OBD Guide
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P121A

Cylinder Balance Test Injector Restricted

P121A is an OBD-II diagnostic trouble code meaning: Cylinder Balance Test Injector Restricted. Common causes: dirty or clogged nozzle, nozzle wear. 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
  • Vibrations at idle
  • Reduced engine power
  • Increased fuel consumption
  • Dips during acceleration

Causes

  • Dirty or clogged nozzle
  • Nozzle wear
  • Problems with the fuel filter
  • Low pressure in the fuel system
  • Injector electrical circuit malfunction

How to Fix

  1. Check the condition of the fuel filter
  2. Clean or replace the problematic injector
  3. Check the pressure in the fuel system
  4. Check the injector electrical circuit
  5. Balance the cylinders after repair

Related codes

P0200P0201P0202P0203

FAQ

What does the P121A code mean?

P121A is an OBD-II diagnostic trouble code that indicates: Cylinder Balance Test Injector Restricted

What causes a P121A error code?

The most common causes of P121A include: Dirty or clogged nozzle; Nozzle wear; Problems with the fuel filter; Low pressure in the fuel system.

How do I fix a P121A diagnostic trouble code?

To fix P121A: Check the condition of the fuel filter. Clean or replace the problematic injector. Check the pressure in the fuel system. For a complete diagnosis, use an OBD-II scanner.

Is it safe to drive with P121A?

Yes, but get it checked soon

How much does it cost to fix P121A?

The estimated repair cost for P121A is $17–89. Actual cost depends on your vehicle, location, and labor rates.

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See also: Russian version · NationStat