OBD Guide
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U12B1

Power Supply Voltage High

U12B1 is an OBD-II diagnostic trouble code meaning: Power Supply Voltage High. Common causes: faulty generator (overcharging), wiring problems (short to power supply). Estimated repair cost: $6–56.

Severity
⚠️ Medium
Can you drive?
Do not drive — repair immediately
Approx. repair cost
$6–56 (est.)

Symptoms

  • The Check Engine light comes on
  • Unstable engine operation
  • Electrical problems (such as headlights being too bright)
  • Error messages from various ECUs
  • Possible problems starting the engine

Causes

  • Faulty generator (overcharging)
  • Wiring problems (short to power supply)
  • Voltage regulator malfunction
  • Battery problems
  • ECU malfunction

How to Fix

  1. Check the battery and alternator voltage with a multimeter.
  2. Inspect wiring and connectors for damage or corrosion.
  3. Check the generator voltage regulator.
  4. Check the ECU for damage or corrosion.
  5. Replace faulty components.

Related codes

U1000U1100U1200

FAQ

What does the U12B1 code mean?

U12B1 is an OBD-II diagnostic trouble code that indicates: Power Supply Voltage High

What causes a U12B1 error code?

The most common causes of U12B1 include: Faulty generator (overcharging); Wiring problems (short to power supply); Voltage regulator malfunction; Battery problems.

How do I fix a U12B1 diagnostic trouble code?

To fix U12B1: Check the battery and alternator voltage with a multimeter.. Inspect wiring and connectors for damage or corrosion.. Check the generator voltage regulator.. For a complete diagnosis, use an OBD-II scanner.

Is it safe to drive with U12B1?

Do not drive — repair immediately

How much does it cost to fix U12B1?

The estimated repair cost for U12B1 is $6–56. Actual cost depends on your vehicle, location, and labor rates.

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See also: Russian version · NationStat