Diagnostic Trouble Code (Dtc) P0138 O2 Sensor Circuit High Voltage (Bank 1 Sensor 2) - Isuzu 1999 RODEO Workshop Manual

6E1–162 RODEO X22SE 2.2L ENGINE DRIVEABILITY AND EMISSION
DIAGNOSTIC TROUBLE CODE (DTC) P0138 O2 SENSOR CIRCUIT HIGH
Circuit Description
To control emissions of hydrocarbons (HC), carbon
monoxide (CO), and oxides of nitrogen (NOx), a
three–way catalytic converter is used. The catalyst within
the converter promotes a chemical reaction which
oxidizes the HC and CO present in the exhaust gas,
converting them into harmless water vapor and carbon
dioxide. The catalyst also reduces NOx, converting it to
nitrogen. The powertrain control module (PCM) has the
ability to monitor this process using the Bank 1 HO2S 1
and the Bank 1 HO2S 2 heated oxygen sensors. The
Bank 1 HO2S 1 sensor produces an output signal which
indicates the amount of oxygen present in the exhaust
gas entering the three–way catalytic converter. The Bank
1 HO2S 2 sensor produces an output signal which
indicates the oxygen storage capacity of the catalyst; this
in turn indicates the catalyst's ability to convert exhaust
gases efficiently. If the catalyst is operating efficiently, the
Bank 1 HO2S 1 signal will be far more active than that
produced by the Bank 1 HO2S 2 sensor. If the Bank 1
HO2S 2 signal voltage remains excessively high for an
extended period of time, Diagnostic Trouble Code P0138
will be set. DTC P0138 is a type A code.
Conditions for Setting the DTC
f No related Diagnostic Trouble Codes.
f Engine is operating in "Closed Loop".
VOLTAGE (BANK 1 SENSOR 2)
f "Closed Loop" commanded air/fuel ratio is between
14.5 and 14.8.
f Engine coolant temperature is above 60°C (140°F).
f Throttle angle is between 3% and 19%.
All above conditions met for 3.0 seconds or in
"Deceleration Fuel Cutoff" DFCO mode, and one
of the following two conditions are met:
f Bank 1 HO2S 2 signal voltage remains above 952 mV
during normal "Closed Loop" operation for a total of
106.25 seconds over a 125–second period of time.
OR
f Bank 1 HO2S 2 signal voltage remains above 474 mV
during deceleration fuel cutoff mode operation for 5
seconds.
Action Taken When the DTC Sets
f The PCM will illuminate the malfunction indicator lamp
(MIL) the first time the fault is detected.
f The PCM will store conditions which were present
when the Diagnostic Trouble Code was set as Freeze
Frame and in the Failure Records data.
Conditions for Clearing the MIL/DTC
f The PCM will turn the MIL OFF on the third consecutive
trip cycle during which the diagnostic has been run and
the fault condition is no longer present.
f A history Diagnostic Trouble Code P0138 will clear
after 40 consecutive warm–up cycles have occurred
without a fault.
D06RX047