P0131 Ho2S Circuit Low Voltage Bank 1 Sensor 1 - Isuzu 2000 Trooper Workshop Manual

P0131 HO2S Circuit Low Voltage Bank 1 Sensor 1

Circuit Description
The powertrain control module (PCM) supplies a 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 350 mV. The oxygen sensor varies the
voltage within a range of about 1000 mV when the
exhaust is rich, down through about 10 mV when 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 1 voltage
remains excessively low for an extended period of time,
DTC P0131 will be set.
Conditions for Setting the DTC
D No related DTCs.
D Vehicle is operating in "closed loop."
D Engine coolant temperature is above 60°C (140°F).
D "Closed loop" commanded air/fuel ratio is between
14.5 and 14.8.
D Throttle angle is between 3% and 19%.
D Bank 1 HO2S 1 signal voltage remains below 22 mV
during normal "closed loop" operation for a total of 77
seconds over a 90-second period of time.
TROOPER 6VE1 3.5L ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Trouble Code (DTC)
Action Taken When the DTC Sets
D The PCM will illuminate the malfunction indicator lamp
(MIL) the first time the fault is detected.
D The PCM will store conditions which were present
when the DTC was set as Freeze Frame and in the
Failure Records data.
D "Open loop" fuel control will be in effect.
Conditions for Clearing the MIL/DTC
D 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.
D A history DTC P0131 will clear after 40 consecutive
warm-up cycles have occurred without a fault.
D DTC P0131 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:
D Heated oxygen sensor wiring – The sensor pigtail may
be routed incorrectly and contacting the exhaust
system.
D Poor PCM to engine block grounds.
D Fuel pressure – The system will go lean if pressure is
too low. The PCM can compensate for some
decrease. However, If fuel pressure is too low, a DTC
P0131 may be set. Refer to Fuel System Diagnosis .
D Lean injector(s) – Perform "Injector Balance Test."
6E–169
D06RY00170