Fuel and air

P01D9 — Cylinder 8 Fuel Injection Timing Over-Retarded

Severity: medium Drive with care, to a shop

What P01D9 means

The engine control module compares the actual start of fuel injection on cylinder 8 with the target and finds it happening later than it should. This applies to engines where injection timing is electronically controlled, most often diesels. The cause can be the injector itself, its control circuit, the fuel supply, or ECM software.

Symptoms

  • Check Engine light on
  • Reduced power and sluggish acceleration
  • Worse fuel economy
  • Rough idle or vibration
  • Misfire-like behavior on cylinder 8
  • Hard starting or occasional stalling

Possible causes

  1. Cylinder 8 injector deviation: wear, sticking or clogging
  2. Damaged wiring or connector in the injector control circuit
  3. Low fuel pressure or poor fuel quality
  4. Air leaks or intake/exhaust problems skewing the mixture
  5. ECM software fault or outdated calibration
  6. Faulty sensors used to determine injection timing
  7. Failed ECM (rare)

How to diagnose

  1. Scan all codes and freeze frame data, looking for other injector or fuel system codes
  2. Review fuel trims and mixture adaptation values in live data
  3. Compare cylinder balance or per-cylinder corrections and look at cylinder 8
  4. Inspect the cylinder 8 injector harness and connector, and test resistance and shorts to ground
  5. Measure fuel pressure and check the condition of the fuel filters
  6. Check the intake and exhaust for leaks
  7. Bench test the injector, or swap it with a neighbor and see if the fault follows
  8. Check for an ECM software update

Common fixes

  • Clean, repair or replace the cylinder 8 injector
  • Repair the injector wiring and connectors
  • Replace fuel filters and fix the cause of low pressure
  • Seal air leaks
  • Update or reflash the ECM and run injector adaptation

Questions and answers

What does P01D9 mean?

The ECM detected that fuel injection on cylinder 8 starts later than it should. The usual suspects are the injector, its wiring, fuel pressure or the ECM software.

Can I drive with P01D9?

Briefly, to get to a shop, if the engine runs smoothly. If it shakes, loses power or smokes, don't keep driving, to avoid engine and exhaust damage.

How do I fix P01D9?

Start with the cylinder 8 injector wiring and connector, fuel pressure and fuel trims. If those are fine, test or replace the injector and update the ECM if needed.

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.