P0205 — Injector Circuit/Open - Cylinder 5 — LB7 Duramax
Diagnostic guide for P0205 on LB7 Duramax (2001–2004).
What it means
The ECM has detected an electrical fault in the cylinder 5 injector circuit.1
Most likely causes
- Injector harness or connector fault under the valve cover on cylinder 5 — The LB7 injectors sit under the valve covers and are a well-known weak point; inspect the injector harness and connector under the valve cover for chafing, oil intrusion, or pin damage before condemning the injector.1
- Faulty cylinder 5 injector — On the LB7 the injectors sit under the valve covers and are a well-known weak point; check the injector harness and connector under the valve cover, then the injector.1
How to diagnose
- Verify code P0205 is present and check for accompanying misfire codes P0300/P0305.
- Inspect the under-valve-cover injector harness and connector for cylinder 5 for oil contamination, chafing, or damaged pins.
- Check ECM injector driver circuit continuity and isolation for cylinder 5.
- Assess injector electrical response for cylinder 5 using a scan tool bi-directional test or scope, comparing to other cylinders.
- Review fuel in oil, balance rates, and rough running symptoms consistent with LB7 injector weakness.
- Clear codes, road test, and confirm P0205 does not return.
Specs and test values
| Check | Normal reading | When to measure | Source |
|---|---|---|---|
| Injector balance rates | Healthy engines sit near ±2 mm³; values near ±4 mm³ or one cylinder far from the rest need a closer look | Hot idle in Park, A/C off | BD Diesel |
Common mistake to avoid
Buying injectors on balance rates alone. Compression, rail pressure and the pressure regulator all move balance rates; confirm a suspect injector with a return-flow test before replacing it. Source: BD Diesel — LB7 injectors: balance rates and return tests.
Parts and tools you may need
- Digital multimeter
- Scan tool with live data and bi-directional control
- Inspection light
- Basic hand tools for valve cover access
Tools you’ll need
- OBD-II scan tool — Reads P0205 and related misfire codes and runs bi-directional injector tests to compare cylinder 5 response.
- digital multimeter — Checks continuity and isolation of the cylinder 5 injector driver circuit and harness pins under the valve cover.
- oscilloscope — Captures injector electrical response waveform for cylinder 5 to identify driver or injector faults versus other cylinders.
- inspection mirror — Allows visual inspection of the under-valve-cover injector harness and connector for oil contamination and pin damage.
Rough cost and difficulty
| Likely repair | Parts | Shop labor | Who usually does it |
|---|---|---|---|
| Injector wiring harness / under-valve-cover harness | $50–$300 | 2–5 hrs | Shop |
| Fuel injector (each) | $250–$450 | 2–4 hrs | Shop |
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
If high-pressure fuel system work is required, seek a qualified diesel technician. Do not attempt high-pressure fuel injection system service without proper training and safety equipment.
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
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