Isuzu 1999 RODEO Workshop Manual page 865

6E1–238 RODEO X22SE 2.2L ENGINE DRIVEABILITY AND EMISSION
Diagnostic Aids
Due to the moisture associated with exhaust systems, the
EGR valve may freeze and stick in colder weather at
times. After the vehicle is brought into a warm shop for
repairs, the valve warms and the problem disappears. By
watching the Actual EGR and Desired EGR Positions on
a cold vehicle with a Tech 2, the fault can be verified
easily. Check the freeze frame data to determine if the
Diagnostic Trouble Code was set when the vehicle was
cold by viewing the Engine Coolant Temperature (ECT).
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart:
1. The Powertrain OBD System Check prompts the
technician to complete some basic checks and store
the freeze frame and failure records data on the
Tech 2 if applicable. This created an electronic copy
of the data taken when the fault occurred. The
information is then stored on the Tech 2 for later
reference.
2. Commanding the EGR valve open determines
whether the EGR system can control the EGR valve
accurately and if the fault if present.
3. When the EGR valve electrical connector is
disconnected, the Tech 2 should display the Actual
EGR Position as 0%. If is does not, the fault lies
either in the EGR signal circuit or the PCM.
4. A test light, when connected to ground, will glow
dimly when the EGR valve is commanded to 25%,
and brighter as the EGR valve is commanded to
100%. If the test light flashes, check the sensor
ground for an open.
5. An open or poor connection condition may have
caused this Diagnostic Trouble Code to set. Be
sure to check the terminals for being backed out,
improperly formed or damaged, and for poor
tension.
7. The test light will have glowed brightly in the
previous step if the EGR control circuit was shorted
to B+ and the Actual EGR Position on the Tech 2
will display 100%. A test light that did not illuminate,
indicates that the circuit may be open or shorted to
ground.
9. If the EGR valve 5 volt reference is shorted to
voltage, the DVM will read battery voltage and
additional Diagnostic Trouble Codes may be set and
engine performance will be poor.
12. The replacement PCM must be reprogrammed and
the Tooth Error Correction (TEC) procedure must be
performed. Refer to the latest procedures for PCM
reprogramming and Powertrain Control Module for
the Tooth Error Correction (TEC) Procedure.
13. Although the circuitry acted correctly when
checked, a problem may still lie within the terminals
which would not show up in probe type testing. Be
sure to check the terminals for being backed out,
improperly formed or damaged, and for poor
tension.
17. All circuits to the EGR valve are OK at this point.
The fault lies internally in the EGR valve and
therefore must be replaced. Be sure all gasket
material is removed from the EGR mounting
surface. Even a small amount of material may
cause a Diagnostic Trouble Code P0401 to set. For
on vehicle service of the EGR Valve, refer to EGR
Valve.
18. Check the terminals for being backed out,
improperly formed or damaged, and for poor
tension.
19. Clearing the Diagnostic Trouble Codes is a very
important step for this diagnostic. The clearing
function allows the EGR valve to relearn a new
pintle position as the old position was inaccurate
due to the malfunction that caused the Diagnostic
Trouble Code. The Diagnostic Trouble Code must
be cleared with the ignition switch ON, with the
engine OFF or when the engine is idling. If the
PCM sees a EGR command, the new pintle position
will not be learned.