Comprehensive diagnostic guide for OBD-II code P0273

Disclaimer on code mapping

• P0273 is described in the available open-source mapping as: "Injector Circuit - Cylinder 5 - Low Signal." This is one mapping reference and may vary by engine family or OEM; some sources and general OBD-II coding overview on Wikipedia. See citations: Open Source mapping and Wikipedia OBD-II sections.

What This Code Means

• P0273 is categorized as a powertrain diagnostic trouble code related to the fuel injector circuit. Specifically, it indicates a problem with the injector drive signal in one cylinder (i.e., the PCM is not seeing the expected injector-operating signal). The issue can be a bad injector, a wiring/connector problem, a faulty injector driver in the PCM, or related electrical faults in the injector circuit. This aligns with the general understanding of injector-circuit diagnostics described in the OBD-II sections of Wikipedia (Diagnostic Trouble Codes; Powertrain Codes). Citations: Wikipedia - OBD-II: Diagnostic Trouble Codes; Wikipedia - OBD-II: Powertrain Codes; Open Source mapping cited above.

Symptoms a customer might report

• Check engine light is on (MIL).
• Rough idle, especially when the engine is cold or at low speed.
• Misfire-like symptoms on the affected cylinder (perceived as roughness, lack of smooth idle, stumbling, or intermittent hesitation).
• Decreased throttle response or reduced engine power.
• Possible increased fuel consumption or a noticeable drop in torque under load.
• In some cases, you may see related misfire codes (P030X for cylinder-specific misfires), but P0273 focuses on the injector-circuit condition for that cylinder.
  Note: Always check for additional DTCs that could indicate misfire, lean/rich conditions, or fuel-pressure concerns, as those can accompany injector-circuit problems.

Probable Causes

These are the common causes you'll see in practice when diagnosing a single-cylinder injector-circuit fault. Percentages are approximate and; no authoritative NHTSA frequency data is provided here.

• Faulty injector (mechanical/coil issue): 25-40%
  • The injector for the affected cylinder may be sticking, not opening consistently, or not delivering the correct pulse width due to internal coil failure.
• Wiring/connector to the injector (open/short, corrosion, poor connection): 25-40%
  • Damaged harness, pin corrosion, or a loose/mis-seated injector connector can produce a low or erratic control signal.
• Injector driver/PCM issue (injector driver circuit fault or PCM output problem): 10-20%
  • The engine control module's injector driver for the cylinder may be weak or failed, or there could be an intermittent internal fault.
• Electrical supply issues to the injector (power or ground problems): 5-15%
  • Intermittent power supply to the injector or a poor ground path can yield a low signal condition.
• Fuel-system issue limited to one cylinder (less common): 5-10%
  • While a rail or pump problem typically affects multiple cylinders, a severely restricted/blocked injector could mimic a circuit issue; however, this is less common than circuit/wiring problems for a single-cylinder code.

Pre-Diagnostic Checks

1) Confirm the code and cylinder mapping

• Note the cylinder number reported by your scan tool. If needed, cross-check with OEM wiring diagrams to confirm which cylinder corresponds to P0273 on this engine. The Open Source mapping explicitly links P0273 to "Cylinder 5 - low signal," but OEMs can differ. Wikipedia confirms P-codes as part of Powertrain codes, but exact cylinder mapping is OEM-specific.
• Check for any other codes (P030x misfires, fuel trim codes, P0171/P0174 lean/rich, or P0087/P009x fuel-pressure codes) that could provide context.

2) Gather operating data (live data)

• Look at injector-circuit data for the affected cylinder:
  • Injector pulse width / duty cycle compared to the other cylinders.
  • Battery voltage to the injector circuit (are you seeing a proper supply voltage?).
  • Injector ground signal (is there a ground reference?).
• Check for misfire indicators in freeze-frame data (RPM, load, throttle position, fuel trims, ignition timing if available).
• If the vehicle supports it, watch for a healthy injector signal waveform or a noid-light signal for the affected injector.

3) Quick electrical checks

• Inspect the injector connector and wiring for damage, corrosion, or loose pins at the injector and associated harness connectors.
• Wiggle-test the injector harness near the connector while monitoring the live data; note any intermittent changes in injector signal or misfire indication.
• Measure injector resistance (coil resistance) with a multimeter and compare to the manufacturer's specification. If the resistance is wildly out of spec or shows an open/short, replace the injector or the wiring harness as needed.
• Inspect power and ground circuits:
  • Confirm the injector's supply voltage is present when the engine is cranking/operating.
  • Verify a solid ground path for the injector circuit (check ground pins and common ground points).

4) Injector-specific tests

• Noid-light or oscilloscope test:
  • Use a noid light (or a proper oscilloscope) to verify the injector drive signal is present and correctly pulsing for the cylinder in question. If the signal is absent or abnormal, focus on the driver circuit or wiring.
• Swap-test (manual cylinder swap):
  • If feasible on the engine, swap the suspect injector with another cylinder's injector (or use a known-good injector on the cylinder). Clear codes and recheck. If the code moves to the new cylinder, the injector is at fault; if the code stays on the original cylinder, the issue is likely wiring/driver or PCM-related.
• Compare with other injectors:
  • Compare the affected injector's pulse width and duty cycle to the other injectors. A significantly different pattern supports an injector or driver/wiring issue for that cylinder.

5) Fuel-system and mechanical checks (contextual)

• Check overall fuel pressure to ensure the system meets specifications. If only one cylinder is affected and the rail pressure is normal, it points more toward the injector circuit rather than a system-wide fuel-pressure issue.
• Inspect the vacuum/engine mechanical condition (valve, piston, or ring issues) if misfire symptoms persist after injector-circuit diagnostics. While these are less likely to produce a low-signal code, they can cause similar rough-running symptoms.

6) PCM and related components

• If all injector-circuit tests are inconclusive and the injector and wiring appear sound, consider PCM injector-driver output integrity. Rarely, a defective PCM can cause injector-circuit faults in one cylinder.
• Re-seat/clean PCM and harness connectors to reduce resistance or intermittent contact.

7) Verify repair

• After repair or component replacement, clear the codes and perform an on-road or test-drive cycle to confirm the issue is resolved.
• Recheck live data to ensure the injector for the affected cylinder is now pulsing correctly and that no related misfire codes reappear.

Safety Considerations

• Relieve fuel-system pressure before removing fuel lines or connectors.
• Work in a well-ventilated area and away from flames or sparks.
• Disconnect the battery when performing wiring work near the PCM or high-current fuel components to avoid shorts or electrocution risk.
• Follow OEM procedures for injector-service procedures and torque specs.

Common repair options (ordered by likelihood)

• Replace the faulty injector (or the injector that tests as defective via resistance or PWM signal).
• Repair or replace the injector harness or connector (repairing corrosion, replacing damaged wiring, reseating connectors).
• Replace or repair injector driver circuits in the PCM (or use a known-good PCM if available (with caution and compatibility checks)).
• Correct fuel delivery issues if multiple cylinders are affected (fuel pump or rail issues could otherwise cause broad problems, though they're less likely to present as P0273 alone).
• Re-check and repair any underlying mechanical or vacuum issues contributing to poor combustion in the affected cylinder.

Notes on code interpretation and sources

• The concept of DTCs and their function in modern OBD-II systems is described in Wikipedia's OBD-II sections (Diagnostic Trouble Codes; Powertrain Codes), which cover how the system monitors parameters and reports faults. This provides the general framework for injector-circuit DTCs like P0273. Citations: Wikipedia - OBD-II: Diagnostic Trouble Codes; Wikipedia - OBD-II: Powertrain Codes.
• A specific mapping found in an open-source OBD2 code reference lists P0273 as
• Because cylinder assignments can vary by engine design, always verify the cylinder mapping for P0273 on the particular vehicle using OEM service information or your scan-tool's cylinder display if available. The general diagnostic approach remains focused on injector-circuit integrity, whether the fault is a bad injector, a wiring/connector issue, or a PCM driver problem.

Quick Checklist

• Confirm code and cylinder mapping; note any related codes.
• Review freeze-frame data and live data for injector PWM, engine RPM, fuel trims, and injector voltage.
• Inspect injector wiring and connectors for damage, corrosion, or loose connections.
• Measure injector resistance; compare to spec.
• Perform a noid-light/oscilloscope test to verify the injector drive signal presence and waveform.
• If possible, swap injectors or use a known-good injector on the affected cylinder to isolate the fault.
• Check overall fuel pressure and rail for issues that could affect a single injector signal.
• Inspect PCM injector-driver output integrity if injector and wiring tests are inconclusive.
• Clear codes and test-drive to verify repair; re-check for reoccurrence.

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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