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Old 01-03-2013, 12:38 PM   #3
Scooby Specialist
Member#: 131280
Join Date: Nov 2006
Chapter/Region: BAIC
Location: Northern California Hayward
2004 Impreza WRX


What does that mean?

The Heated Oxygen Sensor (2) located rear of catalytic converter produces an output signal relative to oxygen storage capacity of catalytic converter. Ho2S 2 signal is less active than signal produced by front oxygen sensor. This code sets when HO2 Sensor voltage is greater than 999 mV for more than 2 minutes (time depends on model. Could be as high as 4 minutes)

There may be no noticeable symptoms except for MIL illumination. Possible high fuel pressure can over rich the system.

A code P0138 may mean that one or more of the following has happened:

Faulty O2 sensor
Short to battery voltage in O2 sensor signal circuit
High fuel pressure (not as likely)

Possible Solutions

Here are some potential solutions:

Replace O2 sensor
Repair short to battery voltage in o2 sensor signal circuit
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