You can take the car to autozone and have their scanner read the code
for you for free.

CD

tiki <ryankilg@gmail.com> wrote in news:59545f34-aff6-43f1-baba-
73215f80da11@f47g2000hsd.googlegroups.com:

http://www.nissanhelp.com may be of some help.
My Haynes manual doesn't list any "138" code for that model year.
It does for 2000 and newer models;

P0138   O2 sensor;high voltage (bank 1 sensor 2)

What engine do you have in that car? 1.6L,1.8L,2.0L?

if it's the downstream,2nd O2S,it could mean a bad catalytic converter.
the 2nd O2S checks on the performance of the cat.

you can't clean O2 sensors.

Mileage of the car would help,too.
O2 sensors last about 60-100K miles,and can get sluggish before that.

OEM sensors are the way to go,not those universal replacement sensors.

I have the factory manual for 1998 Sentra 200SX equipped with the 2.0L,
SR engine.

Here's what it says:

DTC P0138

Rear Heated Oxygen Sensor (Max. Voltage Monitoring)

Component Description:

The rear heated oxygen sensor, after three way catlyst, monitors the
oxygen level in the exhaust gas.  Even if switching characteristics of
the front heated oxygen sensor are shifted, the air fuel ratio is
controlled to stoichiometric, byt the signal from the rear heated oxygen
sensor.  The sensor is made of ceramic zirconia.  The zirconia generates
voltage approximately 1V in richer conditions to 0V in leaner
conditions.  Under normal conditions the rear heated oxygen sensor is
not used for engine control operations. --

The rear heated oxygen sensor has a much longer switching time between
the rich and lean than the front heated oxygen sensor.  The oxygen
storage capacity before the three way catalyst causes the longer
switching time.  ECM monitors whether the maximum voltage of the sensor
is sufficiently high during various conditions such as fuel-cut.

DTC 1105

Manifold Absolute Pressure (MAP)/ Barometric Pressure (BARO) Switch
Solenoid Valve

Component Description:

This system allows the absolute pressure sensor to monitor either
ambient barometric pressure or intake manifold pressure.  The MAP/BARO
switch solenoid valve switches between two passages by ON-OFF pulse
signals from the ECM.  (One passage is from the air duct, the other is
from the intake manifold.)  Either ambient barometric pressure or intake
minforld pressure is applied to the absolute pressure monitor.

The MAP/BARO switch solenoid valve switches its air flow passage
according to the voltage signal sent from the ECM.  Whem voltage is
supplied from the ECM, the MAP/BARO switch solenoid turns "ON".  Then,
the absolute pressure sensor can monitor the ambient barometric
pressure.  When voltage is not supplied from the ECM, the MAP/BARO
switch solenoid valve turns "OFF".  Then, the sensor monitors intake
manifold pressure.

Short Description.  These systems really operate by magic.  Your car is
only and needs some $$$$ to feel better.

Jim