Diesel Trouble Codes

P0204 — Injector Circuit/Open Cylinder 4 (5.9 Cummins Common Rail)

Diagnostic reference for P0204 on 5.9L Cummins Common Rail 2003-2007. Covers what the code means, how to diagnose the electrical fault for cylinder 4 injector…

Updated September 2, 2026

What it means

The engine control module has detected an electrical fault in the fuel injector circuit for cylinder number four. On the 5.9L Cummins Common Rail 2003-2007 ISB, injectors are Bosch common-rail solenoid type and electrical faults show as P0201-P0206; contribution/balance issues use the P0263-family.12

Most likely causes

  1. Open or high-resistance in injector 4 harness/connectors — Inspect the injector 4 connector and engine harness for corrosion, backed-out pins, chafing, or oil intrusion at the valve cover pass-through. Check continuity from ECM to injector 4 and look for intermittent opens that set P0204.12
  2. Failed injector 4 solenoid/coil — A Bosch common-rail solenoid injector can develop an open coil. Compare injector 4 resistance to the other five injectors; a marked deviation suggests a failed injector solenoid.12
  3. ECM driver fault for cylinder 4 — If wiring and injector test good, the ECM internal driver for cylinder 4 may be faulty. Verify power/ground and harness integrity before condemning the ECM.1
  4. Valve cover gasket/oil intrusion affecting injector connector — Oil migration into the injector connector can cause poor contact and intermittent P0204. Inspect the valve cover area and connector seals for oil contamination.12

How to diagnose

  1. Verify code and freeze frame; confirm P0204 is present and not a phantom code from recent work.
  2. Visually inspect injector 4 connector, wiring, and valve cover pass-through for damage, corrosion, or oil intrusion.
  3. Measure injector 4 solenoid resistance and compare to cylinders 1,2,3,5,6; note any out-of-range reading.
  4. Perform a pin-to-pin continuity and isolation check from ECM harness connector to injector 4 connector; wiggle-test harness while monitoring.
  5. Check ECM power, ground, and reference voltages; confirm no other P020x codes are present.
  6. If wiring and injector pass tests, evaluate ECM driver for cylinder 4 with appropriate scan tool bi-directional tests or substitution logic.

Parts and tools you may need

Rough cost and difficulty

Parts and labor vary by region and shop. Electrical diagnosis typically requires labor for harness testing; injector replacement cost depends on part source and whether programming/bleeding is needed. Obtain quotes before proceeding.

When to see a pro

If wiring tests are inconclusive, intermittent faults persist, or ECM driver suspicion remains, have a qualified diesel technician perform pinpoint electrical tests and ECM evaluation. Do not attempt high-pressure fuel system disassembly. If the vehicle exhibits misfire, rough idle, or loss of power, avoid extended driving and seek prompt diagnosis.

Sources

  1. Curated DTC seed — 5.9 Cummins Common Rail (curated) ↩︎ ↩︎ ↩︎ ↩︎ ↩︎

  2. Curated DTC seed — 5.9 Cummins Common Rail (curated) ↩︎ ↩︎ ↩︎ ↩︎