What Does P2278 Mean?
The PCM has detected that the signals from the Bank 1 Sensor 3 and Bank 2 Sensor 3 oxygen sensors appear to be reversed or crossed. This indicates the sensors were likely installed on the wrong banks or the wiring is crossed.
Common Causes
50%
Oxygen sensors installed on wrong banks during previous repair
35%
Crossed or swapped wiring harness connectors
10%
Miswired repair or aftermarket installation
3%
PCM software issue or incorrect programming
2%
Damaged wiring causing cross-signal interference
Diagnostic Steps
1
Step 1: Verify sensor locations and confirm which physical sensor corresponds to each bank
2
Step 2: Trace wiring from each sensor to connector and verify correct bank assignment
3
Step 3: Monitor live data for both sensors simultaneously and observe which physical bank each responds to
4
Step 4: Check if sensors were recently replaced and may have been installed on wrong banks
5
Step 5: Swap sensors between banks or correct wiring connections as needed and clear codes
Estimated Repair Cost
$50 - $200
Parts + labor, varies by vehicle and location
The PCM has detected that the signals from the Bank 1 Sensor 3 and Bank 2 Sensor 3 oxygen sensors appear to be reversed or crossed. This indicates the sensors were likely installed on the wrong banks or the wiring is crossed.
The most common cause of P2278 (O2 Sensor Signals Swapped Bank 1 Sensor 3/Bank 2 Sensor 3) is: Oxygen sensors installed on wrong banks during previous repair
Typical repair costs for P2278 range from $50 to $200, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle is safe to drive. This is primarily a diagnostic concern that may affect emissions monitoring accuracy but poses no immediate safety risk.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P2278 to identify the root cause.
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Quick Info
Category
Powertrain
System
Emissions Control System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
