OBD Guide
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C120B

Ignition Supply Voltage Low

C120B is an OBD-II diagnostic trouble code meaning: Ignition Supply Voltage Low. Common causes: low or faulty battery, generator malfunction. Estimated repair cost: $22–111.

Severity
⚠️ Medium
Can you drive?
Limited driving only, diagnose soon
Approx. repair cost
$22–111 (est.)

Symptoms

  • Misfires
  • Unstable engine operation
  • Difficulty starting the engine
  • Power reduction
  • Check Engine Light Is On

Causes

  • Low or faulty battery
  • Generator malfunction
  • Damaged wiring harness
  • Poor contacts in the ignition circuit
  • Faulty relays or fuses

How to Fix

  1. Check battery voltage and alternator charging
  2. Inspect the wiring harness for damage
  3. Check contacts and terminals for oxidation
  4. Replace faulty fuses or relays
  5. If necessary, replace ignition system components

Related codes

P0300P0301P0351P0622

FAQ

What does the C120B code mean?

C120B is an OBD-II diagnostic trouble code that indicates: Ignition Supply Voltage Low

What causes a C120B error code?

The most common causes of C120B include: Low or faulty battery; Generator malfunction; Damaged wiring harness; Poor contacts in the ignition circuit.

How do I fix a C120B diagnostic trouble code?

To fix C120B: Check battery voltage and alternator charging. Inspect the wiring harness for damage. Check contacts and terminals for oxidation. For a complete diagnosis, use an OBD-II scanner.

Is it safe to drive with C120B?

Limited driving only, diagnose soon

How much does it cost to fix C120B?

The estimated repair cost for C120B is $22–111. Actual cost depends on your vehicle, location, and labor rates.

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See also: Russian version · NationStat