Content .. 95 96 97 98 ..

Isuzu engine C22NE / 22LE / 20LE. Manual - part 97

DRIVEABILITY AND EMISSIONS 6E1-217

A/C

Compressor

Relay

Control

A16

MAG

Clutch

(Compressor)

Relay

Thermo

(1)

(2)

(3)

(4)

Relay:A/C

Compressor

Joint

To HA09

0.5

GR/R

B10

0.5

G/B

HOT IN START AND RUN

(2)

(1)

(4)

(3)

Engine

Control

Module

(ECM)

DIAGNOSTIC TROUBLE CODE (DTC) (Flash DTC = 87)

A/C COMPRESSOR CLUTCH RELAY LOW 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 87

will set.

Conditions for Setting the DTC

• Driver feedback information shows a low state at its

operation even when commanded high.

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

ground or open contact 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.

6E1-218 DRIVEABILITY AND EMISSIONS

• Damaged harness-Inspect the wiring harness for

damage; shorts to Ground, 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 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 = 87)

A/C Compressor Clutch Relay Low 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 87.

Does the Scan Tool indicate DTC 87?

Refer to

Diagnostic Aids

Go to Step 3

1. Ignition OFF.

2. Check for an open circuit at the pressure switch and

thermo switch.

And also check for an open circuit at the wire harness

between pressure switch and the ECM, pressure

switch and thermo switch, thermo switch and the Fuse.

Repair it necessary.

Verify Repair

Go to Step 4

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

Underhood Electrical Center.

2. Ignition ON, engine OFF.

3. 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 6

Go to Step 5

Check the suspect circuit(s) between the A/C Compressor

Clutch Relay connector and the Fuse for the following

conditions:
• A short to ground
• An open circuit
Was the problem found?

Verify Repair

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 ground
• An open circuit
Was the problem found?

Verify Repair

Go to Step 7

DRIVEABILITY AND EMISSIONS 6E1-219

DTC (Flash DTC = 87)

A/C Compressor Clutch Relay Low Error (Cont'd)

Step

Action

Value(s)

Yes

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 10

Go to Step 8

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 ground
• An open circuit
Was the problem found?

Verify Repair

Go to Step 9

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.

6E1-220 DRIVEABILITY AND EMISSIONS

Content .. 95 96 97 98 ..