Error Code P0561 is defined as System Voltage Unstable, meaning there’s an abnormal voltage reading coming from the battery, charging system, or the starting system of the vehicle. A dead alternator or battery often cause this issue.

This code is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system, particularly those made in 1996 up to present. It is particularly common among Dodge, Ford, GM, Hyundai, Jeep, Kia, and Mercedes vehicles. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model to another.

For a certain extent, the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) controls the charging system of a vehicle, by controlling the power or ground circuit to the voltage regulator inside the alternator.

Even when the vehicle is turned off, the battery still sends electricity to the PCM, this power is then used by the latter to store code histories, fuel trim values, and various data. If the battery voltage drops lower that specified level, the PCM will assume that there’s a problem with the power supply circuit, and will assume that there’s a problem and store this code.

Common Symptoms

As with other error codes, this code activates the Check Engine light and registers the code to the vehicle’s memory system. Other common symptoms include:

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  • Slow starting
  • Engine stalling at idle
  • Increase in fuel consumption
  • Low battery power also results to interior lights and other electrical components to not function properly

Possible Causes

The most common cause for this code is a dead or weakened battery, but it could also be a result of other issues, such as:

  • Defective alternator
  • Loose alternator belt
  • Defective starter
  • Opened or shortened voltage circuit
  • Opened or shortened battery cables
  • Defective voltage regulator
  • Corrosion in the battery terminals
  • Other malfunctioning system causing battery drain
  • Defective PCM (rare)

How to Check

As with most codes, it is best to start your diagnosis of this error code with the use of a TSB (Technical Service Bulletin) for your particular vehicle. Vehicle manufacturers release troubleshooting and repairs for known issues.

The most common cause for this problem is low battery voltage, disconnected battery, or faulty alternator which causes a problem in the charging system. In this case, it’s important to check the alternator belt as well.

Check the Charging System

The first step, check the charging system. Start the engine, and then load the electrical system by turning the headlights on and blower fan to high speed. Using a DVOM (digital volt-ohmmeter) check the battery’s voltage. It should be between 13.2V and 14.7V. If the voltage is lower than 12V or more than 15.5V, then you need to inspect the charging system, with emphasis on the alternator.

If unsure, have your battery, starting and charging system tested at an auto repair shop or a local parts store. You can also ask for a printout of the result. They can perform this service for a small charge, some even for free,

If the voltage is correct, then clear the diagnostic trouble codes from the memory using your scan tool to see if the code returns. If it does NOT return, then this code is either intermittent or is a history/memory code, and no further diagnosis may be required.

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If the code DOES return, then locate the PCM and check its connectors and wirings. Look for signs of damage, such as bare wires, burn spots, melted plastic, rubbing, scraping, etc. Pull the connectors apart and check the metal parts of the terminals within the connectors, and look for signs of burnt or corrosion (green tint). If the terminal needs cleaning, clean it using electrical contact cleaner and a plastic bristle brush. Let it dry and apply electrical grease where the terminals contact.

Then, clear the codes using the scan tool, and if it comes back. If it does NOT, then you have problems on your connection.

If the code comes back again, then you have to check the voltage to the PCM. Disconnect the negative connection at the battery. Then, disconnect the harness that goes to the PCM. Reconnect the battery cable and then turn the ignition switch on. Using the DVOM, test the PCM ignition feed circuit (red lead to the PCM ignition feed circuit, black lead to good ground). If there is less battery voltage on this circuit, then repair the wirings in the PCM connected to the ignition switch.

If it’s ok, then check to make sure you have a good ground at the PCM. Connect a test light on 12V battery positive (red terminal) and touch the other end of the test light to the ground circuit that goes to the PCM ignition feed circuit ground. If the light doesn’t light up, then the problem is the circuit. If it does light up, wiggle the harness that goes to the PCM to see if the light flickers. If it does flicker, then you have an intermittent connection problem.

How to Fix

Common repairs for this code include:

  • Replacement of the alternator
  • Replacement of the battery
  • Cable, connector, or wiring repair

For some vehicles with issues in the PCM, or in the additional charging and starting system failures, they may require more complex repairs or full replacements of defective components.

If after doing all tests you’re still getting the error code, then that means you have a failed PCM. In which case, you need the assistance of a professional technician to reprogram the PCM or calibrate the vehicle for it to be installed correctly.

Though this code is not a serious problem for the performance of the vehicle, it can affect other important systems, such as the security and locking system, audio, phone, navigation, in-vehicle entertainment systems, power seating systems, and climate control systems.