Isuzu 1999 RODEO Workshop Manual page 1448

Diagnostic Trouble Code (DTC) P0157 HO2S Circuit Low Voltage Bank 2
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 2 HO2S 1
and the Bank 2 HO2S 2 heated oxygen sensors. The
Bank 2 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
2 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 2 HO2S 1 signal will be far more active than that
produced by the Bank 2 HO2S 2 sensor. If the Bank 2
HO2S 2 signal voltage remains excessively low for an
extended period of time, DTC P0157 will be set.
Conditions for Setting the DTC
f No related DTCs.
f The engine is operating in "closed loop."
f Engine coolant temperature is above 60°C (140°F).
RODEO 6VD1 3.2L ENGINE DRIVEABILITY AND EMISSIONS
Sensor 2
f "Closed loop" commanded air/fuel ratio is between
14.5 and 14.8
f Throttle angle is between 3% and 19%.
f Bank 2 HO2S 2 signal voltage remains below 22 mV
during normal "closed loop" operation for a total of 106
seconds over a 125-second period of time.
OR
f Bank 2 HO2S 2 signal voltage remains below 400 mV
during "power enrichment" mode fuel control operation
for up to 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 DTC 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 DTC P0157 will clear after 40 consecutive
warm-up cycles have occurred without a fault.
f DTC P0157 can be cleared by using the Tech 2 "Clear
Info" function or by disconnecting the PCM battery
feed.
6E2–205
D06RW065