DTC: P1278

Search Bulletins/Recalls for P1278

Trouble diagnosis name: Air fuel ratio (A/F) sensor 1 (Bank 1) circuit slow response

Component Description

The A/F sensor is a planar dual-cell limit current sensor. The sensor element of the A/F sensor is the combination of a Nernst concentration cell (sensor cell) with an oxygen-pump cell, which transports ions. It has a heater in the element.

The sensor is capable of precise measurement λ= 1, but also in the lean and rich range. Together with its control electronics, the sensor outputs a clear, continuous signal throughout a wide λ range (0.7 < λ < air).

The exhaust gas components diffuse through the diffusion gap at the electrode of the oxygen pump and Nernst concentration cell, where they are brought to thermodynamic balance.

An electronic circuit controls the pump current through the oxygen-pump cell so that the composition of the exhaust gas in the diffusion gap remains constant at λ = 1. Therefore, the A/F sensor is able to indicate air/fuel ratio by this pumping of current. In addition, a heater is integrated in the sensor to ensure the required operating temperature of 700 - 800C (1,292 - 1,472F).

DTC detecting condition:

• The response (from RICH to LEAN) of the A/F (Bank 1) signal computed by ECM from A/F sensor 1 signal takes more than the specified time.

Possible cause:

• Harness or connectors (The A/F sensor 1 circuit is open or shorted.)
• Air fuel ratio (A/F) sensor 1
• Air fuel ratio (A/F) sensor 1 heater
• Fuel pressure
• Fuel injector
• Intake air leaks
• Exhaust gas leaks
• PCV
• Mass air flow sensor