P1315

Code

BUICK P — Powertrain

Ignition Coil 4 Primary Feedback Circuit

Brand: BUICK

Type: P — Powertrain

Views: UK: 19 EN: 41 RU: 22

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Page language: EN

Causes

Faulty ignition coil (coil pack/module) for cylinder 4
Open, short, or high-resistance wiring/connectors in coil 4 primary/ground/power circuit
Poor or intermittent battery/ignition power to the coil
Corroded or loose connector pins or terminals
PCM/ECM fault or damaged driver transistor
Aftermarket ignition parts or improper coil replacement

Symptoms

Check Engine Light (MIL) illuminated
Rough idle or intermittent rough running
Single-cylinder misfire (cylinder 4) or multiple misfires
Reduced power, hesitation or surging under load
Increased fuel consumption and failed emissions test
Possible starting difficulty if fault is persistent

What to check

Read freeze frame and temporary/in-use data with a capable scan tool; note battery voltage and engine RPM when DTC set
Check for related codes (misfire codes P0304, P0300, and other coil circuit codes P035x)
Visual inspection of coil 4, connector, wiring harness, and nearby components for damage, corrosion, oil, or coolant contamination
Verify battery voltage at ignition on and during cranking (should be close to battery voltage)
Inspect and gently wiggle wiring and connectors while monitoring live data for intermittent changes
Measure coil primary resistance and compare to manufacturer specification

Signal parameters

Coil primary resistance (typical range): ~0.3–2.0 ohms (varies by coil design) — consult specific service data
Coil secondary resistance (typical range): ~6k–20k ohms (varies) — consult service data
Power feed: battery voltage (~11.5–14.5 V) present at coil power terminal with ignition on/cranking
Control/switch signal: PCM switches ground or +12 V (depending on design) — expected pulsed switching waveform (0 V to battery voltage) during operation
Dwell time: typically a few milliseconds (varies with RPM/load) — abnormal or absent pulses indicate fault
No open-circuit (infinite ohms) or hard short to battery/ground on signal or primary feed

Diagnostic algorithm

Connect a scan tool, confirm P1315 and any related codes. Note freeze frame and live data (RPM, voltage, misfire counts).
Perform a careful visual inspection of coil 4, connector, and harness for damage, oil or moisture contamination, bent pins, or corrosion.
Verify battery voltage at the coil power terminal with ignition ON and while cranking. Low battery or poor power feed can set the code.
With ignition OFF, disconnect coil 4 and check primary winding resistance between the coil’s primary terminals and secondary resistance per service spec. Replace coil if out of range.
Backprobe coil connector while cranking (or use oscilloscope) to observe the primary switching waveform: verify proper pulses, amplitude and dwell. No pulses or abnormal waveform indicates wiring or PCM driver issue.
Check continuity between the coil signal terminal and the PCM pin. Look for opens, shorts to voltage/ground, or high resistance. Repair damaged wires/connectors.
Perform a wiggle test on wiring/connector while monitoring live data for intermittent faults.
Swap coil 4 with another known-good coil (same type) and clear codes. If code follows the coil, replace the coil. If code stays on cylinder 4, suspect wiring or PCM.
If wiring and coil test good but fault persists, inspect PCM connector and grounds. As a last step, consider PCM testing/replacement following manufacturer procedure.
After repairs, clear codes and perform a full drive cycle to confirm the fault does not return.

Likely causes

Failed ignition coil on cylinder 4
Damaged or disconnected harness at coil connector
High resistance in power feed or ground to the coil
Shorted signal wire to battery or ground
Corroded terminal or poor contact at coil connector

Fault status

⚠️ Status

Ignition Coil 4 Primary Feedback Circuit — PCM detected abnormal or missing primary coil signal for cylinder 4. Inspect coil 4, its power/ground/signal wiring and connectors; verify coil and PCM operation.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1-3 hours

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