1F–98 ENGINE CONTROLS
DAEWOO M-150 BL2
MAA1F140
DIAGNOSTIC TROUBLE CODE (DTC) – P0138 HEATED OXYGEN SENSOR HIGH
VOLTAGE
Circuit Description
The engine control module (ECM) supplies a voltage of
about 450mm volts between the ECM terminals 64 and
13. The Heated oxygen (O2) sensor varies the voltage
within a range of about 1volt if the exhaust is rich, down
to about 100mm volts if the exhaust is lean. The Heated
O2 sensor is like an open circuit and produces no volt-
age when it is below 360°C(600°F). An open O2 sensor
circuit or a cold O2 sensor causes “open loop” operation.
Conditions for Setting the DTC
D The Heated oxygen sensor voltage is more than 4.8V
for at least 0.2 seconds.
D A high voltage condition exists.
Action Taken when the DTC Sets
D Emission related.
D “Armed” after two trip with a fail.
D “Disarmed” after one trip with a pass.
D MIL on if failure is detected in three consecutive trips.
D Stores a History DTC on the third consecutive with a
fail (The DTC will be armed after the second fail).
D Stores a Freeze Frame on the third consecutive trip
with a fail (if empty).
Conditions for Clearing the MIL/DTC
D The MIL will turn off after four consecutive ignition
cycles in which the diagnostic runs without a fault.
D A history DTC will clear after 40 consecutive warm up
cycles without a fault.
D DTC(s) can be cleared by using the scan tool.
Diagnostic Aids
D Normal scan tool voltage varies between 0.1volts and
0.9volts while in closed loop.
D Inspect the oxygen (O2) sensor wire. The O2 sensor
may be positioned incorrectly and contacting the ex-
haust manifold.
D Check for an intermittent ground in the wire between
the O2 sensor and the engine control module.
D Perform an injector 2alance test to determine if a re-
stricted fuel injector may be causing the lean condi-
tion.
D Vacuum of crankcase leaks will cause a lean running
condition.
D An exhaust manifold gasket leak of a cracked ex-
haust manifold may cause outside air to be pulled into
the exhaust and past the sensor.
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