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Home / DTC / P0309 — Cylinder 9 Misfire Detected

P0309 — Cylinder 9 Misfire Detected

Detailed page for trouble code P0309.

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Code

P0309

Generic P — Powertrain

Cylinder 9 Misfire Detected

Brand: Generic
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Faulty spark plug in cylinder 9
  • Faulty ignition coil or coil pack for cylinder 9
  • Clogged, leaking, or electrically faulty fuel injector on cylinder 9
  • Low compression or mechanical damage in cylinder 9 (valve, piston, head gasket)
  • Faulty wiring or connector to injector or ignition coil
  • Vacuum leak near cylinder 9 or intake manifold gasket leak

Symptoms

  • Check Engine Light (MIL) illuminated
  • Rough idle or vibration at idle
  • Loss of power or poor acceleration
  • Higher-than-normal fuel consumption
  • Intermittent or persistent misfire P0309 stored
  • Possible hard start or stalling

What to check

  • Read and record freeze frame data and pending codes; confirm P0309 is current
  • Inspect spark plug condition and gap for cylinder 9
  • Swap ignition coil from cylinder 9 with another cylinder to see if misfire follows coil
  • Swap fuel injector (or use known-good injector) or perform injector balance/flow test
  • Perform a compression test or a cylinder leak-down test on cylinder 9
  • Check wiring and connectors for coils and injectors for damage, corrosion, or poor contact

Signal parameters

  • Misfire detection: increased misfire counter for cylinder 9 reported by ECM
  • Crankshaft speed variation waveform on crankshaft position sensor during misfire
  • Cylinder 9 short-term fuel trim (STFT) may be high or low relative to others
  • Long-term fuel trim (LTFT) changes if misfire persists
  • Fuel injector pulse width (ms) for cylinder 9 — should match similar cylinders when commanded
  • Primary ignition voltage/coil secondary waveform showing weak spark or no spark

Diagnostic algorithm

  1. Verify code: Clear codes and perform a test drive to confirm P0309 returns. Note misfire conditions (idle, load, cold).
  2. Retrieve live data: monitor misfire counters, fuel trims, fuel rail pressure, and sensor data while reproducing misfire.
  3. Visual inspection: check spark plug, coil, injector wiring and connectors for cylinder 9. Repair any damaged connectors or pin corrosion.
  4. Ignition swap test: swap the coil (or coil pack lead) from cylinder 9 to another cylinder. If misfire follows the coil, replace the coil.
  5. Injector test: listen for injector pulse, perform a back-probe to verify injector pulse, and consider swapping injectors or performing an injector flow/balance test.
  6. Compression/leak-down: perform a compression or leak-down test on cylinder 9 and compare to adjacent cylinders. If low, proceed with mechanical diagnosis (valve, piston rings, head gasket).
  7. Fuel and air checks: confirm correct fuel pressure and check for vacuum leaks near cylinder 9. Repair as needed.
  8. Spark plug check/replace: inspect plug for fouling or damage; replace plug if out of spec and retest.
  9. Check timing and sensors: verify cam/crank timing and inspect cam/crank position sensors and timing components for issues.
  10. After repairs: clear codes and confirm repair with road test and re-scan. If intermittent, perform extended monitoring or cabin/drive cycle tests.
  11. Safety note: When testing ignition circuits, use insulated tools and follow manufacturer safety procedures. When performing compression or leak-down tests, follow engine-specific procedures.

Likely causes

  • Worn/failed spark plug in cylinder 9
  • Failed ignition coil for cylinder 9 (most common on coil-on-plug systems)
  • Clogged or failed fuel injector on cylinder 9
  • Open/short in wiring or poor connector at coil or injector
  • Low compression in cylinder 9 (rings, valves, head gasket)

Fault status

⚠️ Status
Misfire detected on cylinder 9. ECM recorded inconsistent combustion events for cylinder 9 and set diagnostic trouble code P0309. Investigate ignition, fuel, and mechanical causes specific to cylinder 9.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-3.0 hours
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Code

P0309

GWM P — Powertrain

- The order of ignition of 9 cylinders is broken

Brand: GWM
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Faulty spark plug in cylinder 9
  • Faulty ignition coil or coil pack for cylinder 9
  • Clogged, leaking, or electrically faulty fuel injector on cylinder 9
  • Low compression or mechanical damage in cylinder 9 (valve, piston, head gasket)
  • Faulty wiring or connector to injector or ignition coil
  • Vacuum leak near cylinder 9 or intake manifold gasket leak

Symptoms

  • Check Engine Light (MIL) illuminated
  • Rough idle or vibration at idle
  • Loss of power or poor acceleration
  • Higher-than-normal fuel consumption
  • Intermittent or persistent misfire P0309 stored
  • Possible hard start or stalling

What to check

  • Read and record freeze frame data and pending codes; confirm P0309 is current
  • Inspect spark plug condition and gap for cylinder 9
  • Swap ignition coil from cylinder 9 with another cylinder to see if misfire follows coil
  • Swap fuel injector (or use known-good injector) or perform injector balance/flow test
  • Perform a compression test or a cylinder leak-down test on cylinder 9
  • Check wiring and connectors for coils and injectors for damage, corrosion, or poor contact

Signal parameters

  • Misfire detection: increased misfire counter for cylinder 9 reported by ECM
  • Crankshaft speed variation waveform on crankshaft position sensor during misfire
  • Cylinder 9 short-term fuel trim (STFT) may be high or low relative to others
  • Long-term fuel trim (LTFT) changes if misfire persists
  • Fuel injector pulse width (ms) for cylinder 9 — should match similar cylinders when commanded
  • Primary ignition voltage/coil secondary waveform showing weak spark or no spark

Diagnostic algorithm

  1. Verify code: Clear codes and perform a test drive to confirm P0309 returns. Note misfire conditions (idle, load, cold).
  2. Retrieve live data: monitor misfire counters, fuel trims, fuel rail pressure, and sensor data while reproducing misfire.
  3. Visual inspection: check spark plug, coil, injector wiring and connectors for cylinder 9. Repair any damaged connectors or pin corrosion.
  4. Ignition swap test: swap the coil (or coil pack lead) from cylinder 9 to another cylinder. If misfire follows the coil, replace the coil.
  5. Injector test: listen for injector pulse, perform a back-probe to verify injector pulse, and consider swapping injectors or performing an injector flow/balance test.
  6. Compression/leak-down: perform a compression or leak-down test on cylinder 9 and compare to adjacent cylinders. If low, proceed with mechanical diagnosis (valve, piston rings, head gasket).
  7. Fuel and air checks: confirm correct fuel pressure and check for vacuum leaks near cylinder 9. Repair as needed.
  8. Spark plug check/replace: inspect plug for fouling or damage; replace plug if out of spec and retest.
  9. Check timing and sensors: verify cam/crank timing and inspect cam/crank position sensors and timing components for issues.
  10. After repairs: clear codes and confirm repair with road test and re-scan. If intermittent, perform extended monitoring or cabin/drive cycle tests.
  11. Safety note: When testing ignition circuits, use insulated tools and follow manufacturer safety procedures. When performing compression or leak-down tests, follow engine-specific procedures.

Likely causes

  • Worn/failed spark plug in cylinder 9
  • Failed ignition coil for cylinder 9 (most common on coil-on-plug systems)
  • Clogged or failed fuel injector on cylinder 9
  • Open/short in wiring or poor connector at coil or injector
  • Low compression in cylinder 9 (rings, valves, head gasket)

Fault status

⚠️ Status
Misfire detected on cylinder 9. ECM recorded inconsistent combustion events for cylinder 9 and set diagnostic trouble code P0309. Investigate ignition, fuel, and mechanical causes specific to cylinder 9.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-3.0 hours
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Code

P0309

HUMMER P — Powertrain

Cylinder 9 Misfire Detected

Brand: HUMMER
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Faulty spark plug in cylinder 9
  • Faulty ignition coil or coil pack for cylinder 9
  • Clogged, leaking, or electrically faulty fuel injector on cylinder 9
  • Low compression or mechanical damage in cylinder 9 (valve, piston, head gasket)
  • Faulty wiring or connector to injector or ignition coil
  • Vacuum leak near cylinder 9 or intake manifold gasket leak

Symptoms

  • Check Engine Light (MIL) illuminated
  • Rough idle or vibration at idle
  • Loss of power or poor acceleration
  • Higher-than-normal fuel consumption
  • Intermittent or persistent misfire P0309 stored
  • Possible hard start or stalling

What to check

  • Read and record freeze frame data and pending codes; confirm P0309 is current
  • Inspect spark plug condition and gap for cylinder 9
  • Swap ignition coil from cylinder 9 with another cylinder to see if misfire follows coil
  • Swap fuel injector (or use known-good injector) or perform injector balance/flow test
  • Perform a compression test or a cylinder leak-down test on cylinder 9
  • Check wiring and connectors for coils and injectors for damage, corrosion, or poor contact

Signal parameters

  • Misfire detection: increased misfire counter for cylinder 9 reported by ECM
  • Crankshaft speed variation waveform on crankshaft position sensor during misfire
  • Cylinder 9 short-term fuel trim (STFT) may be high or low relative to others
  • Long-term fuel trim (LTFT) changes if misfire persists
  • Fuel injector pulse width (ms) for cylinder 9 — should match similar cylinders when commanded
  • Primary ignition voltage/coil secondary waveform showing weak spark or no spark

Diagnostic algorithm

  1. Verify code: Clear codes and perform a test drive to confirm P0309 returns. Note misfire conditions (idle, load, cold).
  2. Retrieve live data: monitor misfire counters, fuel trims, fuel rail pressure, and sensor data while reproducing misfire.
  3. Visual inspection: check spark plug, coil, injector wiring and connectors for cylinder 9. Repair any damaged connectors or pin corrosion.
  4. Ignition swap test: swap the coil (or coil pack lead) from cylinder 9 to another cylinder. If misfire follows the coil, replace the coil.
  5. Injector test: listen for injector pulse, perform a back-probe to verify injector pulse, and consider swapping injectors or performing an injector flow/balance test.
  6. Compression/leak-down: perform a compression or leak-down test on cylinder 9 and compare to adjacent cylinders. If low, proceed with mechanical diagnosis (valve, piston rings, head gasket).
  7. Fuel and air checks: confirm correct fuel pressure and check for vacuum leaks near cylinder 9. Repair as needed.
  8. Spark plug check/replace: inspect plug for fouling or damage; replace plug if out of spec and retest.
  9. Check timing and sensors: verify cam/crank timing and inspect cam/crank position sensors and timing components for issues.
  10. After repairs: clear codes and confirm repair with road test and re-scan. If intermittent, perform extended monitoring or cabin/drive cycle tests.
  11. Safety note: When testing ignition circuits, use insulated tools and follow manufacturer safety procedures. When performing compression or leak-down tests, follow engine-specific procedures.

Likely causes

  • Worn/failed spark plug in cylinder 9
  • Failed ignition coil for cylinder 9 (most common on coil-on-plug systems)
  • Clogged or failed fuel injector on cylinder 9
  • Open/short in wiring or poor connector at coil or injector
  • Low compression in cylinder 9 (rings, valves, head gasket)

Fault status

⚠️ Status
Misfire detected on cylinder 9. ECM recorded inconsistent combustion events for cylinder 9 and set diagnostic trouble code P0309. Investigate ignition, fuel, and mechanical causes specific to cylinder 9.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-3.0 hours
Repair manuals

Manual library for HUMMER

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Code

P0309

LAND ROVER P — Powertrain

ignition failure of Cylinder 9 detected

Brand: LAND ROVER
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Faulty spark plug in cylinder 9
  • Faulty ignition coil or coil pack for cylinder 9
  • Clogged, leaking, or electrically faulty fuel injector on cylinder 9
  • Low compression or mechanical damage in cylinder 9 (valve, piston, head gasket)
  • Faulty wiring or connector to injector or ignition coil
  • Vacuum leak near cylinder 9 or intake manifold gasket leak

Symptoms

  • Check Engine Light (MIL) illuminated
  • Rough idle or vibration at idle
  • Loss of power or poor acceleration
  • Higher-than-normal fuel consumption
  • Intermittent or persistent misfire P0309 stored
  • Possible hard start or stalling

What to check

  • Read and record freeze frame data and pending codes; confirm P0309 is current
  • Inspect spark plug condition and gap for cylinder 9
  • Swap ignition coil from cylinder 9 with another cylinder to see if misfire follows coil
  • Swap fuel injector (or use known-good injector) or perform injector balance/flow test
  • Perform a compression test or a cylinder leak-down test on cylinder 9
  • Check wiring and connectors for coils and injectors for damage, corrosion, or poor contact

Signal parameters

  • Misfire detection: increased misfire counter for cylinder 9 reported by ECM
  • Crankshaft speed variation waveform on crankshaft position sensor during misfire
  • Cylinder 9 short-term fuel trim (STFT) may be high or low relative to others
  • Long-term fuel trim (LTFT) changes if misfire persists
  • Fuel injector pulse width (ms) for cylinder 9 — should match similar cylinders when commanded
  • Primary ignition voltage/coil secondary waveform showing weak spark or no spark

Diagnostic algorithm

  1. Verify code: Clear codes and perform a test drive to confirm P0309 returns. Note misfire conditions (idle, load, cold).
  2. Retrieve live data: monitor misfire counters, fuel trims, fuel rail pressure, and sensor data while reproducing misfire.
  3. Visual inspection: check spark plug, coil, injector wiring and connectors for cylinder 9. Repair any damaged connectors or pin corrosion.
  4. Ignition swap test: swap the coil (or coil pack lead) from cylinder 9 to another cylinder. If misfire follows the coil, replace the coil.
  5. Injector test: listen for injector pulse, perform a back-probe to verify injector pulse, and consider swapping injectors or performing an injector flow/balance test.
  6. Compression/leak-down: perform a compression or leak-down test on cylinder 9 and compare to adjacent cylinders. If low, proceed with mechanical diagnosis (valve, piston rings, head gasket).
  7. Fuel and air checks: confirm correct fuel pressure and check for vacuum leaks near cylinder 9. Repair as needed.
  8. Spark plug check/replace: inspect plug for fouling or damage; replace plug if out of spec and retest.
  9. Check timing and sensors: verify cam/crank timing and inspect cam/crank position sensors and timing components for issues.
  10. After repairs: clear codes and confirm repair with road test and re-scan. If intermittent, perform extended monitoring or cabin/drive cycle tests.
  11. Safety note: When testing ignition circuits, use insulated tools and follow manufacturer safety procedures. When performing compression or leak-down tests, follow engine-specific procedures.

Likely causes

  • Worn/failed spark plug in cylinder 9
  • Failed ignition coil for cylinder 9 (most common on coil-on-plug systems)
  • Clogged or failed fuel injector on cylinder 9
  • Open/short in wiring or poor connector at coil or injector
  • Low compression in cylinder 9 (rings, valves, head gasket)

Fault status

⚠️ Status
Misfire detected on cylinder 9. ECM recorded inconsistent combustion events for cylinder 9 and set diagnostic trouble code P0309. Investigate ignition, fuel, and mechanical causes specific to cylinder 9.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-3.0 hours
413

Browse 413 LAND ROVER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

LAND ROVER

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+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
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