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Home / DTC / P1340 — Igniter Circuit Malfunction No 8

P1340 — Igniter Circuit Malfunction No 8

Detailed page for trouble code P1340.

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Code

P1340

LEXUS P — Powertrain

Igniter Circuit Malfunction No 8

Brand: LEXUS
Type: P — Powertrain
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Page language: EN

Causes

  • Faulty igniter or ignition coil (cylinder 8)
  • Open, short, or high-resistance wiring/connectors between ECM and igniter/coil
  • Poor or corroded ground or power supply to the igniter/coil
  • Loose or damaged coil/igniter connector pins
  • Intermittent wiring damage (chafing, rodent bite)
  • Faulty ECM or ignition driver circuitry

Symptoms

  • Malfunction Indicator Lamp (MIL) illuminated
  • Engine misfire on cylinder 8 or rough idle
  • Reduced engine power and poor acceleration
  • Decreased fuel economy
  • Possible backfire or hesitation under load
  • Engine may run roughly at idle and cruise

What to check

  • Retrieve and record freeze frame and all stored codes with a diagnostic scan tool
  • Visually inspect wiring harness, connectors, and coil/igniter for damage, corrosion, melted insulation or loose pins
  • Check battery voltage and main engine grounds
  • Perform a wiggle test on harness/connectors while monitoring live data or watching for code return
  • Measure connector pin voltage and ground at the coil/igniter connector with key on and engine cranking
  • Swap coil/igniter with a known-good cylinder (if practical) to see if code follows the component

Signal parameters

  • Supply voltage to coil/igniter: ~battery voltage with key ON (approx. 12 V)
  • Coil primary resistance: typically ~0.5–2 ohms (varies by coil design) — consult model spec
  • Coil secondary resistance: typically several kilo-ohms (varies) — consult model spec
  • Control signal from ECM: pulsed driver (either switched ground or switched +) synchronized to ignition timing; frequency and pulse width vary with RPM
  • Expected waveform: clean switching edges and consistent pulse timing; no missing pulses on cylinder 8

Diagnostic algorithm

  1. Read and record all DTCs and freeze frame data. Note related misfire or cam/crank codes.
  2. Clear codes and attempt to reproduce. Monitor for returning P1340 and any misfire counters (cylinder 8).
  3. Visually inspect the igniter/coil, connector, and wiring for damage, corrosion, burned pins or loose connections.
  4. Verify battery voltage and engine/chassis grounds; repair any low-voltage or poor-ground issues.
  5. With key ON, measure reference supply voltage at the coil/igniter connector; with engine cranking/running check for the control signal (use DVM for presence or oscilloscope for waveform).
  6. Measure coil primary and secondary resistance and compare to specifications. Replace if out of range.
  7. Swap the suspect igniter/coil with another cylinder’s unit. If the code/misfire follows the component, replace the failed part.
  8. Check continuity and resistance of the control and ground wires between the ECM and igniter; repair any opens or shorts.
  9. If wiring and coil are good but driver signal is absent or abnormal, test the ECM output driver and power/ground pins. Refer to service manual for pinouts and bench tests.
  10. After repair, clear codes and road-test. Re-scan to confirm code does not return and that driveability is restored.

Likely causes

  • Failed igniter/coil unit for circuit 8
  • Connector corrosion or poor mating at the igniter coil connector
  • Short to ground or to battery on the igniter control wire
  • Bad chassis/engine ground affecting igniter return
  • ECM output stage fault (rare)

Fault status

⚠️ Status
Malfunction in igniter/ignition coil driver circuit for circuit number 8 detected by ECM. MIL on; possible misfire or poor running.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

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