P0301

Code

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

Views: UK: 55 EN: 78 RU: 82

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Page language: EN

Causes

Faulty spark plug in cylinder 1
Failed or weak ignition coil for cylinder 1
Faulty ignition wire(s) or distributor components (where applicable)
Open/short in coil/injector wiring or poor connector/ground
Clogged, leaking or intermittent fuel injector for cylinder 1
Low or inconsistent fuel pressure / failing fuel pump or regulator

Symptoms

Illuminated Check Engine Light (CEL) with stored P0301
Rough idle or shaking at idle
Poor acceleration or reduced engine power
Increased fuel consumption and black smoke/soot in exhaust under load
Hesitation, stumbling, or bucking during acceleration
Possible misfire-related vibrations that may be intermittent or constant

What to check

Retrieve DTCs and freeze-frame / live data with a scan tool; note conditions when misfire set (RPM, load, temp)
View cylinder-specific misfire counters / contribution balance to confirm cylinder 1 is the source
Visually inspect spark plug, ignition coil, wiring and connectors for corrosion, carbon tracking or damage
Inspect intake manifold and vacuum hoses for leaks; perform smoke test if available
Measure fuel rail pressure and compare to manufacturer specification
Swap ignition coil (or coil-on-plug) from cylinder 1 with another cylinder to see if misfire follows

Signal parameters

Cylinder contribution/misfire counters: cylinder 1 should be at or near zero misfires when running normally
Short-term fuel trim (STFT): large positive values (+10% or more) may indicate lean condition or injector/fuel issue; large negative values may indicate rich condition
Long-term fuel trim (LTFT): persistent offsets suggest fuel delivery or metering faults
Fuel rail pressure: steady and at manufacturer spec under both idle and loaded conditions
Ignition coil primary voltage/dwell and secondary spark energy: primary switching present and within spec; secondary resistance within expected range for the coil type
Injector pulse width and duty: injector is being commanded and pulse widths are consistent with other cylinders under same load

Diagnostic algorithm

Read and record all trouble codes, freeze-frame, and live data (misfire counters, fuel trims, fuel pressure, MAF, RPM).
Clear codes and perform a road or stationary test to reproduce and confirm misfire on cylinder 1.
Perform visual inspection: spark plug condition, coil/boot damage, wiring/connectors, signs of oil/coolant intrusion.
Swap cylinder 1 ignition coil with another cylinder; re-run and see if misfire follows the coil. If it does, replace the coil.
If coil swap does not follow fault, swap or perform an injector balance/test on cylinder 1 to determine injector operation. Clean or replace injector as required.
Check fuel pressure under static and loaded conditions to confirm adequate and stable fuel delivery; repair fuel system if outside spec.
Perform a wet compression test or full compression/leak-down test on cylinder 1 to evaluate mechanical health (rings, valves, head gasket).
Inspect intake manifold and vacuum system; use smoke test or spray (safe method) to locate leaks. Repair if leak found.
Test camshaft and crankshaft sensors and their wiring; verify timing is correct and there are no timing chain/belt jumps.
Clean/inspect MAF and related intake sensors, verify TPS operation and scan for related sensor codes (P0100-series, P0110-series, P0340/P0335, P0171/P0174).
After any repair, clear codes and verify repair by road testing until code does not return and misfire counters are cleared.
If issue persists after above steps, proceed to deeper diagnostics (oscilloscope inspection of coil/injector waveforms, ECU/PCM testing, specialist mechanical inspection).

Likely causes

Worn or fouled spark plug in cylinder 1
Failed ignition coil or poor coil-to-spark-plug connection
Clogged or failed fuel injector on cylinder 1
Low fuel pressure or fuel delivery problem
Vacuum leak near intake runner for cylinder 1 or intake gasket leak
Low compression or mechanical damage in cylinder 1

Fault status

⚠️ Status

Misfire detected on cylinder 1 (P0301). Ignition, fuel, air intake, sensor or mechanical faults are possible—systematic testing required to identify root cause.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.5 - 4.0 hours

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