Fuel and air

P01D1 — Cylinder 4 Injection Timing Over-Retarded

Severity: medium Drive with care, to a shop

What P01D1 means

The engine control module compares the actual start of fuel injection in cylinder 4 with the calculated target. P01D1 sets when injection happens later than the allowed limit, meaning timing is over-retarded. It usually points to the injector, its control circuit, or the signals the ECM uses to track crankshaft position.

Symptoms

  • Check Engine light on
  • Rough idle or engine vibration
  • Reduced power or hesitation under load
  • Surging or jerking while driving
  • Increased fuel consumption
  • Smoke during cranking (some diesel engines)
  • Higher exhaust emissions

Possible causes

  1. Cylinder 4 injection timing deviating beyond the ECM's allowed limit
  2. Faulty or worn cylinder 4 fuel injector
  3. Damaged wiring, corroded pins or a bad connector in the injector circuit
  4. Fuel supply problems such as low pressure or a clogged filter
  5. Incorrect crankshaft position sensor signal
  6. Intake air leak skewing the mixture
  7. Internal ECM fault (uncommon)

How to diagnose

  1. Scan for all codes and freeze-frame data; note any other injector or misfire codes
  2. Review fuel trims and mixture adaptation values
  3. Compare cylinder balance or injector correction values and see if cylinder 4 stands out
  4. Inspect the cylinder 4 injector connector and harness; test circuit resistance and check for shorts to ground
  5. Measure fuel pressure against specification
  6. Test the crankshaft position sensor and its wiring
  7. Check the intake and exhaust for leaks
  8. Swap the injector with a neighboring cylinder and see whether the fault follows it

Common fixes

  • Repair or replace the cylinder 4 injector
  • Repair the injector wiring and connectors
  • Replace the fuel filter and fix the cause of low fuel pressure
  • Replace the crankshaft sensor if its signal is bad
  • Seal any air leaks
  • Reprogram or replace the ECM only after confirming an internal fault

Questions and answers

What does P01D1 mean?

The ECM detected that fuel injection in cylinder 4 starts later than it should. The usual culprits are the injector, its wiring or the fuel supply.

Can I drive with P01D1?

Briefly and gently, for example to a repair shop. Prolonged driving risks misfires, lost power and overheating of the catalytic converter.

Should I replace the injector right away?

No. Check the wiring, connector, fuel pressure and crankshaft sensor first. Swapping the injector with another cylinder helps confirm whether it is the cause.

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.