P0261 on the 6.0L Power Stroke is a cylinder 1 injector circuit low fault. The 6.0L uses HEUI injectors that are fired electrically by the fuel injection control module (FICM), which sends high-voltage pulses through the valve cover harness to each injector solenoid. P0261 tells you the FICM saw the cylinder 1 injector control circuit reading low, meaning a short to ground, an open, or a solenoid that is not drawing current correctly on that specific cylinder.
Because P0261 names a single cylinder, it narrows the search compared with a general injector code. That is helpful, because the 6.0L routes injector power through connectors and a harness under the valve cover where oil and heat degrade wiring over time. The fault is usually electrical rather than a worn injector body, so tracing the circuit for cylinder 1 pays off before you condemn the injector itself.
What P0261 means
The FICM drives each injector solenoid with a high-voltage pulse and monitors the circuit. P0261 sets when the cylinder 1 control circuit reads low, indicating a short to ground, an open, or a solenoid that does not respond as expected. It is an electrical code that points at the wiring, the under-valve-cover connector, or the cylinder 1 injector solenoid rather than at fuel delivery inside the injector.
Common causes
- Damaged valve cover harness or corroded under-valve-cover connector on cylinder 1
- Injector wiring shorted to ground or chafed
- Failed cylinder 1 injector solenoid
- Low FICM operating voltage stressing the circuit
- Oil intrusion in the injector connector
Symptoms
- Misfire, rough idle, or a dead cylinder feel
- Reduced power and hesitation
- Hard starting, especially when hot
- Check engine light with P0261 stored
- Possible smoke from unburned fuel
How to diagnose it
Start by checking FICM operating voltage with a scan tool, since low FICM voltage can trigger injector circuit codes across cylinders. Perform an injector buzz test and note whether cylinder 1 responds; a click on that cylinder confirms the solenoid is firing, while silence points to the circuit or solenoid. Inspect the valve cover harness and the under-valve-cover connector for oil, corrosion, and cracked insulation. Measure the cylinder 1 solenoid resistance and check the wiring from the FICM for a short to ground or an open.
How to fix it
Repair chafed or shorted wiring and clean or replace a corroded under-valve-cover connector first, as these resolve many single-cylinder injector faults. Correct low FICM voltage by repairing power and ground circuits or replacing the FICM if its output is weak. If the wiring and FICM are good but the cylinder 1 solenoid fails testing, replace that injector. After the repair, clear the code, confirm cylinder 1 responds in a buzz test, and road test. For valve cover harnesses, connectors, FICMs, and injectors for your 6.0L, contact sales@coredieselparts.com.
Frequently asked questions
Does P0261 mean my cylinder 1 injector is bad?
Not necessarily. It is an electrical circuit code, so check the valve cover harness, the under-valve-cover connector, and FICM voltage before replacing the injector, since wiring is a frequent cause.
Can low FICM voltage set P0261?
Yes. The FICM boosts voltage to fire the injectors. When its output drops, individual injector circuits can behave abnormally and set cylinder-specific codes.
Will P0261 cause a misfire?
Usually yes. If cylinder 1 is not firing correctly, you feel a rough idle, reduced power, and possibly smoke until the circuit is repaired.
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