Code
P0355
HUMMER
P — Powertrain
Ignition Coil 5 Control Circuit
AI status
Completed
Completed
100%
Causes
- Failed ignition coil (coil pack or coil-on-plug) for cylinder 5
- Open or short in the coil 5 wiring harness or connector
- Poor or corroded connector pins or grounds
- Loss of power supply to the coil circuit (fused feed)
- Internal failure of the PCM/ignition driver
- Faulty spark plug or mechanical issue causing apparent electrical problem
Symptoms
- Malfunction Indicator Lamp (MIL) or Check Engine Light ON
- Misfire felt at idle or under load, often stored as a P0305 (cylinder 5) or P0300
- Rough idle, hesitation, or reduced engine power
- Poor fuel economy
- Hard starting or stumbling on acceleration
- Possible engine backfire or increased emissions
What to check
- Retrieve freeze-frame and live-data with a scan tool; note misfire counters and PCM commands for coil 5
- Visually inspect coil 5, its connector, wiring harness, and ground for damage, corrosion, or loose pins
- Perform a wiggle test on the wiring and connector while monitoring the code or misfire counts
- Swap coil 5 with a known-good coil from another cylinder (if identical) and see if the code or misfire follows the coil
- Measure coil primary and secondary resistance and compare to manufacturer specs or typical ranges
- Verify battery voltage at the coil power feed and check for a switched ground/control signal from the PCM
Signal parameters
- Control type: PCM typically switches the coil primary to ground (low-side driver) to energize the coil
- Primary resistance (typical range for many coils): ~0.5–2.0 ohms (varies by coil type; consult spec)
- Secondary resistance (typical range): several kilo-ohms (varies widely by design; consult spec)
- Primary current during dwell: can be several amps (varies by engine control strategy)
- Control pulse: dwell and pulse width vary with RPM and load; PCM issues shorted-to-power or shorted-to-ground faults when pulse not seen or out-of-range
- Fault indications: open circuit (infinite resistance), short to ground or battery, or missing PCM drive pulses
Diagnostic algorithm
- Read and record all stored codes and freeze-frame data. Verify vehicle history and when the code sets (cold start, after warm-up, under load, intermittently).
- Visually inspect coil 5, connector, and wiring for damage, corrosion, pin push-out, or oil intrusion. Repair obvious issues before further testing.
- With ignition OFF, disconnect coil connector and inspect pins. Check for continuity between coil power pin and fused power source, and between coil ground/control pin and PCM (expect open to chassis ground when PCM not commanding).
- Measure coil primary and secondary resistance and compare to known-good or published values. Replace coil if out of range.
- Reconnect and back-probe connector or use appropriate adapter. With key ON (engine OFF), verify battery voltage on the coil power feed. Start engine or crank and observe PCM control signal on the coil control pin (use meter for pulse presence or scope for waveform).
- Perform a coil swap: move coil 5 to another cylinder. If misfire/code follows the coil, replace the coil. If it stays on cylinder 5, focus on wiring/PCM.
- Use a scope to inspect primary waveform for proper dwell, current draw, and absence of excessive voltage spikes. Look for intermittent dropouts while agitating harness.
- Repair any wiring faults, connector issues, or replace faulty coil. Clear codes and test-drive to confirm repair.
- If wiring and coil test good and symptom persists, follow manufacturer procedure to test PCM ignition driver and replace only if confirmed faulty.
Likely causes
- Defective ignition coil for cylinder 5
- Damaged or corroded connector or wiring to coil 5 (open/short/intermittent)
- Faulty ground or fused power feed to the coil rail
- PCM ignition driver fault (less common; verify wiring and coil first)
Fault status
Status
Ignition Coil 5 Control Circuit — open, short, or intermittent in coil/driver circuit
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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