P0261: Cylinder 1 Injector Circuit Low
Diagnostic Trouble Code (DTC) P0261 indicates that the Engine Control Module (ECM/PCM) has detected that the electrical voltage in the fuel injector control circuit for Cylinder 1 has fallen below calibrated operational thresholds, or that excessive current has passed directly to ground. In common rail systems, the injector is supplied with high voltage (80V to 200V) from the ECM boost converter, and the low side is switched to ground by a high-speed power MOSFET. DTC P0261 is stored when the low-side control line is shorted to vehicle chassis ground, an internal coil insulation breakdown shorts the actuator to the cylinder head, or the ECM's internal output driver detects an abnormally fast current rise.
🚗 Operational Safety, Typical Repair Costs & Diagnostic Verification
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🚦 Driving Safety & Operational Risk
Immediate mechanical assessment and tow requirementsCylinder 1 Injector Circuit Short to Ground - Risk of Blowing ECU Boost Capacitors
The control circuit for Cylinder 1 injector is shorted to chassis ground. In common-rail injection systems, a grounded high-voltage driver wire will trip ECU over-current protection and shut down the bank.
MECHANICAL HAZARDS & ENGINE RISK IF DRIVEN:Sustained short circuit can destroy the internal high-voltage step-up capacitor bank within the engine control unit. - 02
💰 Typical Workshop Repair Budget
Expected parts replacement and garage labor cost tiersMinor DIY / Filter Purge$45 - $95 (Pinpoint Wiring Harness Pinch Point & Solder Heat-Shrink Repair)Sensor cleaning, fuel filter renewal, fuse replacement, or harness contact cleaning.
Sensor / Valve Replacement$220 - $520 (Cylinder 1 Injector Replacement if Internal Coil Shorted to Body)Single component fix (e.g. pressure regulator valve, inlet metering unit, or reconditioned injector).
Major Overhaul / Pump & Injectors$750 - $1,800 (ECU Power Stage Driver Repair or Complete Main Engine Harness)High-pressure injection pump overhaul, new OEM injector set, or DPF assembly replacement.
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🧰 Initial Visual & Physical Verifications
5-minute zero-tool garage triage steps before calling a workshop11. Inspect Cylinder 1 injector harness where it routes across the metal valve cover edge or fuel rail bracket for chafing.22. Disconnect injector plug and measure resistance between each wire and battery negative (should be open circuit / OL).33. Measure injector terminal resistance against injector steel casing. Any reading below 500 k-ohms proves internal coil breakdown. - 04
🛡️ Diagnostic Verification & Mechanic Shield
Exact questions to ask your technician to prevent unnecessary parts replacement""Disconnect Cylinder 1 injector and check if the short-to-ground fault code changes to an open-circuit code; this proves whether fault is in injector or wiring.""
""Do not replace the ECU without performing a 250V insulation megger test on the engine wiring loom.""
""Verify engine ground straps between cylinder head and chassis are tight and clean with less than 0.2 ohms resistance.""
Technical Note: Read these technical questions to your mechanic before approving expensive parts replacements:
30-Second Workshop Triage
- Violent engine shaking, severe shudder, and continuous single-cylinder misfire under all operating conditions
- Significant loss of vehicle acceleration, sluggish throttle response, and inability to maintain highway cruising speeds
- Illuminated Check Engine Light (MIL) accompanied by flashing glow plug warning light and ESP/traction warning
- Cylinder 1 injector low-side control wire pinched, chafed, or shorted to vehicle chassis ground against the cylinder head or valve cover
- Internal dielectric breakdown or winding short to ground inside the Cylinder 1 fuel injector electromagnetic solenoid or piezo stack
- Corroded, wet, or water-contaminated terminal pins inside the Cylinder 1 injector connector creating a conductive path to ground
Connect scan tool live telemetry: compare Target Fuel Rail Pressure vs Actual Rail Pressure and log metering valve command PWM duty cycle during idle and road load.
Expensive Diagnostic Pitfall & Technical Reality
P0261 means Cylinder 1 common rail fuel injector has failed internally and must be replaced immediately with full coding ($450 - $900).
P0261 indicates that the ECM's injector driver circuit detected that the Cylinder 1 high-side or low-side signal wire is shorted to ground or has an abnormally low voltage during actuation. In over 80% of verified cases, the injector solenoid coil itself is in perfect working order. The failure is driven by the engine wiring harness chafing through its protective sleeve and shorting to the cylinder head aluminum casing, engine oil contamination inside the valve cover harness connector, or terminal pins in the ECM plug being pushed back.
Unnecessarily spending $650 on a new injector vs finding the harness rub-through with a multimeter ($0) and insulating with $5 heatshrink, saving over $600.
Most Common Engines & Fuel Injection Platforms Affected
This fault code predominantly affects the following common rail diesel platforms. Cross-reference your specific engine family below for verified factory failure modes, key sub-assembly part numbers, and dedicated repair links:
BMW 2.0d / 3.0d (N47 / N57 / M57TU2)
Bosch CRI2.5 / CRI3.0 Common RailKnown Factory Failure Mode: Injector balance drift beyond +/- 4.0 mg/stroke, glow plug control unit (BERU) power lead failure, DPF backpressure accumulation.
13537805428, 0445116024, 12217801201Ford / PSA 1.6 TDCi / HDi (DV6ATED4 / DLD-416)
Bosch CRI2-16 Common Rail SystemKnown Factory Failure Mode: Injector copper washer blow-by (black death), injector cylinder circuit fretting corrosion, DPF pressure pipes heat cracking.
0445110239, 1980J7, 1618LPVolkswagen / Audi 2.0 TDI (EA189 / CFFB / CFGB)
Bosch EDC17 Common Rail SystemKnown Factory Failure Mode: Piezo stack degradation, injector harness terminal fretting, DPF differential pressure sensor silicone tube split.
03L130277, 0445110369, 076906051AMercedes-Benz 2.1 CDI (OM651 / OM646)
Delphi CRD2 / Bosch Common Rail InjectionKnown Factory Failure Mode: Delphi piezo to solenoid conversion wiring harness chafing, differential pressure sensor internal diaphragm drift.
A6510704987, A6510700587, A0061539528P0201-P0204 Injector Circuit Diagnosis Guide
Workshop troubleshooting guide for OBD-II codes P0201 to P0204 (Cylinder 1-4 Injector Circuit Malfunction). Resistance test specs, harness checks, and ECU driver stage.
Control Circuit & Actuator Logic
1. Dynamic In-Demand Fuel Metering
The Cylinder 1 common rail fuel injector circuit consists of a high-side supply line and a low-side control line. When firing, the ECM high-side driver gates an 80V-200V capacitor pulse, while the low-side driver pulls the return wire to ground, completing the circuit. The low-side circuit incorporates an internal diagnostic sense resistor. When the injector de-energizes, the collapsing magnetic field generates an inductive flyback voltage spike that is captured and evaluated by the ECM. If the low-side wire is pinched against the engine block, voltage remains pinned to 0V (ground), triggering P0261.
2. Closed-Loop PID Deviation Monitoring
The ECM executes circuit diagnostics both continuously during engine running and statically at Key-ON. If the voltage on the Cylinder 1 low-side driver line remains below 1.5 V during the un-energized rest state (where pull-up voltage is expected), or if the current-sense circuit detects immediate over-current upon initial gating, P0261 is set. To prevent the short circuit from draining the ECM's shared boost capacitor (which would shut down the entire cylinder bank), the ECM de-energizes the high-side supply to Cylinder 1.
3. Diagnostic Trap: Normally Open (NO) vs Normally Closed (NC) Valves
Short-to-Ground vs Internal Actuator Short Diagnostic Rule: A P0261 'Circuit Low' can be caused by the wiring harness rubbing against the metallic valve cover, OR by internal dielectric breakdown inside the injector solenoid/piezo stack. Unplug the Cylinder 1 injector: if P0261 immediately flips to P0201 (Open Circuit), the wiring harness and ECM driver are 100% HEALTHY-the injector itself is shorted internally to ground! If P0261 remains with the injector completely unplugged, the wiring harness wire is pinched to ground.
Electrical & Hydraulic Physical Benchmarks
Step-by-Step Workshop Diagnostic Protocol
Unplug Diagnostic Flip Test (Isolating Harness vs Injector)
Turn the ignition Key-ON with the engine stopped. Clear stored trouble codes. Unplug the electrical connector from the Cylinder 1 fuel injector while monitoring live scan tool codes. If code P0261 immediately clears and transforms into P0201 (Cylinder 1 Circuit Open), the vehicle wiring harness and ECM driver are 100% HEALTHY-the injector itself is internally shorted to ground! If P0261 persists with the injector completely disconnected, the wiring harness is shorted to ground.
High-Voltage Megohmmeter (Insulation Resistance) Test
With the Cylinder 1 injector removed or disconnected, use an automotive insulation tester (Megohmmeter) set to 250V or 500V test voltage. Connect one lead to the metal injector body and the other to each terminal pin in turn. Insulation resistance must be greater than 10 MΩ (typically >100 MΩ). Any reading below 10 MΩ confirms internal ceramic or enamel insulation breakdown arcing to ground under load.
Precision Four-Wire Low-Resistance Coil Measurement
Using a milliohm meter or digital multimeter with lead-zeroing on the lowest ohms scale, measure resistance across the two pins of the Cylinder 1 injector: normal resistance for solenoid injectors is 0.20 Ω to 0.45 Ω @ 20°C; for piezo injectors, 180 kΩ to 220 kΩ. A reading of 0.0 Ω (dead short) indicates fused coil windings.
Harness Short-to-Ground Ohms Continuity Audit
If the unplug test indicated a harness fault, turn Key-OFF and disconnect the ECM main harness plug. Using a multimeter on ohms scale, measure resistance between the Cylinder 1 low-side control wire pin and vehicle chassis ground. Resistance must be infinite (OL). If resistance is low (<100 Ω), visually trace the harness over the valve cover, bellhousing, and intake manifold to locate rubbed-through insulation.
Connector Water Ingress & Pin Inspection
Inspect the Cylinder 1 connector seal and terminal cavities. Engine oil pooling from leaking valve cover gaskets or coolant from a leaking coolant flange can seep into the connector, creating an electrolytic short circuit between the high-voltage pin and engine ground. Clean thoroughly with electronic contact cleaner and inspect terminal pin retention.
Oscilloscope Ground-Side Switching Waveform Verification
Back-probe the low-side control wire with an oscilloscope. Crank the engine: verify that the low-side driver pulls the signal cleanly to ground during firing and releases cleanly with a sharp flyback voltage clamp. If the trace remains permanently flat at ground (0V), the internal ECM low-side driver MOSFET has failed shorted.
Component-Level BOM: Cylinder 1 Common Rail Injector Drive & Wiring Subsystem
Cylinder 1 Common Rail Injector Drive & Wiring Subsystem
0 445 110 369 / 0 445 116 059
High-speed electro-hydraulic fuel injector with calibrated pilot/main injection metering
1 928 498 056 / Tyco Junior Timer 2-Way
Provides positive terminal spring tension to withstand 150V injection pulse vibrations
OEM Heat-Shielded Injector Sub-Loom
Protects injector command lines from constant 120°C hot engine oil splash
Injector Solenoid & Piezo Resistance Inspector
Associated Fuel Injection Components
The following genuine OEM fuel pumps and common rail injectors are verified factory equipment for engines reporting fault protocol P0261. Cross-reference operating pressures and tightening torques before sub-assembly replacement:
0445110239BOSCH
0445110239 Injector: PSA 1.6 HDi Ford 1.6 TDCi Specs
View Technical Specs & Fitment →0445110369BOSCH
0445110369 Injector: VW 2.0 TDI EA189 CFFB CFHC Specs
View Technical Specs & Fitment →0445116024BOSCH
BOSCH 0445116024 Common Rail Piezo Injector for BMW N47 2.0d & N57 3.0d
View Technical Specs & Fitment →095000-5880Denso
095000-5880 Denso Toyota 2KD-FTV Injector: 23670-30050 Data
View Technical Specs & Fitment →28337917Delphi
28337917 Delphi Bobcat D24 Injector: 7030364 Specs & Data
View Technical Specs & Fitment →095000-8340Denso
095000-8340 Denso Mitsubishi 4D56 HP Injector: 1465A367 Data
View Technical Specs & Fitment →Cylinder 1 Injector IMA/QR Calibration & Driver Reset Procedure
Following replacement of the Cylinder 1 fuel injector or repair of the shorted wiring harness, execute the calibration routine:
1. Enter the new 6-to-30 digit alphanumeric calibration code (IMA / QR code) stamped on the top of the new Cylinder 1 injector into the ECM via scan tool.
2. Clear all stored trouble codes and ensure battery voltage is fully charged (>12.5 V).
3. Access scan tool 'Engine Control Module' -> 'Special Functions' -> select 'Reset Injector Driver Stage Fault Memory'.
4. Start the engine and let it idle at full operating temperature (coolant >80°C) for 5 minutes without touching the accelerator.
5. The ECM will perform smooth-running control (SRC) zero-fuel calibration cycles to re-balance cylinder torque.
6. Conduct a 15-minute road test through all gear ranges, verifying smooth idle, instant throttle response, and zero pending DTCs.
Differential Diagnosis & Related Faults
Injector Circuit/Open - Cylinder 1
Companion open-circuit fault on Cylinder 1; unplugging a shorted injector will transform P0261 into P0201, confirming the injector is bad.
Cylinder 1 Injector Circuit High
Opposite electrical circuit failure: occurs when the injector control wire is shorted to 12V battery power or 80V boost supply.
Cylinder 1 Misfire Detected
Direct mechanical consequence: because the ECM disables the shorted Cylinder 1 injector, Cylinder 1 fails to fire, setting misfire code P0301.
Workshop Field Case Studies
2015 Ford Focus 2.0 TDCi (DW10C)(168,000 km)
Frequently Asked Technical Questions
What does engine fault code P0261 mean?
Diagnostic Trouble Code (DTC) P0261 indicates that the Engine Control Module (ECM/PCM) has detected that the electrical voltage in the fuel injector control circuit for Cylinder 1 has fallen below calibrated operational thresholds, or that excessive current has passed directly to ground. In common rail systems, the injector is supplied with high voltage (80V to 200V) from the ECM boost converter, and the low side is switched to ground by a high-speed power MOSFET. DTC P0261 is stored when the low-side control line is shorted to vehicle chassis ground, an internal coil insulation breakdown shorts the actuator to the cylinder head, or the ECM's internal output driver detects an abnormally fast current rise.
What are the most common symptoms of P0261?
Violent engine shaking, severe shudder, and continuous single-cylinder misfire under all operating conditions, Significant loss of vehicle acceleration, sluggish throttle response, and inability to maintain highway cruising speeds, Illuminated Check Engine Light (MIL) accompanied by flashing glow plug warning light and ESP/traction warning, Heavy puffing of white or grey unburned diesel smoke from exhaust pipe during cold start and acceleration, Strong, pungent odor of raw diesel fuel surrounding the vehicle exhaust and engine bay, Diagnostic scan tool live data shows Cylinder 1 contribution balance pegged at maximum positive fuel trim (+4.5 to +6.0 mg/stroke).
What causes P0261 on a diesel engine?
Cylinder 1 injector low-side control wire pinched, chafed, or shorted to vehicle chassis ground against the cylinder head or valve cover; Internal dielectric breakdown or winding short to ground inside the Cylinder 1 fuel injector electromagnetic solenoid or piezo stack; Corroded, wet, or water-contaminated terminal pins inside the Cylinder 1 injector connector creating a conductive path to ground; Damaged or shorted internal low-side MOSFET power transistor inside the Engine Control Module (ECM); Engine wiring harness crushed or pinched under an engine bracket, alternator mount, or intake manifold flange during prior service; Insulation melting caused by wiring harness contact with the hot exhaust gas recirculation (EGR) pipe or turbocharger heat shield.
Is it safe to drive with code P0261 active?
🟡 Caution: Limp Mode Active / Service Soon
How much does it cost to fix fault code P0261?
Typical repair costs for fault code P0261 depend on the underlying root cause and diagnostic tier: Level 1 (Minor / Maintenance): $45 - $95 (Pinpoint Wiring Harness Pinch Point & Solder Heat-Shrink Repair) (Sensor cleaning, fuel filter renewal, fuse replacement, or harness contact cleaning.); Level 2 (Component Replacement): $220 - $520 (Cylinder 1 Injector Replacement if Internal Coil Shorted to Body) (Single component fix (e.g. pressure regulator valve, inlet metering unit, or reconditioned injector).); Level 3 (Major Sub-Assembly): $750 - $1,800 (ECU Power Stage Driver Repair or Complete Main Engine Harness) (High-pressure injection pump overhaul, new OEM injector set, or DPF assembly replacement.). Independent workshop benchmark rates. Data indicates over 70% of occurrences are resolved within Level 1 or Level 2 without replacing entire sub-assemblies.
What is the difference between code P0201 and code P0261?
P0201 is an OPEN circuit fault: current cannot flow because a wire is broken, a terminal pin is loose, or an internal coil winding has snapped. P0261 is a SHORT TO GROUND (Circuit Low) fault: current is escaping directly to the engine metal body before completing its normal path, either because the harness wire is pinched against metal or because the internal insulation inside the injector has broken down.
How does unplugging the injector prove whether the wiring or the injector is broken?
This is the fastest test in common rail diagnostics. If you unplug the injector and the code changes from P0261 (Circuit Low) to P0201 (Circuit Open), you have proven 100% that the wiring harness is NOT shorted to ground (because if the harness were shorted, unplugging the injector wouldn't change anything; the wire would still be touching ground). Therefore, the short was inside the injector itself, and replacing the injector will cure the car.
Can water in the engine bay cause trouble code P0261?
Yes, very frequently. If someone pressure-washes the engine bay or if water leaks past the scuttle panel drain onto the top of the engine, moisture can enter the injector harness connector. Because common rail injectors operate under high voltage (80V-200V), water acts as an electrical conductor, creating a conductive bridge between the terminal pin and the grounded cylinder head, triggering P0261.