P1278 Possible Causes
- Faulty Air/Fuel Ratio (A/F) Sensor 1 Bank 1
- Air/Fuel Ratio (A/F) Sensor 1 Bank 1 wiring harness or connectors are open or short-circuited
- Air/Fuel Ratio (A/F) Sensor 1 Bank 1 circuit poor electrical connection
- Fuel pressure
- Faulty fuel injector
- Intake air leaks
- Exhaust gas leaks
- Faulty PCV
- Faulty mass air flow meter
How is code P1278 repaired?
Start by checking the “Possible Causes” listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector pins.
Possible Symptoms
- Engine light on (or service engine soon warning light)
P1278 Meaning
The A/F sensor is a planar dual-cell limit current sensor. The sensor element of the A/F sensor combines a Nernst concentration cell (sensor cell) with an oxygen pump cell, which transports ions. It has a heating element within the element.
The sensor can accurately measure at λ=1, but also in both lean and rich ranges. With its control electronics, the sensor outputs a clear, continuous signal across a wide λ range (0.7 < λ < air).
Exhaust gas components diffuse through the diffusion gap at the oxygen pump electrode and Nernst concentration cell, where they are brought to thermodynamic equilibrium.
An electronic circuit controls the pump current through the oxygen pump cell so that the exhaust gas composition in the diffusion gap remains constant at λ=1. Therefore, the A/F sensor can indicate the air/fuel ratio via this pump current. Additionally, a heating element is integrated into the sensor to ensure the required operating temperature of 700 to 800°C (1,292 to 1,472°F).