Comprehensive Diagnostic Guide for OBD-II Code P0267

1) Code definition and scope

• What P0267 means: Cylinder 3 Injector Circuit Low. In other words, the ECU is detecting a fuel injector control circuit for cylinder 3 that is lower than expected (insufficient drive signal or voltage to the injector). This is a Powertrain/ fuel system diagnostic trouble code.
• Source reference: The Open Source OBD2 code definition states (Injector control circuit - cylinder 3 - low signal). This aligns with the standard P0267 definition.
• Context: P0267 is categorized under Powertrain Codes in OBD-II. The OBD-II system monitors various engine parameters and can set codes when injector circuits are not operating within spec.

2) Symptom patterns you may see

• Primary symptoms
  • Rough idle or stumble when engine is at idle, particularly on cold starts or during load changes.
  • Misfire indication localized to cylinder 3 (often corroborated by P0303 in many vehicles, though P0303 is a separate misfire code and not always present with P0267).
  • Potential drop in fuel economy or drivability irregularities under light to moderate load.
• Secondary indicators
  • Check Engine Light (CEL) illuminated.
  • Short-term/Long-term fuel trim shifts on cylinder 3 area (if the vehicle's data stream is available for you).
• Notes
  • These symptom patterns reflect common outcomes of injector-circuit faults in the field, which can be caused by wiring, injector, or PCM issues rather than a mechanical cylinder fault. Wikipedia's overview of how DTCs relate to engine controls supports this general behavior of sensor/actuator circuits generating codes when out of spec.

3) Likely causes (with practical probability guidance) (and common injector-circuit fault patterns), the probable causes for P0267 can be ranked as follows. Percentages are rough estimates to help prioritize diagnosis; they are not manufacturer-spec values and will vary by vehicle, engine, and geographic region.

• Wiring harness/connectors to injector 3 (damaged insulation, broken pin, corrosion, loose connector, bent terminals)
  • Approximate probability: 28%
• Injector 3 itself (mechanical failure, coil fault, internal short to ground, partial blockage)
  • Approximate probability: 22%
• PCM injector drive circuit/driver fault or related wiring from PCM to injector 3
  • Approximate probability: 18%
• Grounding issues or common ground problems affecting injector drive circuit
  • Approximate probability: 12%
• Fuel-supply related issues that affect injector performance indirectly (high fuel pressure/low pressure symptoms in the control path, or voltage drop under load)
  • Approximate probability: 8%
• Other or ambiguous conditions (uncommon PCM fault, intermittent wiring faults, etc.)
  • Approximate probability: 12%

Notes on these probabilities:

• These distributions reflect typical injector-circuit fault patterns observed in the field and align with the general concept that injector wiring/connectors and injector itself are common failure points, with electronics (PCM/driver) being a smaller but real contributor.
• do not include NHTSA complaint statistics for P0267; in their absence, these field-based probabilities offer practical guidance for diagnostic focus.

4) Diagnostic approach (step-by-step)

Preparation and Safety

• Ensure vehicle is on a level surface, cooling system safe, and battery is in good health.
• Follow standard safety procedures for electrical testing and fuel system work (disconnect battery when performing certain electrical tests; relieve fuel pressure if you open lines; never probe live fuel lines with flammable vapors present).
• Have the vehicle's service information/diagram for injector 3 wiring and its pinout handy (to identify the correct injector harness circuit).

Initial checks and data collection

• Confirm the DTC with a scan tool and pull freeze-frame data. Note engine RPM, load, coolant temperature, ignition status, fuel trims, and any other active codes.
• Check for related codes in the same bank or cylinder pattern (e.g., P0303, P0300, P0171/ P0174 for fuel trim). The OBD-II overview confirms that codes are used to indicate issues in the powertrain/fuel systems and may appear with other cylinder-related faults.
• Visual inspection: inspect injector 3 wiring harness and connector for obvious damage, corrosion, bent pins, loose fitment, or moisture intrusion. Inspect the injector connector seals and ensure proper seating.

Electrical tests (wiring and injector)

• Resistance check (injector 3):
  • With the ignition off, measure the resistance of injector 3 coil to verify it is within the vehicle's service spec and roughly equal to other injectors. If the resistance is abnormal (much higher or open), injector may be faulty.
  • If the resistance is in spec, the problem may be wiring or drive signal rather than a defective coil.
• Continuity and integrity test:
  • Check the injector circuit wiring from the PCM/ECU side to injector 3 for continuity and absence of opens or shorts to ground or battery voltage.
  • Inspect for insulation damage, coolant or oil contamination, or chafed wiring that could cause a signal-low condition.
• Connector and circuit integrity:
  • Disconnect and reconnect injector 3 harness connectors to ensure a solid mechanical contact. Re-torque or reseat as required per service specs.
• If available, perform an injector signal test:
  • Use a diagnostic oscilloscope or a dedicated injector test tool to observe the injector control signal (PWM/ground switch behavior). A low or unstable drive signal to the injector can corroborate a PCM-driver or wiring fault.
  • If a noid light or a scope shows a diminished or erratic signal on cylinder 3, focus on the wiring/driver path rather than the injector body itself.

Functional tests and diagnostic confirmation

• Swap test (cylinder-identification confirmation):
  • Swap injector 3 with injector from another cylinder (e.g., cylinder 2 or 4) and re-check the DTC and cylinder misfire behavior after clearing codes.
  • If P0267 follows the injector (now on a different cylinder), the injector is likely at fault. If the same cylinder 3 still reports P0267, the fault is likely in wiring or PCM drive to cylinder 3.
• Fuel system and performance checks:
  • Verify fuel pressure is within spec for the engine. While P0267 is an injector-circuit code, persistent fuel delivery issues can stress the injector drive or fuel-supply reliability.
  • Observe LTFT/STFT data if available. Large positive trims may indicate a broader fuel supply issue; a localized 3-specific fault supports injector-wiring or injector-drive issues.
• PCM/drive circuit check:
  • If wiring and injector appear okay, and the injector tests pass or show inconsistent results, evaluate the injector drive circuit/PCMs for potential internal faults or degraded output drivers. This becomes more likely if multiple injectors or related circuits show symptoms.

Repair Actions

• Primary fixes (most common, typically address the root cause quickly)
  1. Repair or replace damaged wiring or connectors to injector 3; repair harness damage, replace connectors, or restore proper pin seating.
  2. Replace injector 3 if testing confirms mechanical fault or if the injector coil is out of spec and non-repairable.
  3. Repair/replace PCM injector-driver signal path if diagnosed as a driver fault (rare but possible).
• Secondary checks
  • If the injector/wiring are good but the fault persists, re-check fuel system integrity and re-test after repairs. Re-scan to confirm code clear and confirm that the DTC does not return.
• If all else fails
  • Consider PCM/ECU as a potential fault source and follow manufacturer-recommended procedures for reflashing or replacement if other avenues have been exhausted and all wiring/injector tests pass.

Post-Repair Verification

• Clear the codes and perform a road test under varying loads, ensuring that injector 3 operates correctly and that no new codes reappear.
• Confirm free of P0267 and check for any related misfire codes (P0303) or abnormal fuel-trim behavior after drive cycles.
• Re-run freeze-frame data and drive-cycle tests to ensure under real-world operation the injector circuit remains within spec.

5) How to document and communicate findings

• Document observed symptoms, test results, wiring diagrams, injector resistance values, and any substitutions (injector swap data) used to verify diagnosis.
• Clearly indicate whether injector 3 wiring, injector, or PCM was identified as the fault, and the repair performed.
• Note any special vehicle considerations (engine type, cylinder count, bank orientation) since injector circuits can differ in layout across platforms.

6) Quick reference: key considerations and cross-checks

• DTC and cross-codes: P0267 is part of the injector-circuit family of codes; verify related injector codes or misfire codes (e.g., P0303) to understand if misfire patterns accompany P0267.
• Injector circuit context: Given the "low signal" description for cylinder 3, the fault is more likely on the drive signal path (PCM output or wiring) or the injector coil itself rather than simple mechanical failure of the cylinder.

7) What to tell the customer (concise summary)

• The vehicle has an injector circuit fault for cylinder 3, which could be caused by wiring/connectors, the injector itself, or the injector-drive circuitry in the PCM.
• We will inspect wiring and connectors, test the injector coil and drive signal, and may swap injectors to confirm whether the issue follows the injector or stays with cylinder 3's circuit.
• Repairs may involve replacing wiring harness/connectors, or replacing the injector, or addressing a PCM drive issue if confirmed.
• After repairs, we will re-check with a scan and a drive cycle to ensure the fault is resolved and no other related codes appear.

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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