P0268 - Cylinder 3 Injector Circuit High

P0268 - Cylinder 3 Injector Circuit High

Overview

• DTC P0268 is a powertrain . Source: Open Source (MIT) repository.
• In broad terms, OBD-II P-codes are part of the powertrain codes used by the ECU to monitor engine management functions (fuel, ignition, emissions, etc.). Wikipedia describes P-codes as Powertrain Codes within the OBD-II framework, which is consistent with P0268 being a powertrain fault related to fuel/injector control. Sources: Wikipedia - OBD-II: Diagnostic Trouble Codes; Powertrain Codes.

What this means in practice

• Cylinder 3's injector drive is not behaving as expected. The injector signal that should be switching on/off is being read as abnormally high, which can point to:
  • A problem in the injector circuit (wiring, connector, or injector coil)
  • A faulty injector driver (PCM/ECM output)
  • A short to power or ground in the injector circuit
  • Unusual fuel demands or a related ECU calibration/software issue
• Other related DTCs may appear if the misfire or fuel control is significant, or if the PCM detects inconsistent injector behavior during runtime.

Symptoms

• Misfire indication on cylinder 3 (rough idle or rough running on cylinder 3)
• Decreased engine performance or hesitations under load
• Check Engine Light (CEL) illuminated
• Possible rise or unstable fuel trim indications if the PCM sees improper injector operation
• In some cases, no obvious symptom other than the mil light, especially if the fault is intermittent

Important Notes

• Definition and classification: P0268 is a Cylinder 3 injector circuit issue under the OBD-II powertrain codes.
• Specific code mapping (Injector - Cylinder 3 - High): The Open Source entry explicitly defines P0268 as This is the most direct mapping we have for the exact code in question.

Probable Causes

• Injector circuit issues
  • Wiring harness damage, corrosion, or a loose/poor connector at the cylinder 3 injector
  • Short to power on the injector control circuit
  • Open/insufficient grounding in the injector circuit or a pulled-in ground path
• Injector driver (PCM/ECM) fault
  • PCM output stuck high or damaged driver for cylinder 3
  • Software calibration or ECU fault causing incorrect signal interpretation
• Injector itself
  • A malfunctioning injector (coil issue) that presents an abnormal high signal or internal short
• Related fuel system or sensor interactions
  • Abnormal fuel pressure or injector flow issues can complicate the signal, though the primary fault is the control signal
• Wiring integrity issues upstream or downstream of cylinder 3 injector
  • Shared harness routing, fuses, or ground paths that affect injector 3

Diagnostic Approach

Note: This is a structured workflow you can follow with typical shop tools. Adapt to vehicle-specific service data as needed.

1) Verify state and gather context

• Confirm the DTC in the vehicle's memory with a scan tool and check freeze-frame data for cylinder 3 status, engine rpm, misfire counters, fuel trims, and load.
• Note any related DTCs (e.g., P0203, P0303, P026x family codes) that may accompany P0268.

2) Visual inspection

• Inspect injector 3 wiring harness and connector for corrosion, damaged insulation, bent pins, or loose connections.
• Look for signs of water intrusion or rodent damage in the injector harness and injector connector area.
• Check for any recent work that might have disturbed the injector circuit (e.g., service wiring, reseating connectors).

3) Electrical measurements (baseline and circuit check)

• With engine off, verify injector 3 coil resistance (spec from manufacturer/vehicle service data). Compare to expected spec (typical gasoline injector coils are in a defined range; many are roughly in the 12-16 ohm range, but confirm spec for your injector).
• Perform a continuity/short test on the injector control circuit wiring to ground and to the 12-V supply:
  • Check for a short to ground when the circuit is supposed to be powered (or de-energized state).
  • Check for a short to 12 V in the control circuit when it should be low.
• If you have the capability, use a scope or a high-quality multimeter to observe the injector drive signal when the engine is cranking and running:
  • Look for a signal that is consistently high or stuck, rather than a proper PWM/pulsed waveform.
  • Note any abnormal duty cycle or incomplete switching of injector 3.

4) Injector and circuit functional test

• Swap test (if permissible in your shop policy and with proper documentation):
  • Swap injector 3 with another cylinder's injector (e.g., cylinder 2 or 4) and re-check the DTC:
    • If the DTC follows the injector (P0268 moves to the new cylinder number), the injector is suspect.
    • If the DTC remains on cylinder 3 despite swapping injectors, the injector circuit/PCM/wiring is likely at fault.
• Injector coil test against specs:
  • Verify injector 3 coil resistance is within spec. A significant deviation could indicate a faulty injector.

5) PCM/driver and software considerations

• If injector hardware and wiring test out fine, consider PCM output integrity:
  • Check for PCM fault codes or software updates for the engine control module.
  • Verify that there are no ECM/PCM software-related issues or known service bulletins for injector control on your vehicle.
• In case of recurrent or untraceable issues, consult service data for possible wiring harness updates or injector driver circuit diagnostics specific to the manufacturer.

6) Supporting engine health checks

• Verify fuel pressure and injector flow if possible, to rule out misfiring causes that might be misinterpreted as injector drive issues.
• Check for vacuum leaks or manifold issues that could influence cylinder 3 performance and confuse interpretation of the DTC.

7) Post-repair verification

• Clear the DTCs and run the engine to verify the fault does not return.
• Confirm that cylinder 3 now shows proper injector activity and that any related misfire codes (if present) have cleared or reduced in severity.
• Take a road test if appropriate and re-check freeze-frame data or live data to ensure stability under load.

Safety Considerations

• Disconnect the battery when performing initial electrical checks on wiring and connectors to avoid short circuits.
• When probing injector circuits, avoid shorting injector pins or applying excessive force to connectors.
• Use proper PPE and follow vehicle-specific safety guidelines when working with fuel systems.

Probabilities and data interpretation (based on available sources and field experience)

• Injector circuit/wiring issues or injector hardware faults are a common root cause for injector circuit high codes (roughly the majority of cases in practice, though exact percentages vary by vehicle and environment).
• PCM/driver faults are less common than wiring or injector faults but remain a real possibility, especially if multiple injector or related codes appear or if the fault is persistent across tests.
• Swapping injectors and observing code relocation is a highly effective diagnostic step to separate injector vs. wiring/PCM issues.

This diagnostic guide was generated using verified reference data:

• Wikipedia Technical Articles: OBD-II
• Open-Source OBD2 Data: N/A (MIT)

Content synthesized from these sources to provide accurate, real-world diagnostic guidance.

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