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 October 15, 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

Tools you’ll need

Rough cost and difficulty

Likely repairPartsShop laborWho usually does it
Wiring or connector repair$10–$1001–4 hrsDIY with tools and a manual
Engine wiring harness section$100–$5002–5 hrsShop
Fuel injector (each)$300–$5501.5–3 hrsShop
ECM/PCM replacement (programmed)$600–$2,0001–3 hrsShop

Typical US independent-shop figures; labor runs about $120–$180 per hour (dealers charge more). Confirm the diagnosis before buying parts.

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.

Check for recalls

Recalls are tied to your truck’s VIN, so check yours directly: enter the VIN at NHTSA’s recall lookup. Open safety recalls are repaired free at a dealer.

Sources

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

Repair videos: P0201 on the LLY-LMM Duramax

Third-party videos, not ours — picked for this engine. Confirm anything against the factory service information for your truck.

LLY Duramax injector control circuit misfire cyl 7 cyl 2 pigtail ice pick fix — Richie's Diesel Performance · 157K views

Duramax LLY Injector Fix - watch before replacing the injectors — Mogleybear · 115K views