P0278

Cylinder 6 Injector Circuit High

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

In plain language — no jargon

The engine control unit detected that cylinder 6's fuel injector is receiving too much electrical voltage, like a faucet stuck in the open position. This prevents the injector from controlling fuel delivery properly.

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Symptoms You May Notice

3 known symptoms for this code
Engine misfires or runs rough on cylinder 6
Reduced fuel economy and black smoke from exhaust
Check Engine Light illuminated
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How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECM monitors the voltage and current flow through the cylinder 6 injector circuit. During normal operation, the injector receives a controlled pulse of voltage to open briefly. A 'high' fault occurs when the voltage exceeds the normal operating threshold, indicating an open circuit, shorted wiring, or failed injector driver.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
Injector Circuit Voltage 0-14.5V with controlled pulse timing >14.5V sustained or circuit resistance too low
Injector Resistance 12-16 ohms typical <8 ohms or open circuit (infinite resistance)
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Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
Injector wiring connector
Inspect and reseat the connector at cylinder 6 injector to eliminate corrosion or loose connections.
2
Fuel injector harness
Check wiring for pinched, chafed, or damaged insulation that may cause a short to voltage.
3
Fuel injector assembly
Replace the cylinder 6 injector if resistance testing shows it is open or shorted internally.
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When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code P0278 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 P0278

What happens after you fix the fault

Once the fault is repaired, P0278 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.