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Engine-Codes – Generic – C120B

C120B Code - Ignition Supply Voltage Low

Quick Answer

The C120B code signifies that the ignition supply voltage in the vehicle is lower than the specified threshold. Common causes include Faulty wiring, Weak or failing battery, Failing alternator. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means
C120B indicates Ignition Supply Voltage Low.
Common causes
Common causes include Faulty wiring, Weak or failing battery, Failing alternator.
Severity
High - diagnose this code as soon as possible.
Can I drive?
Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
What is this?
Table of contents Created and updated by William Orellana on Sep 09, 2024
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Code C120B Description

The C120B code signifies that the ignition supply voltage in the vehicle is lower than the specified threshold. This can lead to a variety of issues that affect the performance and overall functionality of the vehicle. The ignition supply voltage is crucial for starting the engine, powering various electrical components, and ensuring the smooth operation of the vehicle's systems.

OBDII Code C120B - Ignition Supply Voltage Low
C120B Code - Ignition Supply Voltage Low

Common Causes of C120B

  1. Faulty wiring
  2. Weak or failing battery
  3. Failing alternator
  4. Malfunctioning ignition switch
  5. Corrosion or loose connections in the electrical system

Symptoms of C120B

  1. Difficulty starting the engine
  2. Rough idling or stalling
  3. Dimming lights or flickering gauges
  4. Intermittent power loss
  5. Complete engine failure

How to Fix C120B

  1. Perform a thorough inspection of the wiring and connections to identify any issues.
  2. Test the battery and alternator to determine if they are functioning properly.
  3. Replace any damaged wiring, connectors, or components.
  4. Repair or replace the faulty battery, alternator, or ignition switch as needed.
  5. Clear the diagnostic trouble codes and reset the system to ensure the issue is resolved.

Cost to Fix C120B

The cost of repairing the C120B code can vary depending on the specific cause of the low ignition supply voltage. On average, the repair costs can range from $100 to $500, including parts and labor. It is important to note that the actual cost may be higher or lower based on factors such as the location of the repair shop, the make and model of the vehicle, and the extent of the damage. Additionally, diagnostic time and labor rates at auto repair shops can impact the final cost, so it is advisable to obtain a detailed estimate before proceeding with the repairs.

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Code C120B Information for Specific Makes

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about C120B Code

1. What does the OBDII code C120B mean?

C120B indicates that the ignition supply voltage is below the required level for proper operation of the vehicle's systems, which can affect various components, especially those in the ABS or stability control system.

2. What are the common symptoms of the C120B code?

Symptoms may include the ABS or traction control warning light on, erratic ABS or stability control behavior, and difficulty starting the vehicle or intermittent electrical issues.

3. What causes the C120B code to appear?

Common causes include a weak or failing battery, loose or corroded battery terminals, a faulty alternator, damaged wiring, or issues with the ignition switch.

4. How serious is the C120B code?

While the vehicle may still be drivable, this code can affect critical safety systems like ABS and traction control. It should be addressed promptly to avoid further electrical issues or compromised safety.

5. Can a low battery trigger the C120B code?

Yes, a low or failing battery is a common cause of the C120B code because insufficient voltage can disrupt the operation of the ignition and other systems.

6. How can I fix the C120B code?

Start by checking the battery’s charge and condition, inspect and clean the battery terminals, verify the alternator’s output, and examine the wiring and connections for damage or corrosion.

7. Can I clear the C120B code without fixing the problem?

You can clear the code with an OBDII scanner, but if the underlying issue isn’t resolved, the code will likely return and could lead to further electrical or safety system problems.

8. How do I test the alternator if I have a C120B code?

Use a multimeter to check the alternator’s output voltage. It should typically read between 13.5 and 14.7 volts when the engine is running. Anything outside this range may indicate a faulty alternator.

9. Is a damaged ignition switch a potential cause of the C120B code?

Yes, a damaged or failing ignition switch can cause low voltage to critical systems, potentially triggering the C120B code.

10. Can driving with the C120B code damage my vehicle?

While it may not immediately harm the vehicle, prolonged driving with this issue can lead to further electrical problems or disable key safety systems like ABS, increasing the risk of an accident.

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