P0261 — Cylinder 1 Injector Circuit Low — 6.0 Power Stroke

Diagnostic reference for P0261 on 6.0L Power Stroke (2003.5–2007).

Updated October 15, 2026

What it means

Generic definition: The engine control module has detected low electrical current or voltage in the cylinder 1 injector circuit. On the 6.0L injector circuits are driven and monitored by the 48 V FICM, so this code is usually stored in the FICM and flagged in the PCM by P1316.¹²

Most likely causes

1. FICM output voltage low / FICM performance fault — FICM supplies ~48 V to fire HEUI injectors. Low FICM voltage causes injector-circuit faults and is flagged by P0611 and P1316. Check FICM voltage key-on and cranking; inspect power/ground feeds to the FICM.¹²³
2. Under-valve-cover harness or connector fault at cylinder 1 — Per-cylinder circuit faults P0261…P0284 are detected by the FICM. The under-valve-cover harness and connector for cylinder 1 can chafe, oil-contaminate, or lose terminal tension, producing a low-current reading on that injector circuit.¹²
3. Cylinder 1 injector coil/open or high resistance — Each HEUI injector has two coils (open/close spool). An open or high-resistance coil on cylinder 1 reduces current draw and sets a low-circuit code. Verify injector coil resistance per service spec and compare to other cylinders.¹

How to diagnose

1. Verify freeze-frame and confirm P0261 is present with or without P1316; read FICM codes to see if the FICM has stored a cylinder-1 circuit fault.
2. Check FICM supply voltage: measure FICM output ~48 V key-on and while cranking; inspect batteries, cables, and FICM grounds. Low voltage points to power/ground or FICM performance.
3. Inspect under-valve-cover harness and connector for cylinder 1 for oil intrusion, chafing, or terminal damage; check continuity and isolation of the injector control wires from the FICM connector to the valve-cover pass-through.
4. Measure cylinder 1 injector coil resistance and compare to other cylinders; look for open/high resistance indicating a coil fault.

Specs and test values

Common mistake to avoid

Condemning the FICM or injectors before checking the batteries. The FICM needs good battery voltage to hold its output; weak batteries or a poor charging system can drag it below spec and look like a module failure. Source: DieselHub — 6.0 Power Stroke FICM troubleshooting.

Parts and tools you may need

• Digital multimeter
• Scan tool capable of reading FICM codes
• Basic hand tools for valve-cover access

Tools you’ll need

• digital multimeter — Measures FICM 48 V output, battery voltage, and injector coil resistance to isolate low voltage or open coil faults.
• OBD-II scan tool — Reads P0261 and P1316 plus FICM codes and freeze-frame to confirm the cylinder-1 injector circuit fault.
• fuel injection control module tester — Verifies FICM 48 V supply under load and injector driver performance for cylinder 1.
• inspection mirror and flashlight — Allows visual inspection of under-valve-cover harness and connector for oil intrusion or terminal damage.

Rough cost and difficulty

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 diagnosis points to internal injector failure or FICM replacement, have a qualified diesel technician perform the work. Do not attempt high-pressure oil or injector removal 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