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Isuzu engine C22NE / 22LE / 20LE. Service manual - part 98

DRIVEABILITY AND EMISSIONS 6E1-221

Engine

Control

Module

(ECM)

A/C

Compressor

Relay

Control

A16

B10

Thermo

Switch

Pressure

Switch

0.5G/W

A/C Switch

0.5

G/Y

0.5

GR/Y

0.5

G/R

0.5

G/B

DIAGNOSTIC TROUBLE CODE (DTC) (Flash DTC = 88)

A/C COMPRESSOR CLUTCH RELAY HIGH ERROR

Circuit Description

The engine control module (ECM) controls the A/C

Compressor Clutch Solenoid through the use of a

relay and a control (ground) circuit. This malfunction

detects a low impedance short to ground or open

contact on the A/C clutch relay output, then DTC 88

will set.

Conditions for Setting the DTC

• Driver feedback information shows a high state at

its operation even when commanded low.

Action Taken When the DTC Sets

• The ECM will illuminate Malfunction Indicator lamp

(MIL).

Conditions for Clearing the DTC

Once the ECM determines that a fault(s) has been

rectified then the CEL will switch OFF, although the

fault code will remain in the ECM memory.

Any fault codes will remain in ECM memory until -

1. They are cleared by disconnecting the Battery for

more than 30 seconds.

2. A service tool such as Tech 2 is used to clear them.

3. Ten consecutive starts without logging a fault.

Diagnostic Aids

• This malfunction detects a low impedance short to

battery on the AC clutch relay output.

To diagnose an intermittent fault, check for the

following conditions:
• Poor connection at the ECM-Inspect harness

connections for backed-out terminals, improper

mating, broken locks, improperly formed or

damaged terminals, and poor terminal-to-wire

connection.

• Damaged harness-Inspect the wiring harness for

damage; shorts to Battery Voltage, and Open

circuits. If the harness appears to be OK, observe

the A/C clutch while moving connectors and wiring

harnesses related to the A/C. A sudden clutch

6E1-222 DRIVEABILITY AND EMISSIONS

malfunction will indicate the source of the

intermittent fault.

A/C Clutch Diagnosis

This chart should be used for diagnosing the electrical

portion of the A/C compressor clutch circuit. A Scan

Tool will be used in diagnosing the system. The Scan

Tool has the ability to read the A/C request input to the

ECM. The Scan Tool can display when the ECM has

commanded the A/C clutch ON. The Scan Tool should

have the ability to override the A/C request signal and

energize the A/C compressor relay.

DTC (Flash DTC = 88)

A/C Compressor Clutch Relay High Error

Step

Action

Value(s)

Yes

Was the "On-Board Diagnostic (OBD) System Check"

performed?

Go to Step 2

Go to OBD

System Check

1. Ignition ON, engine OFF.

2. Using the Scan Tool, monitor info for DTC 88.

Does the Scan Tool indicate DTC 88?

Refer to

Diagnostic Aids

Go to Step 3

1. Ignition OFF.

2. Remove the A/C Compressor Clutch Relay from the

Underhood Electrical Center.

3. Ignition ON, engine OFF.

4. Using a Digital Voltmeter (DVM), check for voltage on

the Fused pins of the A/C Compressor Clutch Relay

connector.

Does the DVM read the following value?

12 Volts

Go to Step 4

Go to Step 5

1. Ignition OFF.

2. Disconnect the Engine Control Module (ECM)

connectors from the ECM.

3. Check the A/C Compressor Clutch Relay control circuit

between the ECM and Underhood Electrical Center for

the following conditions:

• A short to battery
Was the problem found?

Verify Repair

Go to Step 5

1. Reinstall the A/C Compressor Clutch Relay.

2. Using a fused jumper, ground the A/C Compressor

Clutch Relay control circuit at the ECM connector.

3. Ignition ON, Engine OFF.

Does the A/C Compressor turn ON?

Go to Step 8

Go to Step 6

1. Ignition OFF.

2. Check the A/C Compressor Clutch circuit between the

A/C Compressor Clutch Relay and A/C Compressor

Clutch for the following conditions:

• A short to battery
Was the problem found?

Verify Repair

Go to Step 7

Replace the A/C Compressor Clutch Relay.

Is the action complete?

Verify Repair

Replace the EPROM or ECM.

Varify Repair

Note) Refer to 6E1-243.

DRIVEABILITY AND EMISSIONS 6E1-223

DIAGNOSTIC TROUBLE CODE (DTC) (Flash DTC = 93)

QUAD DRIVER SUB MODULE

Circuit Description

Quad Driver Sub Module (QDSM) are used by the

engine control module (ECM) to turn ON many of the

current-driven devices that are needed to control

various engine and transmission functions. Each

QDSM is capable of controlling up to 4 separate

outputs by applying ground to the device which the

ECM is commanding ON.

QDSMs have the capability of diagnosing each output

circuit individually. DTC 93 set indicates an improper

voltage level has been detected on a QDSM output.

This DTC detects a short to battery or Open Load or

Short to ground at the QDSM output, then DTC P93

will set.

Conditions for Setting the DTC

• If fault line from the QDSM is detected low.

Action Taken When the DTC Sets

• The ECM will illuminate the malfunction indicator

lamp (MIL).

Conditions for Clearing the DTC

Once the ECM determines that a fault(s) has been

rectified then the CEL will switch OFF, although the

fault code will remain in the ECM memory.

Any fault codes will remain in ECM memory until -

1. They are cleared by disconnecting the Battery for

more than 30 seconds.

2. A service tool such as Tech 2 is used to clear them.

3. Ten consecutive starts without logging a fault.

Diagnostic Aids

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

connectors for backed-out terminals, improper

mating, broken locks, improperly formed or

damaged terminals, and poor terminal-to-wire

connection.

• Damaged harness - Inspect the wiring harness for

damage. If the harness appears to be OK,

disconnect the ECM, turn the ignition ON and

6E1-224 DRIVEABILITY AND EMISSIONS

observe a voltmeter connected to the MIL driver

circuit at the ECM harness connector while moving

connectors and rewiring harnesses relates to the

MIL. A change in voltage will indicate the location of

the fault.

This malfunction detects a:

Short to battery or Open Load or Short to ground at

QDSM output.

DTC (Flash DTC = 93)

Quad Driver Sub Module

Step

Action

Value(s)

Yes

Was the "On-Board Diagnostic (OBD) System Check"

performed?

Go to Step 2

Go to OBD

System

Check

Replace the EPROM or ECM.

Note) Refer to 6E1-243.

Is the action complete?

Verify Repair

Content .. 96 97 98 99 ..