Content .. 61 62 63 64 ..

Isuzu engine C22NE / 22LE / 20LE. Manual - part 63

DRIVEABILITY AND EMISSIONS 6E1-81

SYMPTOM DIAGNOSIS

PRELIMINARY CHECKS

Before using this section, perform the "On-Board

Diagnostic (OBD) System Check" and verify all of the

following items:
• The engine control module (ECM) and malfunction

indicator lamp (MIL) (Check Engine lamp) are

operating correctly.

• There are no Diagnostic Trouble Code(s) stored.
• Scan Tool data is within normal operating range.

Refer to Typical Scan Data Values.

• Verify the customer complaint and locate the

correct symptom in the table of contents. Perform

the procedure included in the symptom chart.

VISUAL/PHYSICAL CHECK

Several of the symptom procedures call for a careful

visual/physical check. This can lead to correcting a

problem without further checks and can save valuable

time. This check should include the following items:
• ECM grounds for cleanliness, tightness and proper

location.

• Vacuum hoses for splits, kinks, and proper

connections, shown on the " Emission Control

System Schematics". Check thoroughly for any type

of leak or restriction.

• Air intake ducts for collapsed or damaged areas.
• Air leaks at throttle body mounting area, manifold

absolute pressure (MAP) sensor and intake

manifold sealing surfaces.

• Ignition wires for cracking, hardness, and carbon

tracking.

• Wiring for proper connections, pinches and cuts.

INTERMITTENT

Important: An intermittent problem may or may not

turn on the malfunction indicator lamp (MIL) or store a

Diagnostic Trouble Code. DO NOT use the Diagnostic

Trouble Code (Diagnostic Trouble Code) charts for

intermittent problems. The fault must be present to

locate the problem.

Most intermittent problems are caused by faulty

electrical connections or wiring. Perform a careful

visual/physical check for the following conditions.

• Poor mating of the connector halves or a terminal

not fully seated in the connector (backed out).

• Improperly formed or damaged terminal.
• All connector terminals in the problem circuit should

be carefully checked for proper contact tension.

• Poor terminal-to-wire connection. This requires

removing the terminal from the connector body to

check.

• Ignition coil shorted to ground and arcing at ignition

wires or plugs.

• MIL (Check Engine lamp) wire to ECM shorted to

ground.

• Poor ECM grounds. Refer to the ECM wiring

diagrams.

Road test the vehicle with a 5-8840-2392-0 Digital

Multimeter connected to a suspected circuit. An

abnormal voltage when the malfunction occurs is a

good indication that there is a fault in the circuit being

monitored.

Use a Scan Tool to help detect intermittent conditions.

The Scan Tools have several features that can be

used to locate an intermittent condition. Use the

following features to find intermittent faults:

To check for loss of diagnostic code memory,

disconnect the MAP sensor and idle the engine until

the MIL (Check Engine lamp) comes on. Diagnostic

Trouble Code 34 should be stored and kept in memory

when the ignition is turned "OFF." If not, the ECM is

faulty. When this test is completed, make sure that

you clear the Diagnostic Trouble Code 34 from

memory.

Check for improper installation of electrical options

such as lights, cellular phones, etc. Check all wires

from the ECM to the ignition control module for poor

connections.

Check for an open diode across the A/C compressor

clutch and check for other open diodes (refer to wiring

diagrams in Electrical Diagnosis).

If problem has not been found, refer to ECM

Connector Symptom tables.

6E1-82 DRIVEABILITY AND EMISSIONS

Hard Start Symptom

Step

Action

Value(s)

Yes

DEFINITION: Engine cranks, but does not start for a long time. Does eventually run, or may start but immediately

stalls.

Was the On-Board Diagnostic (OBD) System Check

performed?

Go to Step 2

Go to OBD

System

Check

1. Perform a bulletin search.

2. If a bulletin that addresses the symptom is found,

correct the condition as instructed in the bulletin.

Was a bulletin found that addresses the symptom?

Verify Repair

Go to Step 3

Was a visual/physical check performed?

Go to Step 4

Go to

Visual/Physic

al Check

Check engine coolant temperature (ECT) sensor for shift

in value.

1. After 8 hours with the hood up and the engine not

running, connect the Scan Tool.

2. Ignition ON, engine not running.

3. Using the Scan Tool, compare Engine Coolant

Temperature to Intake Air Temperature.

Are ECT and IAT within the specified value of each other?

±5°C

(

±9°F)

Go to Step 8

Go to Step 5

1. Using a Scan Tool, display the engine coolant

temperature and note the value.

2. Check the resistance of the engine coolant

temperature sensor.

3. Refer to Temperature vs. Resistance chart in

Diagnostic Trouble Code 14 for resistance

specifications.

Is the actual resistance near the resistance value in the

chart for the temperature that was noted?

Go to Step 7

Go to Step 6

Replace the ECT sensor.

Is the action complete?

Verify repair

Located and repair high resistance or connection in the

ECT signal circuit or the ECT signal circuit or the ECM

sensor ground.

Verify repair

Check for a faulty, plugged, or incorrectly installed PCV

hoses.

Was a problem found?

Verify repair

Go to Step 9

Visually/Physically inspect the secondary ignition wires.

Check for the following conditions:
• Verify that all ignition wire resistance are less than the

specified value.

• Verify that ignition wires are correctly routed to eliminate

cross-firing.

• Verify that ignition wires are not arcing to ground.
Spraying the secondary ignition wires with a light mist of

water may help locate an intermittent problem.

Was a problem found?

#1 cyl. 4.7k

Ω

#2 cyl. 3.9k

Ω

#3 cyl. 3.4k

Ω

#4 cyl. 3.1k

Ω

Verify repair

Go to Step 10

DRIVEABILITY AND EMISSIONS 6E1-83

Hard Start Symptom (Cont'd)

Step

Action

Value(s)

Yes

Check for proper ignition voltage output with a spark tester

(Use commercially available tool).

Was a problem found?

Verify repair

Go to Step 11

1. Remove the spark plugs and check for gas or oil

fouling cracks, wear, improper gap, burned electrodes,

heavy deposits, or improper heat range.

If spark plugs are fouled, the cause of fouling must be

determined before replacing the spark plugs.

Was a problem found?

Verify repair

Go to Step 12

Check for a loose ignition control module ground.

Was a problem found?

Verify repair

Go to Step 13

1. Check the ignition coil secondary resistance.

2. Replace the coil if it is greater than the specified

resistance.

Did the coil require replacement?

2.5 k

Ω

Verify repair

Go to Step 14

Check IAC operation. Perform the procedure in the

diagnostic chart Diagnostic Trouble Code 35, Step 6.

Was a problem found?

Verify repair

Go to Step 15

Check for water or alcohol contaminated fuel.

Was a problem found?

Verify repair

Go to Step 16

Perform the procedure in Fuel System Pressure Test to

determine if there is a problem with fuel delivery.

Was a problem found?

Verify repair

Go to Step 17

Check for the following engine mechanical problems (refer

to Engine Mechanical):
• Low compression
• Leaking cylinder head gaskets
• Worn camshaft
• Camshaft drive belt slipped or stripped
Was a problem found?

Verify repair

Go to Step 18

1. Review all diagnostic procedures within this table.

2. If all procedures have been completed and no

malfunctions have been found, review/inspect the

following:
• Visual/physical inspection
• Scan Tool data
• All electrical connections within a suspected circuit

and/or system

Was a problem found?

Verify repair

Contact

Technical

Assistance

6E1-84 DRIVEABILITY AND EMISSIONS

Surges and/or Chuggles Symptom

Step

Action

Value(s)

Yes

DEFINITION: Engine power variation under steady throttle or cruise. Feels like the vehicle speeds up and slows

down with no change in the accelerator pedal.

Was the On-Board Diagnostic (OBD) System Check

performed?

Go to Step 2

Go to OBD

System

Check

1. Perform a bulletin search.

2. If a bulletin that addresses the symptom is found,

correct the condition as instructed in the bulletin.

Was a bulletin found that addresses the symptom?

Verify Repair

Go to Step 3

Was a visual/physical check performed?

Go to Step 4

Go to Visual/

Physical

Check

Be sure that the driver understands A/C compressor

operation as explained in the owner's manual.

Inform the customer how the A/C clutch operate.

Is the customer experiencing a normal condition?

System OK

Go to Step 5

Check the fuel control Heated Oxygen Sensor (HO2S) (If

applicable). When monitored on the Scan Tool, the HO2S

should respond quickly to different throttle positions. If it

doesn't check for silicon or other contaminants from fuel or

use of improper RTV sealant. The sensors may have a

white powdery coating. Silicon contamination sends a rich

exhaust signal which causes the ECM to command an

excessively lean air/fuel mixture.

Was a problem found?

Verify repair

Go to Step 6

Check the fuel pressure. Refer to Fuel System Pressure

Test.

Was a problem found?

Verify repair

Go to Step 7

Monitor "02 Status" on the Scan Tool (If applicable).

Is "02 Status" in the (rich condition)?

Go to Step 8

Go to Step 9

Check items that can cause the engine to run rich.

Refer to Diagnostic Aids in Diagnostic Trouble Code 45 (If

applicable).

Was a problem found?

Verify repair

Go to Step 10

Check items that can cause the engine to run lean.

Refer to Diagnostic Aids in Diagnostic Trouble Code 44 (If

applicable).

Was a problem found?

Verify repair

Go to Step 10

Check for proper ignition voltage output with the spark

tester (Use commercially available tool).

Was a problem found?

Verify repair

Go to Step 11

Check for a loose ignition control module ground.

Was a problem found?

Verify repair

Go to Step 12

Content .. 61 62 63 64 ..