P0291

Cylinder 10 Contribution/Balance Fault

Powertrain Fuel and Air Metering Cylinder Balance 🟡 Moderate — Fix within a week ⚠️ Drive with Care
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What This Actually Means

In plain language — no jargon

Cylinder 10 isn't pulling its weight—it's not contributing power like it should compared to other cylinders. Think of it like one person in a tug-of-war team not pulling as hard as everyone else.

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Symptoms You May Notice

3 known symptoms for this code
Engine misfire or rough idle
Reduced fuel economy and power loss
Check Engine Light illuminated
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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECU monitors fuel trim and ignition timing corrections for each cylinder by analyzing oxygen sensor and knock sensor data. When cylinder 10's contribution deviates significantly from the bank average, it triggers a balance fault. The ECM compares each cylinder's efficiency against a learned baseline.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
Cylinder 10 Fuel Trim Variance Within ±5% of bank average Exceeds ±10% deviation from other cylinders
Cylinder 10 Combustion Efficiency 85-100% contribution ratio Below 75% of expected output
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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
Spark plug
Replace spark plug in cylinder 10; fouled or worn plugs are the most common cause.
2
Fuel injector
Clean or replace the fuel injector for cylinder 10 if clogged or leaking.
3
Ignition coil
Swap or test the ignition coil assigned to cylinder 10 for weak spark output.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code P0291 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.

Safety note: OBD-II codes identify the system or circuit where a fault was detected — they do not always identify the exact failed component. A professional mechanic using live sensor data will diagnose the root cause more accurately than replacing parts based on the code alone.
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How to Clear Code P0291

What happens after you fix the fault

Once the fault is repaired, P0291 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.

The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.

✅ Safe to Clear When
  • Fault has been diagnosed and repaired
  • You want to confirm the repair worked
  • Code appeared after a sensor was cleaned
⚠️ Do Not Clear When
  • Preparing for an emissions/PUC test
  • Root cause is still undiagnosed
  • Check engine light is flashing
Emissions test note: Clearing codes resets OBD readiness monitors. Most vehicles need 50–100 km of mixed driving before monitors complete. Do not clear codes immediately before an emissions or PUC inspection.