Fault code P0649 – immobilizer lamp control circuit malfunction

Fault code P0649 is called “Immobilizer Lamp Control Circuit Malfunction” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P0649

OBD-II fault code P0649 is a generic fault code that is most commonly defined as “Speed Control Lamp Control Circuit Fault”. It is set when the PCM detects a malfunction in the speed control lamp control circuit (cruise-control).

Fault code P0649 – immobilizer lamp control circuit malfunction

The speed monitor lamp is located on the dashboard. Its main function is to alert the driver that the speed control system is activated.

The speed control system is also called cruise control.

The PCM always monitors the continuity of the speed monitor lamp control circuit each time the ignition is turned on. The speed control system uses input signals from the vehicle speed sensor (VSS).

It also uses data from the wheel speed sensors to automatically adjust the vehicle speed. This occurs after the cruise control system is activated by the driver.

Each time the ignition is turned on and power is applied to the PCM, several self-tests of the controller are performed. In addition to performing internal controller self-tests. The Controller Area Network (CAN) transmits serial data from each individual module to allow interaction of the on-board controllers.

If a problem is detected while monitoring the speed lamp control circuit. The code P0649 will be stored and the Malfunction Indicator Light (MIL) may illuminate.

Symptoms of vehicle malfunctions

The main signal that an error P0649 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

  1. The “Check engine” control lamp on the control panel will illuminate (the code will be stored as a fault).
  2. The illuminated safety system warning light (speed control lamp) may or may not work.
  3. The speed control system may not work.
  4. Other speed control related trouble codes may also be present.

Fault code P0649 should be considered serious, because if you have it, you most likely will not be able to activate the cruise control function.

Factors that can cause this error code

The error code P0649 can mean that one or more of the following problems have occurred:

  • Defective cruise control lamp.
  • Open or short circuit in speed indicator control circuit.
  • Damaged, burned, shorted, or corroded wiring in CAN bus line.
  • Sometimes faulty PCM module is the cause.

How to fix or reset OBD-2 code P0649

Some suggested steps for troubleshooting and fix the error code P0649:

  1. Read all data and stored error codes, using an OBD-II scanner.
  2. Clear the codes and check if fault code P0649 appears again.
  3. Test the speed control lamp and printed circuit board on the instrument panel.
  4. Inspect the wiring for damage.

Diagnose and repair of problems

Start the diagnosis of fault P0649 by connecting the scan tool to the vehicle’s diagnostic port and retrieving all stored codes and data. After all necessary information has been written, clear the codes and test drive the vehicle.

If the error returns after resetting the code and test drive, you must continue diagnostics. Check if there is battery voltage in the speed warning lamp circuit using an appropriate wiring diagram.

If there is no voltage, check the system fuses and relays and replace the defective parts if necessary. If voltage is detected in the speed warning lamp, it will indicate that it is faulty.

If the speed warning lamp operates normally and code P0649 remains active, use a multimeter to check the fuses and the controller power relay. Replace the blown fuses if necessary.

If all fuses and relays are working properly, a visual inspection of the controller wiring and harnesses should be performed. Chassis and motor grounding should also be checked.

If the controller power and ground circuits are intact, you probably have a faulty controller or programming error. In some cases, reprogrammed controllers are available on the aftermarket.

On which vehicles does this problem occur most frequently

Fault code P0649 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • Chevrolet
  • Chrysler
  • Dodge
  • Ford
  • Honda
  • Hyundai
  • Jeep

Fault code P0649 can sometimes be found with other errors. The most common are the following: P0513, P0648, P0650.

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