Code
P0287
HUMMER
P — Powertrain
Cylinder 9 Contribution/Balance Fault
AI status
Completed
Completed
100%
Causes
- Faulty fuel injector (plugged, leaking, poor spray pattern) for cylinder 9
- Faulty ignition component for cylinder 9 (coil, spark plug, ignition lead)
- Low or no compression in cylinder 9 (mechanical wear, valve issue, head gasket)
- Wiring or connector fault to injector or ignition coil (open, short, high resistance)
- Fuel delivery problem (low rail pressure, clogged rail/feed to that injector)
- PCM/ECM fault or incorrect calibration
Symptoms
- Check Engine Light (MIL) on
- Possible rough idle or vibration at idle and low speed
- Poor engine performance or hesitation under load
- Reduced fuel economy
- Visible misfire data or stored misfire-related codes (e.g., P0309) on a scan tool
- Engine may run normally at times if the fault is intermittent
What to check
- Read and record freeze-frame data and all stored/trending DTCs with a capable scan tool
- Check for related misfire codes (P0309) and random/multiple misfire codes (P0300)
- Monitor live data: cylinder contribution/balance, individual cylinder misfire counts, short/long term fuel trims, O2 sensor activity, fuel rail pressure and injector pulse widths
- Visually inspect wiring and connectors at cylinder 9 injector and coil for damage, corrosion or loose pins
- Perform a basic ignition check: inspect spark plug and coil; look for arcing or oil contamination
- Measure fuel rail pressure and inspect fuel supply/filters
Signal parameters
- Cylinder 9 contribution or balance percentage (scan tool)
- Cylinder-specific misfire counts (per ignition cycle)
- Injector pulse width (ms) for cylinder 9
- Short-term and long-term fuel trim (bank-level)
- O2 sensor (downstream/upstream) voltage and switching behavior
- Fuel rail pressure (psi/bar) and fuel trim response
Diagnostic algorithm
- Retrieve all DTCs and freeze-frame data; save or print for reference. Clear codes and perform a controlled road/idle test to re-check reproducibility.
- Use a scan tool to monitor cylinder contribution, misfire counts and injector pulse width for cylinder 9 while the engine is running. Note patterns (constant vs intermittent).
- Visually inspect wiring, connectors and grounds for cylinder 9’s coil and injector. Repair any damage and reconnect securely. Check connector continuity and resistance.
- Swap known-good components where practical: exchange coil #9 with another cylinder’s coil and re-check contribution/misfire. If the fault follows the coil, replace the coil. Repeat similarly with the injector if safe and practical.
- Inspect and, if necessary, replace the spark plug for cylinder 9. Check for oil/fuel fouling or abnormal wear. Re-test.
- Measure fuel rail pressure and verify injector pulse width. If injector pulse is present but contribution is low, consider injector flow test, cleaning or replacement.
- Perform compression test and/or leak-down test on cylinder 9 and compare to other cylinders. If compression is low, pursue valve, head gasket or piston/ring repairs.
- Check cam/crank correlation and timing components (timing chain/belt, variable cam timing actuators). Repair as needed if timing is off.
- If electrical checks are normal and mechanical checks pass, consider ECM/PCM driver circuit testing or software update as a possible cause; consult manufacturer service information before replacing ECM.
- After repairs, clear DTCs and confirm that cylinder contribution and drivability are restored over a representative road test. Document findings and parts replaced.
Likely causes
- Failed or weak ignition coil on cylinder 9
- Carbon-fouled or damaged spark plug on cylinder 9
- Clogged or electrically failed fuel injector for cylinder 9
- Low compression due to valve leakage, burned valve or piston damage
- Damaged wiring harness or corroded connector at injector/coil #9
- Intermittent PCM driver circuit fault
Fault status
Status
P0287 — Cylinder 9 Contribution/Balance Fault. The PCM reports that cylinder 9 is contributing outside expected parameters compared with other cylinders; further diagnosis required to identify root cause.
Repair difficulty: Medium
Diagnostic time: 1.0-4.0 hours
Repair manuals
Manual library for HUMMER
138
Browse 138 HUMMER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.
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