair or replacement of straps, wires, and ground cables that are not properly connected.
• Replacement of faulty control modules (including PCM).
• Replacement or reprogramming of PCM.

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To avoid any mistakes while diagnosing this code, it is always recommended to have your vehicle diagnosed with the help of qualified technician. A diagnostic scanner, a digital volt/ohmmeter (DVOM), and a source of reliable vehicle information will be required to diagnose a code P0648. Steps to diagnose this code are as follows:

• Connect the scanner to the vehicle diagnostic port and retrieving all stored codes and freeze frame data.
• Clear the codes and 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 more difficult to diagnose.
• If the code is reset, continue with your diagnosis.
• Check to see if there is battery voltage on the speed control warning lamp circuit by using the appropriate wiring diagram and your DVOM.
• Replace blown fuses as required. Fuses should be tested with the circuit loaded.
• Visually inspect controller related wiring and harnesses is in order.
• Visually inspect system controllers for signs of water, heat, or collision damage.
• If controller power and ground circuits are intact, suspect a defective controller or a controller programming error.

Common Mistakes When Diagnosing the P0648 Code

Most common mistakes in addressing this code is treating any codes stored in reaction to the communication failure between the immobilizer lamp circuit and the PCM (or other control modules). This only treats the symptom and not the problem, causing the trouble code to return.

P0649 - Speed Control Lamp Control Circuit