Isuzu engine C22NE / 22LE / 20LE. Service manual — part 60

DRIVEABILITY AND EMISSIONS 6E1-69

Diagnostic Aids

Important: Be sure to inspect ECM and engine

grounds for being secure and clean.

A short to voltage in one of the sensor input circuits

may cause one or more of the following DTCs to be

set:
• 21/33
Important: If a sensor input circuit has been shorted

to voltage, ensure that the sensor is not damaged. A

damaged sensor will continue to indicate a high or low

voltage after the affected circuit has been repaired. If

the sensor has been damaged, replace it.

A short to ground in the circuit between ECM and

sensors will cause one or more of the following DTCs

to be set:
• 14/22
• 34/69

Check for the following conditions:
• Poor connection at ECM. Inspect the harness

connectors for backed-out terminals, improper

mating, broken locks, improperly formed or

damaged terminals, and a poor terminal-to-wire

connection.

• Damaged harness. Inspect the wiring harness for

damage. If the harness is not damaged, observe an

affected sensor's displayed value on the Scan Tool

with the ignition ON and the engine OFF while you

move the connectors and the wiring harnesses

related to the following sensors:

• IAT
• ECT
• TPS
• MAP

Multiple ECM Information Sensor DTCs Set

Step

Action

Value(s)

Yes

No

1

Was the “On-Board Diagnostic (OBD) System

Check” performed?

-

Go to Step 2

Go to OBD

System

Check

2

1. Turn the ignition OFF disconnect the ECM.

2. Turn the ignition ON check the 5 volt reference circuits

for the following conditions:
• A poor connection at the ECM.
• An open between the ECM connector and the splice.
• A short to ground.
• A short to voltage.

Is there an open or short?

-

Go to Step 3

Go to Step 4

3

Repair the open or short.

Is the action complete?

-

Verify repair

-

4

Check the sensor ground circuit for the following

conditions:
• A poor connection at the ECM or the affected sensors.
• An open between the ECM connector and the affected

sensors.

Is there an open or a poor connection?

-

Go to Step 5

Go to Step 6

5

Repair the open or the poor connection.

Is the action complete?

-

Verify repair

-

6E1-70 DRIVEABILITY AND EMISSIONS

Multiple ECM Information Sensor DTCs Set (Cont'd)

Step

Action

Value(s)

Yes

No

6

Measure the voltage between the MAP sensor signal

circuit at the ECM harness connector and ground.

Does the voltage measure near the specified value?

0V

Go to Step 7

Go to Step 10

7

Measure the voltage between the TP sensor signal circuit

at the ECM harness connector and ground.

Does the voltage measure near the specified value?

0V

Go to Step 8

Go to Step 11

8

Measure the voltage between the IAT sensor signal circuit

at the ECM harness connector and ground.

Does the voltage measure near the specified value?

0V

Go to Step 9

Go to Step 12

9

Measure the voltage between the ECT sensor signal

circuit at the ECM harness connector and ground.

Does the voltage measure near the specified value?

0V

Go to Step 14

Go to Step 13

10

Locate and repair the short to voltage in the MAP sensor

signal circuit.

Is the action complete?

-

Verify repair

-

11

Locate and repair the short to voltage in the TP sensor

signal circuit.

Is the action complete?

-

Verify repair

-

12

Locate and repair the short to voltage in the IAT sensor

signal circuit.

Is the action complete?

-

Verify repair

-

13

Locate and repair the short to voltage in the ECT sensor

signal circuit.

Is the action complete?

-

Verify repair

-

14

Replace the EPPROM or ECM.

Note) Refer to 6E1-243

-

Go to OBD

System

Check

-

DRIVEABILITY AND EMISSIONS 6E1-71

ENGINE SCAN TOOL DATA

DEFINITIONS AND RANGES

A/C CLUTCH - Scan Tool Displays ON or OFF -

Indicates whether the ECM has commanded the A/C

clutch ON. Used in A/C system diagnostics.

A/C REQUEST - Scan Tool Displays NO or OFF -

Indicates the state of the A/C request input circuit from

the HVAC controls. The ECM uses the A/C request

signal to determine whether A/C compressor operation

is being requested.

AIR/FUEL RATIO - Scan Tool Range 0-0:1-25.5:1 -

Air/fuel ratio indicates the ECM commanded value. In

“Closed Loop” , the air/fuel ratio should normally be

displayed around “14.2-14.7” . A lower air/fuel ratio

indicates a richer commanded mixture, which may be

seen during power enrichment or TWC (If applicable)

protection modes. A higher air/fuel ratio indicates a

leaner commanded mixture. This can be seen during

deceleration fuel mode.

BARO kPa - Scan Tool Range 10-105 - The

barometric pressure reading is determined from the

MAP sensor signal monitored during key up and wide

open throttle (WOT) conditions. The barometric

pressure is used to compensate for altitude

differences and is normally displayed around “61-104”

depending on altitude and barometric pressure.

DECELERATION FUEL CUT OFF - YES or NO-

Scan Tool Displays - “ACTIVE” displayed indicates

that the ECM has detected conditions appropriate to

operate in deceleration fuel mode. The ECM will

command the deceleration fuel mode when it detects

a closed throttle position while the vehicle is traveling

over 20 mph. While in the deceleration fuel mode, the

ECM will decrease the amount of fuel delivered by

entering “Open Loop” and decreasing the injector

pulse width.

DESIRED IDLE - Scan Tool Range 0-3187 RPM -

The idle speed that the ECM is commanding. The

ECM will compensate for various engine loads based

on engine coolant temperature, to keep the engine at

the desired speed.

ECT TEMP. - (Engine Coolant Temperature) Scan

Tool Range

−−−−40°C to 151°C (−−−−40°F to 304°F) - The

engine coolant temperature (ECT) is mounted in the

coolant stream and sends engine temperature

information to the ECM. The ECM applies 5 volts to

the ECT sensor circuit. The sensor is a thermistor

which changes internal resistance as the temperature

changes. When the sensor is cold (high resistance),

the ECM monitors a high signal voltage and interprets

that as a cold engine. As the sensor warms

(decreasing resistance), the voltage signal will

decrease and the ECM will interpret the lower voltage

as a warm engine.

TIME FROM START - Scan Tool Range 00:00:00-

99:99:99 Hrs:Min:Sec - Indicates the time elapsed

since the engine was started. If the engine is stopped,

engine run time will be reset to 00:00:00.

ENGINE SPEED - Range 0-9999 RPM - Engine

speed is computed by the ECM form the 58X

reference input. It should remain close to desired idle

under various engine loads with engine idling.

EVAP PURGE PWM (If applicable) - Scan Tool

Range 0%-100% - Represents the ECM commanded

PWM duty cycle of the EVAP purge solenoid valve.

“0%” displayed indicates no purge; “100%” displayed

indicates full purge.

FUEL PUMP RELAY - Scan Tool Displays ON or

OFF - Indicates the ECM commanded state of the fuel

pump relay driver circuit.

02 BLM CELL NUMBER (If applicable)- Scan Tool

Range 0-21 - The 02 BLM cell is dependent upon

engine speed and MAP sensor readings. A plot of

RPM vs. MAP is divided into 22 cells. 02 BLM cell

indicates which cell is currently active.

B1 HO2S BANK 1 (If applicable)- Scan Tool Range

0-1000 mV - Represents the fuel control exhaust

oxygen sensor output voltage. Should fluctuate

constantly within a range between 10 mV (lean

exhaust) and 1000 mV (rich exhaust) while operating

in “Closed Loop” .

B1 HO2S READY BANK 1 (If applicable)- Scan Tool

Displays YES or NO - Indicates the status of the

exhaust oxygen sensor. The Scan Tool will indicate

that the exhaust oxygen sensor is ready when the

ECM detects a fluctuating HO2S voltage sufficient to

allow “Closed Loop” operation. This will not occur

unless the exhaust sensor is warmed up.

IAC CONTROL STEP - Scan Tool Range 0-255

steps - Displays the commanded position of the idle

air control pintle in counts. A larger number of counts

means that more air is being commanded through the

idle air passage. Idle air control should respond fairly

quickly to changes in engine load to maintain desired

idle RPM.

IAT (INTAKE AIR TEMPERATURE) - Scan Tool

Range

−−−−40°C to 151°C (−−−−40°F to 304°F) - The ECM

converts the resistance of the intake air temperature

sensor to degrees. Intake air temperature (IAT) is

6E1-72 DRIVEABILITY AND EMISSIONS

used by the ECM to adjust fuel delivery and spark

timing according to incoming air density.

BATTERY - Scan Tool Range 0-25.5 Volts - This

represents the system voltage measured by the ECM

at its ignition feed.

INJ. PULSE WIDTH - Scan Tool Range 0-1000

msec. - Indicates the amount of time the ECM is

commanding each injector ON during each engine

cycle. A longer injector pulse width will cause more

fuel to be delivered. Injector pulse width should

increase with increased engine load.

FUELING MODE (If applicable) - Scan Tool

Displays OPEN or CLOSED - “CLOSED” indicates

that the ECM is controlling fuel delivery according to

oxygen sensor voltage. In “OPEN” the ECM ignores

the oxygen sensor voltage and bases the amount of

fuel to be delivered on TP sensor, and engine coolant,

sensor inputs only.

MAP - Scan Tool Range 10-105 kPa (0.00-4.97

Volts) - The manifold absolute pressure (MAP) sensor

measures the change in the intake manifold pressure

from engine load, and speed changes. As intake

manifold pressure increases, intake vacuum

decreases, resulting in a higher MAP sensor voltage

and kPa reading. The MAP sensor signal is used to

monitor intake manifold pressure changes to update

the BARO reading, and as an enabling factor for

several of the diagnostics.

CEL-CHECK ENGINE LIGHT - Scan Tool Displays

ON or OFF - Indicates the ECM commanded state of

the malfunction indicator lamp (“Check Engine

Lamp”).

02 STATUS (If applicable) - Scan Tool Displays

RICH or LEAN - Indicates whether oxygen sensor

voltage is above a 600 mV threshold voltage (“RICH” )

or below a 3000 mV threshold voltage (“LEAN” ).

Should change constantly while in “Closed Loop” ,

indicating that the ECM is controlling the air/fuel

mixture properly.

ELECTRIC SPARK CONTROL - Scan Tool Range

−−−−

64°CA to 64°CA - Displays the amount of spark

advance being commanded by the ECM on the IC

circuit.

THROTTLE POSITION - Scan Tool Range 0%-100%

- TP (throttle position) angle is computed by the ECM

from the TP sensor voltage. TP angle should display

“0%” at idle and “100%” at wide open throttle.

TPS SIGNAL - Scan Tool Range 0.00-5.00 Volts -

The voltage being monitored by the ECM on the TP

sensor signal circuit.

TYPICAL SCAN DATA VALUES

Use the Typical Scan Data Values Table only after the

On- Board Diagnostic System Check has been

completed, no DTC(s) were noted, and you have

determined that the on-board diagnostics are

functioning properly. Scan Tool values from a

properly-running engine may be used for comparison

with the engine you are diagnosing. The typical scan

data values represent values that would be seen on a

normally-running engine.

Notice: A Scan Tool that displays faulty data should

not be used, and the problem should be reported to

the Scan Tool manufacturer. Use of a faulty Scan Tool

can result in misdiagnosis and unnecessary

replacement of parts.

Only the parameters listed below are referred to in this

manual for use in diagnosis. For further

information on using the Scan Tool to diagnose the

ECM and related sensors, refer to the applicable

reference section listed below. If all values are within

the typical range described below, refer to the

Symptoms section for diagnosis.

Test Conditions

Engine running, lower radiator hose hot, transmission

in park or neutral, “Closed Loop” (If applicable),

accessories OFF, brake not applied and air

conditioning OFF.