P0278 - Cylinder 6 Contribution/Balance Fault
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System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
The Engine Control Unit (ECU) monitors the crankshaft acceleration following each injection event to determine the torque contribution of each individual cylinder. Code P0278 is stored when the ECU detects that cylinder number 6 is contributing less power than the other cylinders. This is calculated using high-resolution data from the Crankshaft Position (CKP) sensor. In modern Common Rail diesel systems, the ECU uses 'Cylinder Balancing' or 'Smooth Running Control' to compensate for minor variations. If the required correction factor exceeds the calibrated limit (typically +/- 4-5 mg/stroke), the DTC is triggered.
Possible Causes
Clogged or faulty fuel injector for cylinder 6.
Internal engine mechanical issue (low compression, worn piston rings, or valve issues).
High resistance or corrosion in the wiring harness or connector to the injector.
Faulty fuel pressure regulator or restricted fuel filter affecting spray pattern.
Symptoms
Recommended Solution
- Visually inspect the wiring and connector for injector 6 for corrosion or chafing.
- Use a scan tool to check 'Cylinder Contribution' or 'Injection Quantity Correction' live data. A high positive value suggests the ECU is trying to compensate for a lean condition/clogged injector.
- Perform an injector leak-back test. High return flow indicates internal injector failure.
- Measure the injector's internal resistance with a multimeter (standard values are 0.2-0.5 Ohms for piezo or 12-14 Ohms for solenoid injectors, consult OEM specs).
- If mechanical failure is suspected: Perform a compression or leak-down test on cylinder 6.
- Replace the faulty injector and program the new IMA/IQA compensation code into the ECU using a diagnostic tool.
Mechanic's Tip
Before replacing expensive components, always double-check wiring and connections. 80% of all sensor faults are actually due to corroded contacts or broken wires.
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