Fuel and air

P01D2 — Cylinder 4 Injection Timing Over-Advanced

Severity: medium Drive with care, to a shop

What P01D2 means

The engine control module compares when injection actually starts in cylinder 4 with the calculated target and finds it is earlier than allowed. The usual suspects are the injector, its control circuit, fuel pressure or a shaft position error. On diesels such as the Duramax, injection timing is constantly trimmed using learned values.

Symptoms

  • Check engine light on
  • Rough idle
  • Misfire in cylinder 4
  • Reduced power
  • Higher fuel consumption
  • Harsh, knocking combustion noise
  • Increased smoke or emissions

Possible causes

  1. Faulty or worn cylinder 4 injector
  2. Open circuit, corrosion or poor contact in the injector wiring or connector
  3. Incorrect sensor data used to calculate injection timing
  4. Low or unstable fuel pressure
  5. Worn timing chain or belt, shifted cam or crank phasing
  6. Intake air leak distorting the mixture
  7. ECM fault or corrupted learned values

How to diagnose

  1. Read all codes and freeze frame data, and look for related fuel pressure or shaft sensor codes
  2. Inspect the cylinder 4 injector harness and connector for damage, oil and corrosion
  3. Test injector resistance, control circuit, power and ground
  4. Compare fuel trims and cylinder balance with a scan tool to confirm cylinder 4 is the outlier
  5. Measure fuel pressure against the manufacturer spec
  6. Check the intake and exhaust for leaks
  7. Check timing marks and chain or belt stretch
  8. Bench test the injector or swap it with a neighbor to see whether the fault follows it

Common fixes

  • Clean, test or replace the cylinder 4 injector
  • Repair wiring and replace damaged connectors
  • Fix the cause of low fuel pressure
  • Replace the timing chain or belt and set timing correctly
  • Run the injector relearn procedure with an OEM-level scan tool after repairs

Questions and answers

What does P01D2 mean?

The ECM found that injection in cylinder 4 starts earlier than it should. The most common causes are the injector, its wiring or fuel pressure.

Can I drive with P01D2?

Only briefly and under light load to reach a shop. Over-advanced injection can overload the cylinder and may damage the engine.

Do injectors need to be relearned after repair?

Often yes. After replacing an injector or repairing the circuit, correction values usually need to be relearned with a scan tool, or the code may return.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.