OBD Guide
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P121B

Cylinder Balance Test Injector Blocked

P121B is an OBD-II diagnostic trouble code meaning: Cylinder Balance Test Injector Blocked. Common causes: dirty or clogged nozzle, problems with the injector electrical circuit. Estimated repair cost: $17–89.

Severity
⚠️ Medium
Can you drive?
Yes, but get it checked soon
Approx. repair cost
$17–89 (est.)

Symptoms

  • Uneven engine operation
  • Increased vibrations
  • Power reduction
  • Increased fuel consumption
  • Check Engine Light Is On

Causes

  • Dirty or clogged nozzle
  • Problems with the injector electrical circuit
  • Malfunction of the engine control unit (ECU)
  • Mechanical damage to the injector
  • Low fuel pressure

How to Fix

  1. Check the condition of the injector for contamination
  2. Check the electrical circuit of the injector for opens and shorts
  3. Check the fuel pressure in the system
  4. Clean or replace the nozzle if necessary
  5. Check and, if necessary, replace the computer

Related codes

P121AP121CP121D

FAQ

What does the P121B code mean?

P121B is an OBD-II diagnostic trouble code that indicates: Cylinder Balance Test Injector Blocked

What causes a P121B error code?

The most common causes of P121B include: Dirty or clogged nozzle; Problems with the injector electrical circuit; Malfunction of the engine control unit (ECU); Mechanical damage to the injector.

How do I fix a P121B diagnostic trouble code?

To fix P121B: Check the condition of the injector for contamination. Check the electrical circuit of the injector for opens and shorts. Check the fuel pressure in the system. For a complete diagnosis, use an OBD-II scanner.

Is it safe to drive with P121B?

Yes, but get it checked soon

How much does it cost to fix P121B?

The estimated repair cost for P121B is $17–89. Actual cost depends on your vehicle, location, and labor rates.

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See also: Russian version · NationStat