Code
P0296
HUMMER
P — Powertrain
Cylinder 12 Contribution/Range Fault
Views:
UK: 11
EN: 37
RU: 12
AI status
Completed
Completed
100%
Causes
- Ignition failure on cylinder 12 (bad coil, spark plug, spark plug wire)
- Fuel injector fault (stuck, leaking, clogged, or electrical)
- Low or uneven compression (mechanical damage, valve, ring, or head gasket leak)
- Wiring or connector open/short to injector or ignition coil
- Fuel delivery problem (low rail pressure or clogged supply) affecting that cylinder
- Intake leak or valve timing issue causing poor cylinder filling
Symptoms
- Check Engine MIL illuminated
- Rough idle or vibration at idle
- Reduced engine power and acceleration
- Poor fuel economy
- Engine misfire felt or recorded on scan tool for cylinder 12
- Increased exhaust emissions or smell of raw fuel
What to check
- Read stored and pending trouble codes plus freeze-frame data with a scan tool
- Check for related codes (P0300-series misfire codes, injector or ignition circuit codes)
- Visually inspect wiring and connectors at coil and injector for damage or corrosion
- Check spark plug condition and gap on cylinder 12
- Compare fuel trim values and O2 sensor data between cylinders if available
- Check fuel rail pressure against manufacturer spec
Signal parameters
- Misfire/cylinder contribution: expected ~0 contribution difference between cylinders; cylinder 12 should match others
- Misfire count (per cylinder): expected 0; any repeating counts indicate misfire
- Long/short term fuel trim (LTFT/STFT): typically within ±10%; large deviation may indicate fueling issue
- Injector pulse width: changes consistent with load; no pulse = injector circuit fault
- Ignition coil resistance: compare to spec and to a known good coil
- Fuel rail pressure: within manufacturer spec under idle and load (example typical range 40–60 psi for many systems)
Diagnostic algorithm
- Connect a professional scan tool. Record P0296 plus any other codes and freeze-frame data (RPM, load, fuel trims, temp).
- Look for related misfire codes (P0300, P03xx) and injector/ignition circuit codes (P020x, P03xx).
- Perform a visual inspection: wiring, connectors, harness chafing, oil or coolant contamination on coil/injector.
- Swap coil/spark plug from cylinder 12 with another known-good cylinder. Re-scan for code movement to the other cylinder.
- Swap injector from cylinder 12 with another cylinder (or command injector pulse and observe). If the fault follows the injector, suspect the injector or its circuit.
- Perform a cylinder contribution or cylinder balance test with the scan tool to quantify cylinder 12 output relative to others.
- Check fuel rail pressure and fuel delivery under idle and load. Repair fuel supply issues before further cylinder-specific repairs.
- Perform wet and dry compression or a leak-down test on cylinder 12 to check for mechanical faults (valves, rings, head gasket).
- Inspect intake manifold gasket and vacuum lines around cylinder 12 for leaks; verify valve timing and cam/crank sensor signals.
- If wiring or connector faults are found, repair wiring, clean or replace connectors, then re-test.
- Replace failed component(s) confirmed by tests (coil, plug, injector, gasket, etc.), clear codes and perform a test drive to verify repair.
- If no fault found and intermittent only, check for software/PCM updates and review manufacturer TSBs; consider further bench tests or dealer-level diagnostics.
Likely causes
- Failed ignition coil on cylinder 12
- Worn or fouled spark plug in cylinder 12
- Injector stuck closed or leaking on cylinder 12
- Low cylinder compression (burned valve, broken ring, blown head gasket)
- Damaged injector/coil harness or poor connector pin contact
- Intermittent cam/crank sensor or timing variation affecting cylinder firing
Fault status
Status
Cylinder 12 contribution/range out of expected limits. Indicates a cylinder-specific misfire or imbalance. Inspect ignition, fuel injector, compression, wiring/connectors, and related sensors.
Repair difficulty: Medium
Diagnostic time: 1.5-3.5 hours
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