1F – 374IENGINE CONTROLS
DAEWOO V–121 BL4
StepNo Yes Value(s) Action
41. Turn the ignition OFF.
2. Disconnect HO2S1 connector.
3. Turn the ignition ON.
Does the scan tool indicate the HO2S1 voltage with-
in the specified value?407–509 mVGo to
”Diagnostic
Aids”Go to Step 5
5Check the HO2S1 signal circuit, terminal 4 for a
short to ground and repair as needed.
Is the repair necessary.–Go to Step 7Go to Step 6
6S Turn the ignition OFF.
S Replace the Engine Control Module (ECM).
Is the repair complete?–Go to Step 7–
71. If disconnected, reconnect HO2S1 connector.
2. Using the scan tool, clear the Diagnostic
Trouble Codes (DTCs).
3. Start the engine and idle at normal operating
temperature.
4. Operate the vehicle within the Conditions for
setting this DTC as specified in the supporting
text.
Does the scan tool indicate that this diagnostic has
run and passed?–Go to Step 8Go to Step 2
8Check if any additional DTCs are set.
Are any DTCs displayed that have not been diag-
nosed?–Go to applica-
ble DTC tableSystem OK
ENGINE CONTROLS 1F – 377
DAEWOO V–121 BL4
StepNo Yes Value(s) Action
41. Turn the ignition OFF.
2. Disconnect HO2S1 connector.
3. Turn the ignition ON.
4. Jumper the Engine Control Module (ECM) side
HO2S1 signal circuit to ground.
Does the scan tool indicate the HO2S1 voltage be-
low the specified value?500 mVGo to
”Diagnostic
Aids”Go to Step 5
5Check the HO2S1 signal circuit, terminal 4 for a
short to voltage and repair as needed.
Is the repair complete?–Go to Step 7Go to Step 6
6S Turn the ignition OFF.
S Replace the ECM.
Is the repair complete?–Go to Step 7–
71. If disconnected, reconnect HO2S1 connector.
2. Using the scan tool, clear the Diagnostic
Trouble Codes (DTCs).
3. Start the engine and idle at normal operating
temperature.
4. Operate the vehicle within the Conditions for
setting this DTC as specified in the supporting
text.
Does the scan tool indicate that this diagnostic has
run and passed?–Go to Step 8Go to Step 2
8Check if any additional DTCs are set.
Are any DTCs displayed that have not been diag-
nosed?–Go to applica-
ble DTC tableSystem OK
ENGINE CONTROLS 1F – 381
DAEWOO V–121 BL4
StepNo Yes Value(s) Action
161. Using the scan tool, clear the Diagnostic
Trouble Codes (DTCs).
2. Start the engine and idle at normal operating
temperature.
3. Operate the vehicle within the Conditions for
setting this DTC as specified in the supporting
text.
Does the scan tool indicate that this diagnostic has
run and passed?–Go to Step 17Go to Step 2
17Check if any additional DTCs are set.
Are any DTCs displayed that have not been diag-
nosed?–Go to
”Applicable
DTC table”System OK
1F – 384IENGINE CONTROLS
DAEWOO V–121 BL4
StepNo Yes Value(s) Action
61. Idle the engine.
2. Remove the jumper wire.
3. Using a voltmeter, measure the voltage be-
tween terminal 4 of HO2S1 and ground
Is the voltage above the specified value?600 mVGo to Step 7Go to Step 11
71. Turn the engine OFF.
2. Using a voltmeter, measure the voltage be-
tween terminal 4 of the HO2S1 and ground.
Is the voltage below the specified value?300 mVGo to Step 9Go to Step 11
8Check the HO2S1 low circuit for an open or short to
ground between terminal 3 of the HO2S1 and termi-
nal M29 of the ECM and repair as needed.
Is the repair complete?–Go to Step 12Go to Step 10
9Check the HO2S1 signal circuit for an open or short
to ground between terminal 4 of the HO2S1 and ter-
minal M12 of the ECM and repair as needed.
Is the repair complete?–Go to Step 12Go to Step 10
10S Turn the ignition OFF.
S Replace the ECM.
Is the repair complete?–Go to Step 12–
11Replace the HO2S1.
Is the repair complete?–Go to Step 12–
121. Using the scan tool, clear the Diagnostic
Trouble Codes (DTCs).
2. Start the engine and idle at normal operating
temperature.
3. Operate the vehicle within the Conditions for
setting this DTC as specified in the supporting
text.
Does the scan tool indicate that this diagnostic has
run and passed?–Go to Step 13Go to Step 2
13Check if any additional DTCs are set.
Are any DTCs displayed that have not been diag-
nosed?–Go to
”Applicable
DTC table”System OK
ENGINE CONTROLS 1F – 387
DAEWOO V–121 BL4
StepNo Yes Value(s) Action
9Check the connections terminal 4 at the HO2S1 con-
nector and repair as necessary.
Is the repair complete?–Go to Step 13Go to Step 12
10Replace the HO2S1 sensor.
Is the action complete?–Go to Step 13–
11Repair the open in the ground circuit.
Is the action complete?–Go to Step 13–
12Repair the open in the ignition feed circuit.
Is the action complete?–Go to Step 13–
131. Using the scan tool, clear the Diagnostic
Trouble Codes (DTCs).
2. Start the engine and idle at normal operating
temperature.
3. Operate the vehicle within the conditions for
setting this DTC as specified in the supporting
text.
Does the scan tool indicate that this diagnostic has
run and passed?–Go to Step 14Go to Step 2
14Check if any additional DTCs are set.
Are any DTCs displayed that have not been diag-
nosed?–Go to
”Applicable
DTC table”System OK
ENGINE CONTROLS 1F – 389
DAEWOO V–121 BL4
S The ECM will record operating conditions at the
time the diagnostic fails. This information will be
stored in the Freeze Frame and Failure Records
buffers.
S A history DTC is stored.
Conditions for Clearing the MIL/DTC
S The MIL will turn off after four consecutive ignition
cycles in which the diagnostic runs without a fault.
S A history DTC will clear after 40 consecutive warm–
up cycles without a fault.
S The DTC(s) can be cleared by using the scan tool.
S Disconnecting the ECM battery feed for more than
10 seconds.
Diagnostic Aids
An intermittent may be caused by rubbed–through wire in-
sulation or a wire contacting the exhaust.
Check for the following conditions:
S Exhaust system – Inspect the exhaust system for
leaks. Check the exhaust between the three–way
catalytic converter and the flange for leaks, corro-
sion, or for loose or missing hardware and repair as
necessary.
S Poor connection or damaged harness – Ensure that
the HO2S2 pigtail is not contacting the exhaust.
Check for the following conditions:
S Improper mating
S Broken locks
S Improperly formedS Damaged terminals
S Poor terminal–to–wire connection
S Damaged harness
S Intermittent test – Observe the HO2S2 on the scan
tool while moving related connections and the wir-
ing harness with the ignition ON. If the failure is in-
duced, the HO2S2 display will change. This may
help isolate the location of the malfunction.
Test Description
Number(s) below refer to the step number(s) on the Diag-
nostic Table.
1. The On–Board Diagnostic (EOBD) System Check
prompts the technician to complete some basic
checks and store the freeze frame and failure re-
cords data on the scan tool if applicable. This
creates an electronic copy of the data taken when
the malfunction occurred. The information is then
stored on the scan tool for later reference.
2. This step determines if DTC P0137 is the result of
a hard failure or an intermittent condition.
4. Jumping the HO2S2 low circuit, terminal 4 to
ground is necessary to allow the ECM to display
the supplied bias voltage. If the voltage is between
0.35 and 0.55 volt, then the wiring and ECM are
OK.
6. The replacement ECM must be reprogrammed.
Refer to the latest Techline procedure for ECM re-
programming.
DTC P0137 – Rear Heated Oxygen Sensor (HO2S2) Low Voltage
StepActionValue(s)YesNo
1Perform an On–Board Diagnostic (EOBD) System
Check.
Was the check performed?–Go to Step 2Go to
”On–Board
Diagnostic Sys-
tem Check”
21. Install a scan tool to the Data Link Connector
(DLC).
2. Turn the ignition ON.
Is the Rear Heated Oxygen Sensor (HO2S2) volt-
age less than the value specified?0.1 VGo to Step 4Go to Step 3
31. Start the engine.
2. Review the Freeze Frame data and note the
parameters.
3. Operate the vehicle within the Freeze frame
conditions and Conditions For Setting the DTC
as noted.
Is the HO2S2 voltage less than the specified value?0.4 VGo to Step 4Go to Step 8
41. Turn the ignition OFF.
2. Disconnect HO2S2 connector.
3. Connect a jumper wire between terminal 1 of
HO2S2 connector and ground.
4. Turn the ignition ON.
Does the scan tool indicate that the HO2S2 voltage
is within the specified value?350–550 mVGo to Step 7Go to Step 5
1F – 390IENGINE CONTROLS
DAEWOO V–121 BL4
StepNo Yes Value(s) Action
51. Turn the ignition OFF.
2. Disconnect the Engine Control Module (ECM)
connector and check the HO2S2 high circuit,
terminal K36 for short to ground or short to the
HO2S2 low circuit terminal M53 and repair as
needed.
Is the repair complete?–Go to Step 8Go to Step 6
6S Turn the ignition OFF.
S Replace the ECM.
Is the repair complete?–Go to Step 8–
7S Turn the ignition OFF.
S Replace the HO2S2.
Is the repair complete?–Go to Step 8–
81. Using the scan tool, clear the Diagnostic
Trouble Codes (DTCs).
2. Start the engine and idle at normal operating
temperature.
3. Operate the vehicle within the Conditions for
setting this DTC as specified in the supporting
text.
Does the scan tool indicate that this diagnostic has
run and passed?–Go to Step 9Go to Step 2
9Check if any additional DTCs are set.
Are any DTCs displayed that have not been diag-
nosed?–Go to
Applicable DTC
tableSystem OK
1F – 392IENGINE CONTROLS
DAEWOO V–121 BL4
Conditions for Clearing the MIL/DTC
S The MIL will turn off after four consecutive ignition
cycles in which the diagnostic runs without a fault.
S A history DTC will clear after 40 consecutive warm–
up cycles without a fault.
S The DTC(s) can be cleared by using the scan tool.
S Disconnecting the ECM battery feed for more than
10 seconds.
Diagnostic Aids
Check for the following conditions:
S Rich exhaust – An overly rich exhaust may load the
catalyst, causing high HO2S2 signal voltages.
S Silicone contamination – A false rich condition may
be caused by silicone contamination of the HO2S2.
This will be indicated by a powdery white deposit on
the sensor.
S Faulty HO2S2 – If HO2S2 is internally shorted, the
HO2S2 voltage displayed on a scan tool will be
over 1 volt. Disconnect the HO2S2 and jumper the
sensor low circuit to engine ground; if the displayed
voltage goes from over 1000 millivolt to around 450
millivolt, replace the HO2S2.S Intermittent test – Observe HO2S2 on the scan tool
while moving related connectors and the wiring har-
ness with the key in the ON position. If the failure is
induced, the HO2S2 display will change. This may
help isolate the location of the malfunction.
Test Description
Number(s) below refer to the step number(s) on the Diag-
nostic Table.
1. The On–Board Diagnostic (EOBD) System Check
prompts the technician to complete some basic
checks and store the freeze frame and failure re-
cords data on the scan tool if applicable. This
creates an electronic copy of the data taken when
the malfunction occurred. The information is then
stored on the scan tool for later reference.
2. This step determines if DTC P0138 is the result of
a hard failure or an intermittent condition.
5. Disconnecting the HO2S2 and jumpering the sen-
sor signal circuit and the sensor low circuit to
ground should cause the scan tool to display
HO2S2 voltage below 100 mv (0.1 v). If the signal
voltage is still high, the ECM is malfunctioning.
6. The replacement ECM must be reprogrammed.
Refer to the latest Techline procedure for ECM re-
programming.
DTC P0138 – Rear Heated Oxygen Sensor (HO2S2) High Voltage
StepActionValue(s)YesNo
1Perform an On–Board Diagnostic (EOBD) System
Check.
Was the check performed?–Go to Step 2Go to
”On–Board
Diagnostic Sys-
tem Check”
21. Install a scan tool to the Data Link Connector
(DLC).
2. Turn the ignition ON.
Is the Rear Heated Oxygen Sensor (HO2S2) volt-
age above the value specified?0.9 VGo to Step 4Go to Step 3
31. Review the Freeze Frame data and note the
parameters.
2. Operate the vehicle within the Freeze frame
conditions and Conditions For Setting the DTC
as noted.
Is the HO2S2 voltage above the specified value?0.9 VGo to Step 4Go to Step 9
41. Turn the ignition OFF.
2. Disconnect HO2S2 connector.
3. Disconnect the Engine Control Module (ECM)
connector.
4. With voltmeter connected to ground, probe the
HO2S2 high signal circuit, terminal K36.
Is the voltage within the specified value?±0 VGo to Step 5Go to Step 6