Description

These DTCs are set when there is an open or short in the A/F sensor circuit, or if A/F sensor output drops. To detect these problems, the voltage of the A/F sensor is monitored when turn the ignition switch to the ON position, and the admittance (admittance is an electrical term that indicates the ease of flow of current) is checked while driving. If the voltage of the A/F sensor is between 0.6V and 4.5V, it is considered normal. If the voltage is out of the specified range, or the admittance is less than the standard value, the ECM will determine that there is a malfunction in the A/F sensor. If the same malfunction is detected in next driving cycle, the MIL will be illuminated and a DTC will be stored. The A/F sensor, which is located between the exhaust manifold and catalyst, consists of alloyed metal elements and a heater.

Depending on the engine operating conditions, the heater heats the sensor elements to activate them. Battery voltage is applied to the heater, the sensor ground is controlled by the ECM using a duty ratio. The sensor elements convert the oxygen concentration in the exhaust gas into voltage values to output. Based on the voltage, the ECM determines the air-fuel ratio and regulates the fuel injection volume depending on the air-fuel ratio and engine operating conditions. The voltage changes between 0.6V and 4.5V while the engine is running. If the air-fuel ratio is LEAN, which means the oxygen concentration in the exhaust gas is high, the voltage is high. If the air-fuel ratio is RICH, which means the oxygen concentration in the exhaust gas is low, the voltage is low.

Reference (System Diagram of Sensor 1):

EFI MAIN

From Battery o—o

Ground

A/F Sensor

Heater

HA1A

Sensor

HA1A

A1A-

A1A+

A1A+

A1A-

MREL

Duty Control

A140695E01

A/F Sensor Voltage

Element

Exhaust Gas

Cover

Alumina

Heater

Solid Electrolyte (Zirconia Element)

Platinum Electrode Atmospheric Air

12 13 14 15 16 17 18

Air-Fuel Ratio

A-A Cross Section

A107164E12

DTC No.

DTC Detection Condition

Trouble Area

P2237

Open in the circuit between terminals AF+ and AF- of the AF sensor while engine is running (2 trip detection logic)

• Open or short in A/F sensor (sensor 1) circuit

• ECM

P2238

Any of the following conditions are met (2 trip detection logic)

• AF sensor output drops while engine is running.

• Voltage difference between terminals AF+ and AF-is 0.1V or less.

• Open or short in A/F sensor (sensor 1) circuit

• ECM

DTC No.

DTC Detection Condition

Trouble Area

P2239

AF+ voltage more than 4.5 V (2 trip detection logic)

• Open or short in A/F sensor (sensor 1) circuit

• ECM

P2252

AF- voltage 0.5 V or less (2 trip detection logic)

• Open or short in A/F sensor (sensor 1) circuit

• ECM

P2253

AF- voltage more than 4.5 V (2 trip detection logic)

• Open or short in A/F sensor (sensor 1) circuit

• ECM

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