Isuzu engine C22NE / 22LE / 20LE. Manual - part 53

DRIVEABILITY AND EMISSIONS  6E1-41

Engine Component Locator Table

Number

Name

Location

1

Engine Coolant Temperature (ECT) Sensor

Front of engine, next to the thermostat housing

2

Heated Oxygen Sensor (HO2S)

On the exhaust pipe, left side of engine,

immediately behind the exhaust manifold

3

Air Cleaner

Left front the engine bay

4

Intake Air Temperature (IAT) Sensor

On the intake air duct near the air cleaner

5

Positive Crankcase Ventilation (PCV) Port

On the right front corner of the valve cover

6

Fuel Pressure Regulator

On the rear end of the fuel rail

7

Throttle Body

Between the intake air duct and the intake

manifold

8

Fuse/Relay Box

Along the inside of the right fender

9

Throttle Position (TP) Sensor

On the front of the throttle body

10

Idle Air Control (IAC) Valve

Under the TP sensor

11

EVAP Canister Purge Control Solenoid

On the intake manifold

12

Ignition Coil

Above the starter motor

13

Manifold Absolute Pressure (MAP) Sensor

Bolted to the front edge of the intake

manifold, under the fuel rail

*14

EVAP Canister

On the left side Tire house

*15

Check and Relief valve

On the canister hold brace

* If applicable

Undercarriage Component Locator Table

Name

Location

Fuel Pump Assembly

Installed in the top of the fuel tank

EVAP Purge Control Solenoid Valve

At the right rear of the engine

Vehicle Speed Sensor (VSS)

Protrudes from the right side of the transmission

housing, rear the output shaft

Crankshaft Position (CKP) Sensor

Lower left hand front of engine, behind power steering

pump bracket

6E1-42  DRIVEABILITY AND EMISSIONS

UNDERHOOD (U/H) FUSE AND RELAY PANEL

INSTRUMENT PANEL (I/P) FUSE BLOCK

DRIVEABILITY AND EMISSIONS  6E1-43

DIAGNOSIS

STRATEGY-BASED

DIAGNOSTICS

STRATEGY-BASED DIAGNOSTICS

The strategy-based diagnostic is a uniform approach

to repair all Electrical/Electronic (E/E) systems. The

diagnostic flow can always be used to resolve an E/E

system problem and is a starting point when repairs

are necessary. The following steps will instruct the

technician how to proceed with a diagnosis:

1. Verify the customer complaint.

• To verify the customer complaint, the technician

should know the normal operation of the system.

2. Perform preliminary checks.

• Conduct a thorough visual inspection.
• Review the service history.
• Detect unusual sounds or odors.
• Gather diagnostic trouble code information to

achieve an effective repair.

3. Check bulletins and other service information.

• This includes videos, newsletters, etc.

4. Refer to service info (manual) system check(s).

• “System checks” contain information on a

system that may not be supported by one or

more DTCs. System checks verify proper

operation of the system. This will lead the

technician in an organized approach to

diagnostics.

5.  Refer to service diagnostics.

DTC STORED

Follow the designated DTC chart exactly to make an

effective repair.

NO DTC

Select the symptom from the symptom tables. Follow

the diagnostic paths or suggestions to complete the

repair. You may refer to the applicable

component/system check in the system checks.

NO MATCHING SYMPTOM

1.  Analyze the complaint.

2.  Develop a plat for diagnostics.

3. Utilize the wiring diagrams and the theory of

operation.

Call technical assistance for similar cases where

repair history may be available. Combine technician

knowledge with efficient use of the available service

information.

INTERMITTENTS

Conditions that are not always present are called

intermittents. To resolve intermittents, perform the

following steps:

1. Observe DTCs and DTC modes

2. Evaluate the symptoms and the conditions

described by the customer.

3. Use a check sheet or other method to identify the

circuit or electrical system component.

4. Follow the suggestions for intermittent diagnosis

found in the service documentation.

Most Scan Tools, such as the Tech 2 and the 5-8840-

2392-0, have data-capturing capabilities that can

assist in detecting intermittents.

NO TROUBLE FOUND

This condition exists when the vehicle is found to

operate normally. The condition described by the

customer may be normal. Verify the customer

complaint against another vehicle that is operating

normally. The condition may be intermittent. Verify the

complaint under the conditions described by the

customer before releasing the vehicle.

1.  Re-examine the complaint.

When the complaint cannot be successfully found

or isolated, a re-evaluation is necessary. The

complaint should be re-verified and could be

intermittent as defined in Intermittents, or could be

normal.

2.  Repair and verify.

After isolating the cause, the repairs should be

made. Validate for proper operation and verify that

the symptom has been corrected. This may involve

road testing or other methods to verify that the

complaint has been resolved under the following

conditions:
• Conditions noted by the customer.
• If a DTC was diagnosed, verify a repair by

duplicating conditions present when the DTC

was set as noted in the customer complaint.

6E1-44  DRIVEABILITY AND EMISSIONS

VERIFYING VEHICLE REPAIR

Verification of the vehicle repair will be more

comprehensive for vehicles with OBD system

diagnostics. Following a repair, the technician should

perform the following steps:

Important: Follow the steps below when you verify

repairs on OBD systems. Failure to follow these steps

could result in unnecessary repairs.

1.  Review and record the customer complaint for the

DTC which has been diagnosed.

2.  Clear the DTC(s).

3. Operate the vehicle within conditions noted in the

customer complaint.

4. Monitor the DTC status information for the specific

DTC which has been diagnosed until the diagnostic

test associated with that DTC runs.

GENERAL SERVICE

INFORMATION

OBD SERVICEABILITY ISSUES

Fuel Quality

Fuel quality is not a new issue for the automotive

industry. The Reed Vapor Pressure of the fuel can

also create problems in the fuel system, especially

during the spring and fall months when severe

ambient temperature swings occur. A high Reed

Vapor Pressure could show up as a rich DTC due to

excessive canister loading. High vapor pressures

generated in the fuel tank can also affect the

Evaporative Emission diagnostic as well.

Using fuel with the wrong octane rating for your

vehicle may cause driveability problems. Many of the

major fuel companies advertise that using “premium”

gasoline will improve the performance of your vehicle.

Most premium fuels use alcohol to increase the

octane rating of the fuel. Although alcohol-enhanced

fuels may raise the octane rating, the fuel's ability to

turn into vapor in cold temperatures deteriorates. This

may affect the starting ability and cold driveability of

the engine.

Low fuel levels can lead to fuel starvation, lean engine

operation, and eventually engine misfire.

Non-OEM Parts

All of the OBD diagnostics have been calibrated to run

with OEM parts. Small leaks in the exhaust system

near the heated oxygen sensor can also cause the

MIL (“Check Engine“ lamp) to turn on.

Aftermarket electronics, such as cellular phones,

stereos, and anti-theft devices, may radiate EMI into

the control system if they are improperly installed. This

may cause a false sensor reading and turn on the MIL

(“Check Engine” lamp).

Poor Vehicle Maintenance

The sensitivity of OBD diagnostics will cause the MIL

(“Check Engine” lamp) to turn ON if the vehicle is not

maintained properly. Restricted air filters, fuel filters,

and crankcase deposits due to lack of oil changes or

improper oil viscosity can trigger actual vehicle faults.

Poor vehicle maintenance can not be classified as a

“non-vehicle fault” , but with the sensitivity of OBD

diagnostics, vehicle maintenance schedules must be

more closely followed.

Related System Faults

Many of the OBD system diagnostics will not run if the

ECM detects a fault on a related system or

component. One example would be that if the ECM

detected a Evap. Purge Solenoid fault, The diagnosis

on the Oxygen Sensor (If applicable) would be

suspended until the Evap. Purge Solenoid repaired. If

this happened, the customer may have to make two

trips to the dealership in order to repair the vehicle.

MAINTENANCE SCHEDULE

Refer to the Maintenance Schedule.

VISUAL/PHYSICAL ENGINE

COMPARTMENT INSPECTION

Perform a careful visual and physical engine

compartment inspection when performing any

diagnostic procedure or diagnosing the cause of an

emission test failure. This can often lead to repairing a

problem without further steps. Use the following

guidelines when performing a visual/thysical

inspection:
• Inspect all vacuum hoses for punches, cuts,

disconnects, and correct routing.

• Inspect hoses that are difficult to see behind other

components.

• Inspect all wires in the engine compartment for

proper connections, burned or chafed spots,

pinched wires, contact with sharp edges or contact

with hot exhaust manifolds or pipes.