Fault code P2505 – ECM/PCM power input signal malfunction

Fault code P2505 is called “ECM/PCM Power Input Signal 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 P2505

This diagnostic trouble code (DTC) is a generic code. Error P2505 is considered a generic code because it applies to all makes and models of vehicles. Although the specific repair steps may vary slightly depending on the model.

Fault code P2505 – ECM/PCM power input signal malfunction

OBD-II fault code P2505 is set when the transmission control module detects a power input fault. This occurs when the PCM power input goes outside of the factory specifications. Simply put, the power signal is out of the high or low limits set by the manufacturer.

The PCM requires a stable voltage to operate effectively, so manufacturers do their best to ensure that a stable current is always supplied to the control module. However, real-world operating conditions and adverse environmental factors make their own adjustments.

Extreme temperatures, vibration and humidity, create high voltages and stress on wiring, connectors and electrical components. These consist of thousands of connections that make up a vehicle’s electrical system.

Over time, impedance or signal continuity problems can occur in a vehicle’s electrical system. This is due to partial or complete loss of contact, corrosion in the wiring, or in the connectors.

Thus, when there are problems with a faulty input signal in the circuits that supply power to the PCM, there can be unpredictable results or symptoms. In some cases, the control module may deactivate itself as a protective measure.

In other cases, the only indication may be an illuminated signal lamp and a stored fault code. As long as the supply voltage fault does not damage the PCM to the point where the vehicle cannot move.

Symptoms of vehicle malfunctions

The main signal that an error P2505 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 light up (the code will be stored as a fault).
  2. Other related trouble codes may also be present.
  3. Floating revolutions, as well as attempts to stall at idle.
  4. The engine will either stall or start poorly.
  5. Sometimes there may be no symptoms despite a stored fault code.

Diagnostic fault code P2505 is considered serious, as the vehicle may experience handling and performance problems. For this reason, this error should be corrected as soon as possible.

Factors that can cause this error code

The error code P2505 can mean that one or more of the following problems have occurred:

  • Battery failure.
  • Poor contact between battery terminals and battery terminals due to corrosion or acid buildup.
  • Damaged, corroded wiring or connectors.
  • Blown fuse.
  • Alternator is not charging the battery normally.
  • Defective PCM relay.
  • Transmission control module is defective.

How to fix or reset OBD-2 code P2505

Some suggested steps for troubleshooting and fix the error code P2505:

  1. Inspect the PCM wiring for damage, abrasions, breaks, and shorts. If the wiring is damaged, repair or replace it.
  2. Inspect the battery cables for loose connections, broken terminals, and corrosion. Repair or replace the battery cables if necessary.
  3. Remove all diagnostic trouble codes from the PCM and test drive to see if diagnostic trouble code P2505 returns.
  4. If the code returns, check the PCM relay to make sure it is working properly.
  5. Inspect and check the fuse and fusible link.
  6. Check the wiring diagram of the relay and fuse system.
  7. Test the battery and charging system for proper operation. If necessary, repair or replace the battery or charging system components.
  8. Clear the fault codes again and perform a test drive.
  9. Insert the key in the ignition switch and turn it to the on position. If the Check Engine light does not come on, but the code in memory appears again, the relay may be faulty.
  10. If the relay is good, it may be necessary to replace and reprogram the PCM.

Diagnose and repair of problems

To rule out all possibilities for error P2505, visually inspect the wiring and check the battery voltage. Also check the battery terminals and cables for loose connections.

Ensure that the system voltage is as specified in the manual. The charging system is fully functional and the battery is in good condition, begin the diagnostic procedure. Check the ground connections between the battery and the engine and between the battery and the body for corrosion or poor contact.

Now find the starting point of the PCM power circuit. This is usually the ignition switch, so use a digital multimeter to check the voltage at this wire or terminal. Compare the reading with the value in the manual, and repair if necessary, if an abnormality is found.

If the code remains, but the power supply to and from the ignition switch is within the specified range. Note and test the power supply to the fuse box and then to the PCM connector. If abnormalities are found, make the necessary repairs. To ensure that all electrical parameters are in accordance with the manufacturer’s specifications.

The steps described above will help clear the P2505 error, but in some cases where the cause is not obvious, intermittent faults may be present. Also, if the PCM is already damaged it may require repair by a specialized repair shop.

On which vehicles does this problem occur most frequently

Fault code P2505 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • Ford
  • Mercedes-Benz (W204, W211)
  • Volvo

Fault code P2505 can sometimes be found with other errors. The most common are the following: P2506, P2507, P2508, P2509.


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