Code
P1315
LEXUS
P — Powertrain
Igniter Circuit Malfunction No 4
Views:
UK: 23
EN: 42
RU: 24
AI status
Completed
Completed
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Causes
- Failed ignition coil or integrated igniter for cylinder 4
- Damaged wiring or connector (open, short to power, short to ground) in the coil/igniter circuit
- Poor or corroded connector/terminal at the coil or ECM
- Faulty ECM/ignition driver output
- Intermittent loss of battery/ignition power or poor ground
- Contamination or heat damage to coil/igniter (oil, water, cracked housing)
Symptoms
- Check Engine Light (MIL) illuminated
- Rough idle or misfire (often cylinder 4)
- Reduced engine power and poor acceleration
- Hard start or no-start condition under some circumstances
- Possible intermittent misfire or stalling
What to check
- Retrieve freeze-frame and live data with a scan tool; note MIL, misfire counters and related codes (P0304)
- Verify battery voltage and charging system health before testing (low voltage can create false codes)
- Visually inspect coil No.4, connectors and harness for damage, contamination, corrosion or water intrusion
- Check for additional DTCs that point to wiring or ECM issues
- If safe, swap coil/igniter No.4 with another cylinder to see if fault follows the coil or stays on circuit
- Perform resistance checks and continuity on coil primary/secondary and between coil connector and ECM pins (with power removed)
Signal parameters
- Typical coil primary resistance (varies by model): approx. 0.2–2.0 Ω (consult OEM spec for exact value)
- Typical coil secondary resistance: approx. 5 kΩ–15 kΩ (model dependent)
- Igniter driver/ECM output: pulsed switching (ground or +12V) — expect 0–12 V waveform when cranking/running
- Dwell/time and pulse frequency vary with engine speed — an oscilloscope of primary waveform should show consistent pulses when cylinder should fire
- No short to battery or heavy short to ground on coil control circuit (low resistance indicates short)
Diagnostic algorithm
- Safety first: work with engine off/cool and battery secure; if performing live ignition tests, avoid contact with high voltage.
- Connect a capable scan tool and confirm P1315 along with any secondary codes; record freeze-frame and live data (RPM, voltage, misfire counts).
- Check battery voltage (12.4 V+ at rest, 13.5–14.5 V while charging). Low voltage can produce spurious igniter faults.
- Perform a visual inspection of coil No.4 and harness; unplug connector and look for corrosion, bent pins, oil/water intrusion, or heat damage.
- Swap coil/igniter No.4 with a known-good coil from another cylinder. Clear codes and run engine to see if P1315 moves with the coil (indicates coil/igniter fault) or stays on cylinder 4 (indicates wiring/ECM).
- Measure coil primary and secondary resistance per OEM spec. If out of range, replace coil/igniter.
- Check continuity between the coil harness pin and the ECM pin for the igniter driver and power/ground circuits; check for shorts to battery or ground.
- If wiring and coil check good, use a scope to view primary waveform at coil connector while cranking/running. Look for missing pulses, clipped waveforms or abnormal current draw.
- If ECM driver signal is absent or abnormal but wiring and coil are good, consider ECM fault — confirm with manufacturer diagnostic procedures before ECM replacement.
- After repairs, clear codes and road-test to verify the fault does not return and monitor for related misfire codes.
Likely causes
- Faulty ignition coil/igniter No.4
- Loose/corroded connector at the coil
- Open or shorted harness between ECM and coil No.4
- Shorted coil primary winding or internal igniter failure
Fault status
Status
Manufacturer-specific code: Igniter Circuit Malfunction No.4 — ECM detected abnormal signal or open/short in the igniter/ignition coil circuit for cylinder 4; may cause misfire and reduced engine performance.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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