Code
P1340
DS
P — Powertrain
Cylinder 4 ignition fail malfunction
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EN: 1
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AI status
Completed
Completed
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Causes
- Failed or weak ignition coil (coil‑on‑plug or coil pack) on cylinder 4
- Worn, fouled, damaged or incorrect spark plug in cylinder 4
- Open/shorted ignition wiring, connector or poor ground to cylinder 4 coil
- Faulty or plugged fuel injector for cylinder 4 (no fuel delivery)
- Low compression or mechanical problem in cylinder 4 (valve, piston, ring)
- Crankshaft/camshaft position sensor or timing/cam/crank correlation problem
Symptoms
- Check Engine MIL illuminated (DTC P1340 or related stored)
- Rough idle or noticeable misfire at idle
- Reduced engine power or hesitation under load
- Engine vibration or shaking, often felt from the engine bay
- Increased fuel consumption and higher exhaust emissions
- Possible audible popping/backfire in intake or exhaust
What to check
- Read and record all stored, pending and freeze‑frame data from the ECU. Note operating conditions when code set.
- Scan for related DTCs (P0304, P0300, P0354, P0350, cam/crank sensor codes) and address those first.
- Check battery and charging system voltage (engine running > 13 V; cranking voltage > 10 V).
- Visually inspect coil, spark plug, wiring harness and connector for damage, corrosion or oil contamination.
- Inspect and measure spark plug condition and gap; compare to OEM specification.
- Listen for injector operation with a stethoscope or use a noid light; check injector resistance against spec.
Signal parameters
- Misfire count / cylinder contribution — cylinder 4 should show increased misfire when fault active
- Ignition coil primary voltage during crank/run — should follow battery voltage (approx. battery level)
- Coil primary resistance and secondary resistance — compare to OEM specification for that coil
- Injector resistance (ohms) and injector pulse width (ms) during injection events
- Crankshaft/camshaft position signals — consistent, no missing or distorted pulses
- Short‑term and long‑term fuel trims — large trim changes can indicate fueling or combustion issues
Diagnostic algorithm
- Retrieve DTCs and freeze frame. Note engine temperature, RPM, load and voltage when code set.
- Inspect coil, spark plug and wiring for cylinder 4; replace obvious damaged parts.
- Swap the coil (and if applicable the spark plug) from cylinder 4 with a known good cylinder. Clear codes, run engine and check if misfire moves to the other cylinder. If it moves, replace the coil or plug.
- If misfire stays on cylinder 4, check fuel injector: listen for clicking, check resistance, use noid light or apply a known good injector to test.
- Check wiring harness and connectors for continuity, shorts to ground or power, and poor grounds between ECU and coil/injector.
- Use live data/oscilloscope to verify coil driver commands from ECU and examine coil primary/secondary waveforms for weak or absent spark.
- Perform compression or leak‑down test on cylinder 4 to rule out mechanical causes.
- If all hardware looks good, check cam/crank correlation and related sensors; update/reflash ECU software if a known bug exists.
- After repairs, clear codes and perform road test to confirm the fault does not return. Re‑scan to verify readiness and absence of related DTCs.
Likely causes
- Ignition coil failure on cylinder 4
- Bad or fouled spark plug in cylinder 4
- Wiring/connector fault to coil or injector for cylinder 4
- Clogged or failed injector causing no spray
- Local mechanical issue (low compression) in cylinder 4
Fault status
Status
Cylinder 4 ignition failure detected (misfire). Inspect ignition coil, spark plug, wiring and fuel delivery on cylinder 4; verify compression and ECU signals.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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