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Home / DTC / P0304 — Worn out spark plugs, ignition wires, coil(s), distributor cap and rotor (when applicable), Incorrect ignition timing, Vacuum leak(s), Low or weak fuel pressure, Improperly functioning EGR system, Defective Mass Air Flow Sensor, Defective Crankshaft and or Camshaft Sensor, Defective Throttle Position Sensor, Mechanical engine problems (i.e.—low compression, leaking head gasket(s), or valve problems)

P0304 — Worn out spark plugs, ignition wires, coil(s), distributor cap and rotor (when applicable), Incorrect ignition timing, Vacuum leak(s), Low or weak fuel pressure, Improperly functioning EGR system, Defective Mass Air Flow Sensor, Defective Crankshaft and or Camshaft Sensor, Defective Throttle Position Sensor, Mechanical engine problems (i.e.—low compression, leaking head gasket(s), or valve problems)

Detailed page for trouble code P0304.

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Code

P0304

AUDI P — Powertrain

Worn out spark plugs, ignition wires, coil(s), distributor cap and rotor (when applicable), Incorrect ignition timing, Vacuum leak(s), Low or weak fuel pressure, Improperly functioning EGR system, Defective Mass Air Flow Sensor, Defective Crankshaft and or Camshaft Sensor, Defective Throttle Position Sensor, Mechanical engine problems (i.e.—low compression, leaking head gasket(s), or valve problems)

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

Causes

  • Worn or fouled spark plug in cylinder 4
  • Faulty ignition coil or coil-on-plug
  • Damaged ignition wire, boot or distributor components (if applicable)
  • Incorrect ignition timing
  • Vacuum leak affecting cylinder 4 intake
  • Low or weak fuel pressure or faulty injector for cylinder 4

Symptoms

  • Check Engine Light (MIL) illuminated with P0304 stored
  • Rough idle or shaking at idle
  • Loss of power, hesitation or poor acceleration
  • Increased fuel consumption
  • Visible misfire when revving or under load
  • Possible audible popping or backfire

What to check

  • Read and record freeze frame and number of misfire counts with an OBD-II scanner
  • Scan for related codes (P0300, P0301–P0308, fuel trim, MAF, cam/crank sensor codes)
  • Inspect spark plug, coil and ignition boots for cylinder 4
  • Swap coil/injector between cylinder 4 and a known-good cylinder to see if code follows component
  • Measure fuel pressure at the rail and check injector pulse and resistance
  • Perform a compression or leak-down test on cylinder 4

Signal parameters

  • Crankshaft position sensor: consistent RPM pulses, no missing teeth or irregular timing
  • Cylinder contribution or balance data: low/zero contribution from cylinder 4
  • Short-term and long-term fuel trim (STFT/ LTFT): large positive trim suggests lean condition
  • MAF reading in g/s appropriate for RPM and load
  • Fuel rail pressure: within manufacturer spec (psi/bar)
  • Injector pulse width for cylinder 4 (ms) similar to other cylinders under same conditions

Diagnostic algorithm

  1. Retrieve freeze-frame data and related codes with a scan tool to determine when misfire occurs (idle, load, warm/cold).
  2. Visually inspect spark plug, coil pack/boot and wiring at cylinder 4; replace plug if fouled or worn.
  3. Swap the cylinder 4 ignition coil with a known-good cylinder. Clear codes and run to see if P0304 moves to the other cylinder (confirms coil/pack).
  4. If coil OK, swap the fuel injector with another cylinder or use an injector balance test. Monitor changes and inspect injector resistance and spray pattern.
  5. Check fuel pressure and fuel system health (fuel filter, pressure regulator). Repair if pressure out of spec.
  6. Perform a compression test or leak-down test on cylinder 4 to identify mechanical issues (low compression, leaking valve, or head gasket).
  7. Check intake system for vacuum or intake manifold leaks (use smoke test) near cylinder 4 and repair leaks.
  8. Verify MAF, MAP and TPS readings with live data; clean or replace MAF if contaminated and causing lean condition.
  9. Check crankshaft and camshaft position sensors and timing; inspect timing belt/chain condition and alignment.
  10. Inspect and test EGR operation; clean or replace if EGR is causing re-introduced exhaust flow and misfire.
  11. After repairs, clear codes and perform road test and re-scan to confirm misfire is resolved and no new related codes appear.

Likely causes

  • Faulty spark plug or ignition coil on cylinder 4
  • Clogged or leaking fuel injector for cylinder 4 or low fuel pressure
  • Vacuum leak or intake leak near cylinder 4
  • Low compression or mechanical valve/head gasket issue on cylinder 4
  • Faulty crank/cam position sensor or timing error
  • MAF sensor error producing incorrect air/fuel mixture

Fault status

⚠️ Status
Misfire detected on cylinder 4. ECM logged P0304 due to incomplete combustion events. Investigate ignition, fuel, air intake, sensors and mechanical condition of that cylinder.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-3 hours

Similar codes

P0300 P0301 P0302 P0303 P0305 P0306
Repair manuals

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Code

P0304

Generic P — Powertrain

Cylinder 4 Misfire Detected

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

Causes

  • Worn or fouled spark plug in cylinder 4
  • Faulty ignition coil or coil-on-plug
  • Damaged ignition wire, boot or distributor components (if applicable)
  • Incorrect ignition timing
  • Vacuum leak affecting cylinder 4 intake
  • Low or weak fuel pressure or faulty injector for cylinder 4

Symptoms

  • Check Engine Light (MIL) illuminated with P0304 stored
  • Rough idle or shaking at idle
  • Loss of power, hesitation or poor acceleration
  • Increased fuel consumption
  • Visible misfire when revving or under load
  • Possible audible popping or backfire

What to check

  • Read and record freeze frame and number of misfire counts with an OBD-II scanner
  • Scan for related codes (P0300, P0301–P0308, fuel trim, MAF, cam/crank sensor codes)
  • Inspect spark plug, coil and ignition boots for cylinder 4
  • Swap coil/injector between cylinder 4 and a known-good cylinder to see if code follows component
  • Measure fuel pressure at the rail and check injector pulse and resistance
  • Perform a compression or leak-down test on cylinder 4

Signal parameters

  • Crankshaft position sensor: consistent RPM pulses, no missing teeth or irregular timing
  • Cylinder contribution or balance data: low/zero contribution from cylinder 4
  • Short-term and long-term fuel trim (STFT/ LTFT): large positive trim suggests lean condition
  • MAF reading in g/s appropriate for RPM and load
  • Fuel rail pressure: within manufacturer spec (psi/bar)
  • Injector pulse width for cylinder 4 (ms) similar to other cylinders under same conditions

Diagnostic algorithm

  1. Retrieve freeze-frame data and related codes with a scan tool to determine when misfire occurs (idle, load, warm/cold).
  2. Visually inspect spark plug, coil pack/boot and wiring at cylinder 4; replace plug if fouled or worn.
  3. Swap the cylinder 4 ignition coil with a known-good cylinder. Clear codes and run to see if P0304 moves to the other cylinder (confirms coil/pack).
  4. If coil OK, swap the fuel injector with another cylinder or use an injector balance test. Monitor changes and inspect injector resistance and spray pattern.
  5. Check fuel pressure and fuel system health (fuel filter, pressure regulator). Repair if pressure out of spec.
  6. Perform a compression test or leak-down test on cylinder 4 to identify mechanical issues (low compression, leaking valve, or head gasket).
  7. Check intake system for vacuum or intake manifold leaks (use smoke test) near cylinder 4 and repair leaks.
  8. Verify MAF, MAP and TPS readings with live data; clean or replace MAF if contaminated and causing lean condition.
  9. Check crankshaft and camshaft position sensors and timing; inspect timing belt/chain condition and alignment.
  10. Inspect and test EGR operation; clean or replace if EGR is causing re-introduced exhaust flow and misfire.
  11. After repairs, clear codes and perform road test and re-scan to confirm misfire is resolved and no new related codes appear.

Likely causes

  • Faulty spark plug or ignition coil on cylinder 4
  • Clogged or leaking fuel injector for cylinder 4 or low fuel pressure
  • Vacuum leak or intake leak near cylinder 4
  • Low compression or mechanical valve/head gasket issue on cylinder 4
  • Faulty crank/cam position sensor or timing error
  • MAF sensor error producing incorrect air/fuel mixture

Fault status

⚠️ Status
Misfire detected on cylinder 4. ECM logged P0304 due to incomplete combustion events. Investigate ignition, fuel, air intake, sensors and mechanical condition of that cylinder.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-3 hours

Similar codes

P0300 P0301 P0302 P0303 P0305 P0306
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Code

P0304

GWM P — Powertrain

- The order of ignition of 4 cylinders is broken

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

Causes

  • Worn or fouled spark plug in cylinder 4
  • Faulty ignition coil or coil-on-plug
  • Damaged ignition wire, boot or distributor components (if applicable)
  • Incorrect ignition timing
  • Vacuum leak affecting cylinder 4 intake
  • Low or weak fuel pressure or faulty injector for cylinder 4

Symptoms

  • Check Engine Light (MIL) illuminated with P0304 stored
  • Rough idle or shaking at idle
  • Loss of power, hesitation or poor acceleration
  • Increased fuel consumption
  • Visible misfire when revving or under load
  • Possible audible popping or backfire

What to check

  • Read and record freeze frame and number of misfire counts with an OBD-II scanner
  • Scan for related codes (P0300, P0301–P0308, fuel trim, MAF, cam/crank sensor codes)
  • Inspect spark plug, coil and ignition boots for cylinder 4
  • Swap coil/injector between cylinder 4 and a known-good cylinder to see if code follows component
  • Measure fuel pressure at the rail and check injector pulse and resistance
  • Perform a compression or leak-down test on cylinder 4

Signal parameters

  • Crankshaft position sensor: consistent RPM pulses, no missing teeth or irregular timing
  • Cylinder contribution or balance data: low/zero contribution from cylinder 4
  • Short-term and long-term fuel trim (STFT/ LTFT): large positive trim suggests lean condition
  • MAF reading in g/s appropriate for RPM and load
  • Fuel rail pressure: within manufacturer spec (psi/bar)
  • Injector pulse width for cylinder 4 (ms) similar to other cylinders under same conditions

Diagnostic algorithm

  1. Retrieve freeze-frame data and related codes with a scan tool to determine when misfire occurs (idle, load, warm/cold).
  2. Visually inspect spark plug, coil pack/boot and wiring at cylinder 4; replace plug if fouled or worn.
  3. Swap the cylinder 4 ignition coil with a known-good cylinder. Clear codes and run to see if P0304 moves to the other cylinder (confirms coil/pack).
  4. If coil OK, swap the fuel injector with another cylinder or use an injector balance test. Monitor changes and inspect injector resistance and spray pattern.
  5. Check fuel pressure and fuel system health (fuel filter, pressure regulator). Repair if pressure out of spec.
  6. Perform a compression test or leak-down test on cylinder 4 to identify mechanical issues (low compression, leaking valve, or head gasket).
  7. Check intake system for vacuum or intake manifold leaks (use smoke test) near cylinder 4 and repair leaks.
  8. Verify MAF, MAP and TPS readings with live data; clean or replace MAF if contaminated and causing lean condition.
  9. Check crankshaft and camshaft position sensors and timing; inspect timing belt/chain condition and alignment.
  10. Inspect and test EGR operation; clean or replace if EGR is causing re-introduced exhaust flow and misfire.
  11. After repairs, clear codes and perform road test and re-scan to confirm misfire is resolved and no new related codes appear.

Likely causes

  • Faulty spark plug or ignition coil on cylinder 4
  • Clogged or leaking fuel injector for cylinder 4 or low fuel pressure
  • Vacuum leak or intake leak near cylinder 4
  • Low compression or mechanical valve/head gasket issue on cylinder 4
  • Faulty crank/cam position sensor or timing error
  • MAF sensor error producing incorrect air/fuel mixture

Fault status

⚠️ Status
Misfire detected on cylinder 4. ECM logged P0304 due to incomplete combustion events. Investigate ignition, fuel, air intake, sensors and mechanical condition of that cylinder.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-3 hours

Similar codes

P0300 P0301 P0302 P0303 P0305 P0306
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Code

P0304

HUMMER P — Powertrain

Cylinder 4 Misfire Detected

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

Causes

  • Worn or fouled spark plug in cylinder 4
  • Faulty ignition coil or coil-on-plug
  • Damaged ignition wire, boot or distributor components (if applicable)
  • Incorrect ignition timing
  • Vacuum leak affecting cylinder 4 intake
  • Low or weak fuel pressure or faulty injector for cylinder 4

Symptoms

  • Check Engine Light (MIL) illuminated with P0304 stored
  • Rough idle or shaking at idle
  • Loss of power, hesitation or poor acceleration
  • Increased fuel consumption
  • Visible misfire when revving or under load
  • Possible audible popping or backfire

What to check

  • Read and record freeze frame and number of misfire counts with an OBD-II scanner
  • Scan for related codes (P0300, P0301–P0308, fuel trim, MAF, cam/crank sensor codes)
  • Inspect spark plug, coil and ignition boots for cylinder 4
  • Swap coil/injector between cylinder 4 and a known-good cylinder to see if code follows component
  • Measure fuel pressure at the rail and check injector pulse and resistance
  • Perform a compression or leak-down test on cylinder 4

Signal parameters

  • Crankshaft position sensor: consistent RPM pulses, no missing teeth or irregular timing
  • Cylinder contribution or balance data: low/zero contribution from cylinder 4
  • Short-term and long-term fuel trim (STFT/ LTFT): large positive trim suggests lean condition
  • MAF reading in g/s appropriate for RPM and load
  • Fuel rail pressure: within manufacturer spec (psi/bar)
  • Injector pulse width for cylinder 4 (ms) similar to other cylinders under same conditions

Diagnostic algorithm

  1. Retrieve freeze-frame data and related codes with a scan tool to determine when misfire occurs (idle, load, warm/cold).
  2. Visually inspect spark plug, coil pack/boot and wiring at cylinder 4; replace plug if fouled or worn.
  3. Swap the cylinder 4 ignition coil with a known-good cylinder. Clear codes and run to see if P0304 moves to the other cylinder (confirms coil/pack).
  4. If coil OK, swap the fuel injector with another cylinder or use an injector balance test. Monitor changes and inspect injector resistance and spray pattern.
  5. Check fuel pressure and fuel system health (fuel filter, pressure regulator). Repair if pressure out of spec.
  6. Perform a compression test or leak-down test on cylinder 4 to identify mechanical issues (low compression, leaking valve, or head gasket).
  7. Check intake system for vacuum or intake manifold leaks (use smoke test) near cylinder 4 and repair leaks.
  8. Verify MAF, MAP and TPS readings with live data; clean or replace MAF if contaminated and causing lean condition.
  9. Check crankshaft and camshaft position sensors and timing; inspect timing belt/chain condition and alignment.
  10. Inspect and test EGR operation; clean or replace if EGR is causing re-introduced exhaust flow and misfire.
  11. After repairs, clear codes and perform road test and re-scan to confirm misfire is resolved and no new related codes appear.

Likely causes

  • Faulty spark plug or ignition coil on cylinder 4
  • Clogged or leaking fuel injector for cylinder 4 or low fuel pressure
  • Vacuum leak or intake leak near cylinder 4
  • Low compression or mechanical valve/head gasket issue on cylinder 4
  • Faulty crank/cam position sensor or timing error
  • MAF sensor error producing incorrect air/fuel mixture

Fault status

⚠️ Status
Misfire detected on cylinder 4. ECM logged P0304 due to incomplete combustion events. Investigate ignition, fuel, air intake, sensors and mechanical condition of that cylinder.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-3 hours

Similar codes

P0300 P0301 P0302 P0303 P0305 P0306
Repair manuals

Manual library for HUMMER

138

Browse 138 HUMMER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

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Code

P0304

MITSUBISHI P — Powertrain

No.4 cylinder misfire detected

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

Causes

  • Worn or fouled spark plug in cylinder 4
  • Faulty ignition coil or coil-on-plug
  • Damaged ignition wire, boot or distributor components (if applicable)
  • Incorrect ignition timing
  • Vacuum leak affecting cylinder 4 intake
  • Low or weak fuel pressure or faulty injector for cylinder 4

Symptoms

  • Check Engine Light (MIL) illuminated with P0304 stored
  • Rough idle or shaking at idle
  • Loss of power, hesitation or poor acceleration
  • Increased fuel consumption
  • Visible misfire when revving or under load
  • Possible audible popping or backfire

What to check

  • Read and record freeze frame and number of misfire counts with an OBD-II scanner
  • Scan for related codes (P0300, P0301–P0308, fuel trim, MAF, cam/crank sensor codes)
  • Inspect spark plug, coil and ignition boots for cylinder 4
  • Swap coil/injector between cylinder 4 and a known-good cylinder to see if code follows component
  • Measure fuel pressure at the rail and check injector pulse and resistance
  • Perform a compression or leak-down test on cylinder 4

Signal parameters

  • Crankshaft position sensor: consistent RPM pulses, no missing teeth or irregular timing
  • Cylinder contribution or balance data: low/zero contribution from cylinder 4
  • Short-term and long-term fuel trim (STFT/ LTFT): large positive trim suggests lean condition
  • MAF reading in g/s appropriate for RPM and load
  • Fuel rail pressure: within manufacturer spec (psi/bar)
  • Injector pulse width for cylinder 4 (ms) similar to other cylinders under same conditions

Diagnostic algorithm

  1. Retrieve freeze-frame data and related codes with a scan tool to determine when misfire occurs (idle, load, warm/cold).
  2. Visually inspect spark plug, coil pack/boot and wiring at cylinder 4; replace plug if fouled or worn.
  3. Swap the cylinder 4 ignition coil with a known-good cylinder. Clear codes and run to see if P0304 moves to the other cylinder (confirms coil/pack).
  4. If coil OK, swap the fuel injector with another cylinder or use an injector balance test. Monitor changes and inspect injector resistance and spray pattern.
  5. Check fuel pressure and fuel system health (fuel filter, pressure regulator). Repair if pressure out of spec.
  6. Perform a compression test or leak-down test on cylinder 4 to identify mechanical issues (low compression, leaking valve, or head gasket).
  7. Check intake system for vacuum or intake manifold leaks (use smoke test) near cylinder 4 and repair leaks.
  8. Verify MAF, MAP and TPS readings with live data; clean or replace MAF if contaminated and causing lean condition.
  9. Check crankshaft and camshaft position sensors and timing; inspect timing belt/chain condition and alignment.
  10. Inspect and test EGR operation; clean or replace if EGR is causing re-introduced exhaust flow and misfire.
  11. After repairs, clear codes and perform road test and re-scan to confirm misfire is resolved and no new related codes appear.

Likely causes

  • Faulty spark plug or ignition coil on cylinder 4
  • Clogged or leaking fuel injector for cylinder 4 or low fuel pressure
  • Vacuum leak or intake leak near cylinder 4
  • Low compression or mechanical valve/head gasket issue on cylinder 4
  • Faulty crank/cam position sensor or timing error
  • MAF sensor error producing incorrect air/fuel mixture

Fault status

⚠️ Status
Misfire detected on cylinder 4. ECM logged P0304 due to incomplete combustion events. Investigate ignition, fuel, air intake, sensors and mechanical condition of that cylinder.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-3 hours

Similar codes

P0300 P0301 P0302 P0303 P0305 P0306
406

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+100 karma for a short comment :)
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