OBD Guide
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U121B

Hard Disk Drive Communication Error

U121B is an OBD-II diagnostic trouble code meaning: Hard Disk Drive Communication Error. Common causes: poor contact of the hard drive connector, mechanical damage to the hard drive. Estimated repair cost: $33–167.

Severity
⚠️ Medium
Can you drive?
Yes, but get it checked soon
Approx. repair cost
$33–167 (est.)

Symptoms

  • Multimedia system failure
  • No access to navigation
  • Saved audio files disappearing
  • Rebooting the system while running
  • Error message on display

Causes

  • Poor contact of the hard drive connector
  • Mechanical damage to the hard drive
  • Multimedia system controller malfunction
  • Damage to the disk file system
  • Incompatible software

How to Fix

  1. Check the physical connection of the hard drive
  2. Test the hard drive on other hardware
  3. Update system software
  4. Perform a file system restore
  5. Replace the hard drive if necessary

Related codes

U121AU121CU122B

FAQ

What does the U121B code mean?

U121B is an OBD-II diagnostic trouble code that indicates: Hard Disk Drive Communication Error

What causes a U121B error code?

The most common causes of U121B include: Poor contact of the hard drive connector; Mechanical damage to the hard drive; Multimedia system controller malfunction; Damage to the disk file system.

How do I fix a U121B diagnostic trouble code?

To fix U121B: Check the physical connection of the hard drive. Test the hard drive on other hardware. Update system software. For a complete diagnosis, use an OBD-II scanner.

Is it safe to drive with U121B?

Yes, but get it checked soon

How much does it cost to fix U121B?

The estimated repair cost for U121B is $33–167. Actual cost depends on your vehicle, location, and labor rates.

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See also: Russian version · NationStat