Code
P1315
CHRYSLER
P — Powertrain
Ignition Coil 4 Primary Feedback Circuit
Views:
UK: 26
EN: 53
RU: 35
AI status
Completed
Completed
100%
Causes
- Failed ignition coil (coil #4)
- Damaged or corroded coil connector or pins
- Open, shorted, or high-resistance wiring in the coil #4 primary circuit
- Poor power or ground supply to the coil
- Faulty PCM ignition driver
- Intermittent wiring harness damage (pinch, chafe, rodent)
Symptoms
- MIL (Check Engine Light) ON with stored P1315
- Cylinder 4 misfire, rough idle
- Poor acceleration, hesitation under load
- Reduced fuel economy
- Possible hard start or stumble at idle
- Occasional intermittent misfire or stumble
What to check
- Read freeze frame and live data with a scan tool (cylinder misfire counts, coil driver status)
- Inspect coil #4 and connector for corrosion, oil, or damage
- Swap coil #4 with a known good coil from another cylinder and see if code follows
- Backprobe coil connector and check for battery voltage (key ON) and PCM driver pulse (cranking/running)
- Measure primary coil resistance and compare to spec
- Inspect wiring harness for chafing, breaks, or rodent damage
Signal parameters
- Primary coil resistance (typical modern coil: approx. 0.5–3.0 ohms; check OEM spec for exact value)
- Supply voltage to coil power pin: battery voltage (~11–14.5 V with engine running, key ON ~12V)
- PCM driver: low-side switch to ground — expect pulsed switching during cranking/running
- Primary waveform: sharp current ramps and abrupt collapse (square-ish pulses) when viewed on a scope; missing or abnormal pulses indicate fault
- No high-voltage measurement required for primary circuit checks, but caution: ignition secondary can carry several kV
Diagnostic algorithm
- Read and record codes, freeze frame, and misfire counters with a scan tool. Clear codes and attempt to reproduce.
- Visually inspect coil #4, connector, and harness for damage, oil contamination, bent pins, or corrosion. Repair as needed.
- Swap coil #4 with another cylinder's coil. If the P1315 (or misfire) follows the coil, replace the coil. If it stays with cylinder 4, continue wiring/PCM checks.
- With connector connected, backprobe power and ground pins at the coil. Verify constant battery voltage on the power feed (key ON) and good ground return. Check for intermittent voltage drop while wiggling harness.
- With an assistant cranking/engine running, backprobe the PCM driver pin and verify pulsed switching using a lab scope or a digital multimeter (frequency/pulse present while cranking).
- Measure primary coil resistance (coil removed or connector disconnected) and compare to OEM spec. Very high or infinite resistance indicates open coil; short to ground/other circuits indicates harness fault.
- Use an oscilloscope to view the primary waveform at the coil primary. Look for proper switching, consistent pulse shape, and current collapse. Abnormal waveform suggests coil or driver issue.
- If wiring is suspect, perform continuity and resistance checks from coil connector to PCM connector. Repair any opens/shorts, poor splices, or grounds.
- If wiring and coil test good but problem persists, verify PCM power/ground and consider PCM driver failure. Replace PCM only after all other causes are eliminated and reprogram if required.
- After repairs, clear codes and perform a road/test cycle to confirm the fault does not return.
Likely causes
- Bad coil #4 (most common)
- Loose/corroded connector or poor pin contact at coil
- Broken or shorted primary wire between coil and PCM
- Faulty ignition driver in PCM (less common)
Fault status
Status
MIL ON — DTC P1315 (Ignition Coil 4 Primary Feedback Circuit) stored. Possible cylinder 4 misfire and related drivability symptoms. Further diagnosis required.
Repair difficulty: Medium
Diagnostic time: 1-2 hours
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