Code
P1356
OLDSMOBILE
P — Powertrain
IC Output High Pulse Detected When Grounded Cyl 6
AI status
Completed
Completed
100%
Causes
- Short to battery voltage on the IC/coil driver circuit for cylinder 6
- Open or high-resistance ground on the IC or coil primary
- Failed ignition coil (primary or internal short) on cylinder 6
- Faulty ignition control module / coil driver transistor
- Damaged, corroded, or disconnected wiring/connector at cylinder 6
- PCM/ECM internal driver fault (less common)
Symptoms
- MIL/Check Engine light illuminated
- Repeated or consistent misfire on cylinder 6 (rough idle, hesitation)
- Reduced power and poor acceleration under load
- Single-cylinder misfire trouble codes (P0306) in addition to P1356
- Possible hard start or extended cranking if driver stuck open
What to check
- Read stored/freeze-frame data and confirm P1356 along with any misfire codes (e.g., P0306)
- Visually inspect harness, connectors, and boots at cylinder 6 coil and IC/ignition module for corrosion, pin damage, or melted insulation
- Backprobe coil primary lead for cylinder 6 and compare to a known-good cylinder
- Check for continuity between the IC output pin and the coil primary; check for shorts to battery voltage and to ground
- Measure resistance of the coil primary and secondary against specification
- Check connector terminals for oil/water intrusion and secure pin fit
Signal parameters
- Expected idle amplitude: near battery voltage (~12 V) when driver is off, near 0 V (ground) when driver actively grounds the coil primary
- Pulse timing: one pulse per ignition event for cylinder 6, synchronized with crank/cam position
- Dwell/pulse width: varies with RPM and load (typically a few milliseconds at idle, longer/shorter as RPM/load change)
- Fault condition: a steady or pulsed high voltage present when the circuit should be grounded (unexpected high-level when ground commanded)
Diagnostic algorithm
- Confirm code and related codes, note freeze-frame data and engine conditions when code set.
- Visual inspection: check wiring, connectors, coil boots and IC/ignition module for damage, corrosion, melted wiring or water intrusion at cylinder 6.
- Swap test: swap the cylinder 6 ignition coil with a known-good coil from another cylinder. If code or misfire follows the coil, replace the coil.
- Backprobe and test: with ignition on/cranking, backprobe the coil primary and the IC output. Use a DVOM to check for unexpected steady battery voltage when the driver should be grounding, and use an oscilloscope if available to view pulse waveform and timing.
- Measure coil primary resistance and compare to spec. Check continuity between IC output terminal and coil primary, and check for shorts to battery or ground.
- Inspect/repair connector pins or wiring harness as needed (repair insulation, replace pins, remove corrosion).
- If wiring and coil test good, test or replace the ignition control module/coil driver. If a separate PCM driver is used and suspected, follow manufacturer procedures to test or substitute a known-good module/PCM.
- After repairs clear codes and road-test under varied conditions to confirm P1356 does not return and misfire symptoms are resolved.
Likely causes
- Shorted wiring between IC output and battery voltage for cylinder 6
- Failed ignition coil on cylinder 6
- Faulty ignition control module (driver)
- Corroded/poor connector at coil or IC causing intermittent high signal
Fault status
Status
IC output for cylinder 6 was measured or detected at a high voltage pulse when the circuit was expected to be grounded; indicates a short to voltage, failed coil or driver, or wiring/connector fault on the cylinder 6 ignition circuit.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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