P0261 — Cylinder 1 Injector Circuit Low — 7.3 Power Stroke
P0261 on a 7.3L Power Stroke (1999–2003 Super Duty/Excursion) means the PCM/IDM has detected low electrical current or voltage in the cylinder 1 injector…
What it means
The engine control module has detected low electrical current or voltage in the injector circuit for cylinder 1. On this platform the injectors are HEUI, IDM-driven, with UVCH known as a failure point. Typical on 7.3L Power Stroke (1999-2003 Super Duty/Excursion) — HEUI, IDM-driven injectors, UVCH known failure point.1
Most likely causes
- Open or high-resistance in cylinder 1 injector circuit (UVCH connector/pigtail, injector solenoid terminals, or IDM output wiring). — The 7.3 uses HEUI injectors under the valve covers fed by UVCH; oil-soaked/chafed UVCH is a known failure point for injector and glow-plug circuit codes. Per-cylinder circuit faults are P0261/P0262 for cyl 1, etc., with IDM/output-circuit faults P1660/P1662/P1663.12
- Faulty cylinder 1 injector solenoid/electrical coil (low current draw). — PCM/IDM monitors injector circuit current; low current indicates an open or weak solenoid. This is a per-cylinder injector circuit fault on HEUI, IDM-driven injectors.12
- Injector Driver Module (IDM) output fault for cylinder 1 driver. — Injectors are driven by the IDM (driver-side fender). IDM/output-circuit faults are P1660, P1662, P1663. A failing IDM can present as a single-cylinder low-circuit code.1
- Corrosion/moisture in under-valve-cover harness or valve-cover pass-through connector for cylinder 1. — UVCH connectors and pigtails live under each valve cover and are known to fail from oil exposure and chafing, commonly setting injector circuit codes.1
- Poor PCM/IDM power/ground or wiring harness chafing affecting cylinder 1 injector control wire. — Electrical integrity of the IDM-to-UVCH path is required for proper injector current monitoring; intermittent opens cause low-circuit detection.1
How to diagnose
- Verify code and freeze-frame; confirm P0261 is present and not accompanied by ICP/IPR or IDM codes.
- Inspect IDM power/ground and main engine harness for chafing/corrosion; check IDM connector pins for oil/moisture.
- Perform injector circuit electrical tests at the IDM connector and UVCH pass-through for cylinder 1 (continuity, resistance, isolation to ground). Compare to other cylinders.
- Inspect under-valve-cover harness and injector solenoid terminals for oil saturation, burnt pins, or damaged pigtails; look for signs of arcing.
- Swap IDM output test with a known-good IDM if available, or monitor IDM driver command vs. actual current with a scan tool capable of injector buzz test.
- If circuit tests normal, evaluate cylinder 1 injector solenoid resistance and compare to spec and other cylinders.
- Clear codes, perform injector buzz test and cylinder contribution test to confirm fault follows cylinder 1.
Specs and test values
| Check | Normal reading | When to measure | Source |
|---|---|---|---|
| Fuel pressure | 1994–97: 40–70 psi. 1998–2003: never below 30 psi (Ford spec 30–80); 50–60 psi typical at idle | Key on engine off, cranking and idle | DieselHub |
| Battery and charging voltage | 12.6–12.7 V at rest when fully charged; about 13.5 V running | Engine off, then running with loads on | DieselHub |
Parts and tools you may need
- Digital multimeter
- Scan tool with Ford/HEUI injector buzz and cylinder contribution tests
- Injector breakout box / IDM harness test adapter
- Torx and socket set for valve cover removal
- Dielectric grease
- Replacement UVCH and injector pigtail kit
- Replacement IDM (if testing indicates driver fault)
- Replacement HEUI injector (if solenoid electrical fault confirmed)
Tools you’ll need
- OBD-II scan tool — Reads P0261, freeze-frame, and runs injector buzz/contribution tests to confirm the fault stays on cylinder 1.
- digital multimeter — Measures injector solenoid resistance and circuit continuity/isolation to ground for cylinder 1 UVCH/IDM wiring.
- inspection light — Reveals oil saturation, burnt pins, or damaged UVCH pigtails under the valve cover for cylinder 1.
Rough cost and difficulty
| Likely repair | Parts | Shop labor | Who usually does it |
|---|---|---|---|
| Wiring or connector repair | $10–$100 | 1–4 hrs | DIY with tools and a manual |
| Injector wiring harness / under-valve-cover harness | $50–$300 | 2–5 hrs | Shop |
| Fuel injector (each) | $150–$350 | 1.5–4 hrs | Shop |
| IDM (injector driver module), reman | $330–$600 | 1–2 hrs | DIY with tools and a manual |
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 the injector buzz test shows no response, or if multiple injector codes appear, have a qualified diesel technician evaluate the IDM, UVCH, and high-pressure oil system. Do not attempt high-pressure oil line 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
Repair videos: P0261 on the 7.3 Power Stroke
Third-party videos, not ours — picked for this engine. Confirm anything against the factory service information for your truck.
Spotted an error, or something missing? Tell us
Run a 7.3 Power Stroke? This goes straight to the editor — it is not published.