Isuzu 1999 RODEO Workshop Manual page 1423

6E2–180
RODEO 6VD1 3.2L ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Trouble Code (DTC) P0138 HO2S Circuit High Voltage Bank 1
Circuit Description
The powertrain control module (PCM) supplies bias
voltage of about 450 mV between the heated oxygen
sensor (HO2S) signal high and signal low circuits. When
measured with a 10 megaohm digital voltmeter, this may
display as low as 320 mV. The oxygen sensor varies the
voltage within a range of about 1000 mV when exhaust is
rich, down through about 10 mV when the exhaust is lean.
The PCM constantly monitors the HO2S signal during
"closed loop" operation and compensates for a rich or
lean condition by decreasing or increasing injector pulse
width as necessary. If the Bank 1 HO2S 2 voltage
remains excessively high for an extended period of time,
DTC P0138 will be set.
Conditions for Setting the DTC
f No related DTCs.
f Engine is operating in "closed loop."
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%.
f Bank 1 HO2S 2 signal voltage remains above 952 mV
during normal "closed loop" operation for a total of 106
seconds over a 125-second period of time.
OR
Sensor 2
f Bank 1 HO2S 2 signal voltage remains above 500 mV
during deceleration fuel cut-off mode operation for up
to 3 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 P0138 will clear after 40 consecutive
warm-up cycles have occurred without a fault.
f DTC P0138 can be cleared by using the Tech 2 "Clear
Info" function or by disconnecting the PCM battery
feed.
Diagnostic Aids
Check for the following conditions:
f Fuel pressure – An excessively rich fuel mixture can
cause a DTC P0138 to be set. Refer to Fuel System
Diagnosis .
f Rich injector(s) – Perform "Injector Balance Test."
f Leaking injector – Refer to Fuel System Diagnosis.
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