Isuzu 1999 RODEO Workshop Manual page 790

f Diagnostic Trouble Code P0138 can be cleared by
using the Scan Tool's "Clear Info" function.
Diagnostic Aids
Check the following items:
f Fuel pressure – An excessively rich fuel mixture can
cause a Diagnostic Trouble Code 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.
f Evaporative emissions (EVAP) canister purge – Check
for fuel saturation. If full of fuel, check the canister
control and hoses. Refer to Evaporative Emission
(EVAP) Control System.
f Check for a leaking fuel pressure regulator diaphragm
by checking the vacuum line to the regulator for the
presence of fuel.
f TP sensor – An intermittent TP sensor output will
cause the system to go rich, due to a false indication
of the engine accelerating.
f Shorted Heated Oxygen Sensor (HO2S) – If the HO2S
is internally shorted the HO2S voltage displayed on the
Tech 2 will be over 1 volt. Silicon contamination of the
HO2S can also cause a high HO2S voltage. This
condition is indicated by a powdery white deposit on
the portion of the HO2S exposed to the exhaust
stream. If contamination is evident, replace the
affected HO2S.
DTC P0138 – O2 Sensor Circuit High Voltage (Bank 1 Sensor 2)
Step
1 Was the "On–Board Diagnostic (OBD) System Check"
performed?
2 1. Install the Tech 2.
2. Run the engine at operating temperature.
3. Operate the vehicle within parameters specified
under "Conditions for Setting the Diagnostic
Trouble Code" included in Diagnostic Support.
4. Using a Tech 2, monitor Bank 1 HO2S 1 voltage.
Does the Bank 1 HO2S 2 voltage remain above the
specified value?
3 1. Ignition ON review and record Tech 2 Failure
Records data.
2. Operate the vehicle within Failure Records
conditions as noted.
3. Using a Tech 2, monitor "Diagnostic Trouble Code"
info for Diagnostic Trouble Code P0138 until the
Diagnostic Trouble Code P0138 test runs.
4. Note the test result.
Does the Tech 2 indicate Diagnostic Trouble Code
P0138 failed this ignition?
RODEO X22SE 2.2L ENGINE DRIVEABILITY AND EMISSION
Action
f Open HO2S Signal, Low Circuit or Faulty HO2S – A
poor connection or open in the HO2S signal or low
circuit can cause the DTC to set during deceleration
fuel mode. An HO2S which is faulty and not allowing
a full voltage swing between the rich and lean
thresholds can also cause this condition. Operate the
vehicle while monitoring the HO2S voltage with a Tech
2. If the HO2S voltage is limited within a range between
300 mV to 600 mV, check the HO2S signal and low
circuit wiring and associated terminal connections. If
the wiring and connections are OK, replace the HO2S.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart:
3.Diagnostic Trouble Code P0138 being set during
deceleration fuel mode operation may indicate a
condition described in the "Diagnostic Aids" above.
If the Diagnostic Trouble Code P0138 test passes
while the Failure Records conditions are being
duplicated, an intermittent condition is indicated.
Reviewing the Failure Records vehicle mileage
since the diagnostic test last failed may help
determine how often the condition that caused the
Diagnostic Trouble Code to be set occurs. This may
assist in diagnosing the condition.
Value(s)
— Go to Step 2
952 mV Go to Step 4
— Go to Step 4
6E1–163
Yes No
Go to OBD
System
Check
Go to Step 3
Refer to
Diagnostic
Aids