What Does P0285 Mean?
This code signals a cylinder 8 contribution or balance fault where cylinder 8 is producing insufficient torque compared to other cylinders. Found on V8+ engines, the ECM uses crankshaft acceleration analysis to detect the power deficit. The driver will experience rough running, vibration, reduced power, and possible increased exhaust emissions from incomplete combustion in cylinder 8.
Common Causes
35%
Cylinder 8 fuel injector failing — restricted flow, worn nozzle, or degraded spray pattern
25%
Mechanical compression loss on cylinder 8 — worn rings, valve problems, or gasket breach
20%
Electrical issue in cylinder 8 injector circuit reducing fuel delivery
12%
Intake charge imbalance specifically affecting cylinder 8
8%
Exhaust manifold crack or gasket leak at cylinder 8 reducing efficiency
Diagnostic Steps
1
Confirm the imbalance by monitoring all cylinder contribution rates in live data — verify that cylinder 8's deviation is consistent and beyond normal tolerance across varying engine speeds.
2
Perform a relative compression test using cranking RPM uniformity to screen all cylinders for mechanical issues without any disassembly required.
3
Swap the cylinder 8 injector with a known-good cylinder on the same bank, clear codes and adaptation values, then operate the engine — track whether the fault follows the injector.
4
If the fault remains at cylinder 8 after injector swap, conduct a cylinder leak-down test — 15% or less leakage is considered good; above 20% indicates a significant mechanical issue.
5
Inspect cylinder 8 combustion chamber with a borescope for carbon buildup, piston damage, valve seat erosion, or signs of coolant intrusion from a head gasket leak.
Estimated Repair Cost
$150 - $1,500
Parts + labor, varies by vehicle and location
This code signals a cylinder 8 contribution or balance fault where cylinder 8 is producing insufficient torque compared to other cylinders. Found on V8+ engines, the ECM uses crankshaft acceleration analysis to detect the power deficit. The driver will experience rough running, vibration, reduced po...
The most common cause of P0285 (Cylinder 8 Contribution/Balance Fault) is: Cylinder 8 fuel injector failing — restricted flow, worn nozzle, or degraded spray pattern
Typical repair costs for P0285 range from $150 to $1,500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Moderate concern — the vehicle is driveable with noticeably reduced power. On V8 engines, a single cylinder contribution fault is somewhat masked but still causes elevated exhaust temperatures. Repair before the condition worsens.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0285 to identify the root cause.
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Quick Info
Category
Powertrain
System
Fuel Injection / Engine Mechanical
Difficulty
Type
Generic (SAE)
Recommended Tools
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