Diesel Trouble Codes

P0202 — Injector Circuit Malfunction Cylinder 2 (LLY / LBZ / LMM Duramax)

Diagnostic reference for LLY/LBZ/LMM Duramax 2004.5–2010. P0202 indicates the ECM has detected an electrical fault in the fuel injector circuit for cylinder 2.

Updated September 2, 2026

What it means

The engine control module has detected an electrical fault in the fuel injector circuit for cylinder number two. On LLY/LBZ/LMM Duramax, injectors are Bosch common-rail units mounted externally (not under valve covers) and the platform uses CP3 common rail with pump-mounted fuel pressure regulator.1

Most likely causes

  1. Open or high resistance in injector 2 harness/connector — External injector wiring and connector for cylinder 2 can develop opens, corrosion, or terminal fretting leading to circuit malfunction detection.1
  2. Short to ground or short to voltage in injector 2 circuit — Chafed harness or damaged insulation can cause a short that the ECM flags as a circuit malfunction.1
  3. Faulty injector 2 solenoid/electrical coil — Internal electrical failure of the injector solenoid produces an out-of-range circuit signature.1
  4. ECM driver fault for injector 2 — Internal ECM injector driver issue can set a circuit code for a specific cylinder.1

How to diagnose

  1. Verify code P0202 is present and check for accompanying misfire codes P0300/P0302; platform-specific misfire contributors include fuel-rail pressure control/CP3/regulator/injector balance.
  2. Inspect external injector 2 connector and harness for damage, corrosion, oil intrusion, and proper seating; injectors are externally mounted on LLY/LBZ/LMM.
  3. Perform pin-to-pin continuity and isolation tests of injector 2 circuit from ECM connector to injector connector; compare resistance to other cylinders.
  4. Measure injector 2 solenoid resistance per service spec and compare to cylinders 1,3,4,5,6,7,8; significant deviation suggests injector electrical fault.
  5. Check ECM injector driver outputs with a lab scope during commanded injection; abnormal waveform indicates wiring or ECM issue.
  6. Clear codes, run engine and monitor for P0202 reset; if code returns with no wiring fault, suspect injector or ECM.
  7. Note platform facts: LLY/LBZ/LMM use CP3 common rail, pump-mounted fuel pressure regulator, VGT turbo, glow plugs + control module, EGR/DOC (+DPF on LMM only), no DEF/SCR.

Parts and tools you may need

Rough cost and difficulty

Parts and labor vary by region and shop. Electrical diagnosis is typically lower cost than injector replacement; confirm root cause before replacing components.

When to see a pro

If circuit tests pass but P0202 persists, or if injector replacement is considered, have a qualified diesel technician perform injector electrical testing and ECM verification. Do not attempt high-pressure fuel system service without proper training and safety equipment. High-pressure fuel lines are safety-critical; diagnosis only, no step-by-step repair instructions here. If misfire or performance issues continue, professional diagnosis is recommended.

Sources

  1. Curated DTC seed — LLY / LBZ / LMM Duramax (curated) ↩︎ ↩︎ ↩︎ ↩︎ ↩︎