Diesel Trouble Codes

P0201 — Injector Circuit/Open - Cylinder 1 (LLY / LBZ / LMM Duramax)

P0201 is an electrical fault detected by the ECM in the fuel injector circuit for cylinder 1 on LLY/LBZ/LMM Duramax 2004.5–2010. The code is generic SAE J2012…

Updated September 2, 2026

What it means

The ECM has detected an electrical fault in the fuel injector circuit for cylinder number one. Generic definition: The engine control module has detected an electrical fault in the fuel injector circuit for cylinder number one. Platform: LLY / LBZ / LMM Duramax.1

Most likely causes

  1. Open or high resistance in injector 1 harness/connector to the external injector — LLY/LBZ/LMM use Bosch common-rail injectors mounted externally (not under valve covers). Inspect external injector 1 connector, terminals, and wiring for corrosion, pin back-out, chafing, or moisture ingress along the engine harness. ECM monitors injector circuit continuity; an open/high resistance sets P0201.1
  2. Failed injector 1 solenoid/coil or internal open — Electrical fault in the injector driver circuit can be an internal open in the injector solenoid. Compare injector 1 electrical signature to other cylinders using a scan tool bi-directional test or scope the injector command vs. actual current. Do not disassemble high-pressure fuel lines.1
  3. ECM injector driver fault for cylinder 1 — ECM internal driver or related power/ground supply issue affecting cylinder 1 injector control. Verify ECM power/ground circuits and check for other injector codes. Isolated P0201 points to cylinder 1 circuit; multiple P02xx codes suggest ECM or harness power/ground.1
  4. Chafed/broken wiring in engine harness near valve cover or injector rail — External injector wiring runs along the valve cover/rail area and is exposed to heat/vibration. Inspect harness routing for abrasion, melted insulation, or connector fretting at injector 1.1

How to diagnose

  1. Verify code and freeze frame; confirm P0201 is current and note engine conditions at set.
  2. Visually inspect external injector 1 connector and harness for corrosion, damage, or loose terminals. Compare to other injectors.
  3. Check ECM connector and related grounds/power feeds for corrosion or looseness.
  4. Use scan tool to view injector circuit status and perform injector electrical tests if supported; compare cylinder 1 to others.
  5. Inspect harness routing for chafing near valve cover/injector rail and along the engine bay.
  6. If available, scope injector command signal at ECM and at injector connector to isolate wiring vs. injector vs. ECM.
  7. Clear codes and re-evaluate after repairs; monitor for pending codes and contribution/balance data.

Parts and tools you may need

Rough cost and difficulty

Diagnostic labor varies by shop. Parts costs vary by source and condition. Electrical diagnosis typically requires labor for inspection, cleaning, or harness repair; injector replacement involves high-pressure fuel system service and should be performed by qualified technicians.

When to see a pro

Refer to a qualified diesel technician for high-pressure fuel system work, ECM diagnostics, or wiring repairs. Do not perform step-by-step repair of safety-critical high-pressure fuel components.

Sources

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