Code
P0281
HUMMER
P — Powertrain
Cylinder 7 Contribution/Balance Fault
AI status
Completed
Completed
100%
Causes
- Faulty fuel injector (stuck, clogged, leaking) for cylinder 7
- Open/short or poor wiring/connector to injector or ignition coil
- Failed ignition coil or spark plug related to cylinder 7
- Low compression or mechanical cylinder damage (valve, piston, rings)
- Fuel delivery problems (low rail pressure or a blocked feed to that injector)
- ECM or driver circuit fault
Symptoms
- Malfunction Indicator Lamp (MIL) illuminated
- Rough idle or vibration at idle
- Reduced power, hesitation, or stumbling under load
- Single-cylinder misfire logging (cylinder 7)
- Higher fuel consumption and increased exhaust emissions
- Poor starting in some cases
What to check
- Connect a scan tool: read freeze frame and pending/confirmed misfire counts and related codes
- Monitor live data: cylinder contribution/adaptation values, misfire counters, short/long-term fuel trims, and O2 sensor readings
- Visual inspection of injector and coil harnesses, connectors, and engine grounds for damage or corrosion
- Check battery voltage and charging system under load
- Use a noid light or oscilloscope to verify injector pulse to cylinder 7 while cranking/running
- Measure injector DC resistance and compare to specification and to other injectors
Signal parameters
- Injector pulse width (ms) — compare cylinder 7 to other cylinders
- Cylinder 7 misfire counter (events/min or per drive cycle)
- Relative cylinder contribution/adaptation value (%) from scan tool
- Short-term and long-term fuel trim (%) — localized high positive trim may indicate lean contribution
- Fuel rail pressure (psi/bar) and fuel pressure return stability
- Battery voltage (V) under cranking and idle
Diagnostic algorithm
- Read and record freeze frame, confirmed/pending codes and misfire counts with a scan tool.
- Compare live cylinder contribution/adaptation values and misfire counters; confirm cylinder 7 is the only affected cylinder.
- Visually inspect wiring, connectors and engine grounds for cylinder 7; repair any damage or corrosion.
- Verify injector operation: use a noid light or scope to confirm pulse; measure injector resistance and compare to other cylinders.
- Swap coil and/or injector between cylinder 7 and a known good cylinder; if fault moves, replace the failing component.
- Check fuel supply: measure fuel rail pressure and inspect for feed restrictions or pressure instability.
- If electrical and fuel checks pass, perform compression or leak-down test on cylinder 7 to evaluate mechanical condition.
- Inspect valve timing and cam/crank sensor inputs if timing-related contribution loss is suspected.
- If all subsystem tests are normal, consider ECM/driver circuit diagnosis or replacement per manufacturer procedure.
- After repairs, clear codes and perform a road/test cycle while monitoring for return of P0281 and verifying normal cylinder contribution.
Likely causes
- Injector electrical fault (open/short/intermittent) or clogged injector
- Ignition problem (coil or spark plug) for cylinder 7
- Low compression or internal mechanical problem on cylinder 7
- Wiring/connector corrosion or intermittent connection to injector/coil
- Fuel rail pressure or feed issue affecting cylinder 7
Fault status
Status
P0281 — Cylinder 7 Contribution/Balance Fault: ECM detects reduced contribution from cylinder 7 relative to other cylinders. Check injector, ignition, wiring, fuel supply, and mechanical condition for cylinder 7.
Repair difficulty: Medium
Diagnostic time: 1–3 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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