Fuel injector codes

How its codes differ

• A cylinder misfire code (P0301 to P0306) that stays on one cylinder after the coil and plug have been swapped points toward that cylinder's injector or its compression.
• A lean code on one bank only (P0171 or P0174 alone on a V-engine) can come from a low-flowing injector on that side; both banks lean is less likely to be injectors.
• A rich code (P0172) can come from an injector that leaks or does not close fully.
• Converter codes (P0420, P0430) can follow a leaking injector, because the extra fuel overheats and coats the converter.
• P0175 (bank 2 rich) can come from a leaking or stuck-open injector on that bank.

Codes

• P0301

  Misfire detected in cylinder 1

  Severity: Inspect soon

• P0302

  Misfire detected in cylinder 2

  Severity: Inspect soon

• P0303

  Misfire detected in cylinder 3

  Severity: Inspect soon

• P0304

  Misfire detected in cylinder 4

  Severity: Inspect soon

• P0305

  Misfire detected in cylinder 5

  Severity: Inspect soon

• P0306

  Misfire detected in cylinder 6

  Severity: Inspect soon

• P0300

  Random or multiple-cylinder misfire detected

  Severity: Inspect soon

• P0171

  Engine computer has reached its limit adding fuel on bank 1: the mixture is lean

  Severity: Monitor

• P0174

  Engine computer has reached its limit adding fuel on bank 2: the mixture is lean

  Severity: Monitor

• P0172

  Engine computer has reached its limit removing fuel on bank 1: the mixture is rich

  Severity: Monitor

• P0420

  Catalytic converter efficiency below the computer's limit (Bank 1)

  Severity: Monitor

• P0430

  Catalytic converter efficiency below the computer's limit (Bank 2)

  Severity: Monitor

• P0175

  Engine computer has reached its limit removing fuel on bank 2: the mixture is rich

  Severity: Monitor

Signs it's failing

• Misfire on one cylinder
• Rough or unstable idle
• Hard starting
• Loss of power
• Higher fuel use

How to test it

1. Use misfire counters and the coil and plug swap test first; if the misfire stays on one cylinder, the injector becomes a suspect. (Low risk)

2. Injector resistance, pulse and balance tests, and fuel pressure checks, need service information and equipment; have a shop do them. (Best left to a shop)

   Warning: The fuel system stays under pressure after the engine stops, and leaking fuel can cause injury or fire. Pressure relief and fuel line work belong in a shop.

After the repair

• Check for fuel leaks at the injector seals before driving.
• Clear codes and check misfire counters and fuel trims after a drive.
• Clear codes only after the repair, then drive normally over several days with both city and highway driving so the readiness monitors can complete; clearing codes or disconnecting the battery resets them to not ready, which fails an emissions test.