A/c-Heater System - Automatic: Diagnosis Lexus GS I

TROUBLE SHOOTING

CODE TESTING CHART

SELF-DIAGNOSTICS

A/C control assembly monitors system circuits and stores codes in memory if problems are detected. All codes are stored in memory except Codes 22 and 23. Malfunction is current if Code 22 or 23 is displayed. To retrieve stored codes, see RETRIEVING CODES . Codes are displayed at A/C control assembly temperature display.

TESTING

ACCESSORY POWER CIRCUIT TEST

1. Turn ignition on. Inspect CIG fuse, located at fuse block under left side of instrument panel. If fuse is okay, go to next step. If fuse is blown, correct cause and replace fuse.
2. Turn ignition off. Remove A/C control assembly, leaving harness connectors attached. See «A/C CONTROL ASSEMBLY»(ref-36446-S21826621372001010900000) under REMOVAL & INSTALLATION. Turn ignition on.
3. Backprobe between A/C control assembly 10-pin connector terminal A10-2 (Pink/Blue wire) and ground. see scheme 6
4. If battery voltage does not exist, repair Pink/Blue wire between connector and CIG fuse. If battery voltage exists, inspect wiring harness and connectors between battery and A/C control assembly.

AIR INLET DOOR POSITION SENSOR TEST

1. Remove cooling unit. See COOLING UNIT under REMOVAL & INSTALLATION. Unplug air inlet servomotor connector. Measure resistance between servomotor connector terminals No. 3 (Black/White wire) and No. 4 (Red/Yellow wire). (Scheme 4)
2. If resistance is not 4700-7200 ohms, replace air inlet servomotor. If resistance is as specified, go to next step.
3. Connect ohmmeter between servomotor terminals No. 3 (Black/White wire) and No. 5 (Red/Black wire). Apply battery voltage to air inlet servomotor connector terminal No. 2 (Red/White wire). Connect terminal No. 1 (Red/Blue wire) to ground. (Scheme 5)
4. Measure resistance as servomotor operates. Transpose power leads. Again measure resistance. Resistance should be as specified for each door position. See «AIR INLET DOOR POSITION SENSOR SPECIFICATIONS»(ref-36446-S08570968622001010900000) table.

Scheme 4

AIR INLET DOOR POSITION SENSOR SPECIFICATIONS

AIR INLET DOOR SERVOMOTOR TEST

1. Remove cooling unit. See «COOLING UNIT»(ref-36446-S34811460732001010900000) under REMOVAL & INSTALLATION. Unplug air inlet servomotor connector. Connect battery voltage to servomotor terminal No. 2 (Red/White wire). Connect terminal No. 1 (Red/Blue wire) to ground. (Scheme 5)
2. Servomotor lever should move smoothly to recirculation position. Transpose power leads. Servomotor lever should move smoothly to fresh air position. If operation is not as specified, replace servomotor.

Scheme 5

AIR MIX DOOR POSITION SENSOR TEST

1. Remove heater unit. See «HEATER UNIT»(ref-36446-S22356033462001010900000) under REMOVAL & INSTALLATION. Unplug air mix servomotor connector. Measure resistance between servomotor connector terminals No. 3 (Black/White wire) and No. 4 (Red/Yellow wire). (Scheme 6)
2. If resistance is not 4800-7200 ohms, replace air mix servomotor. If resistance is as specified, go to next step.
3. Connect ohmmeter between servomotor terminals No. 3 (Black/White wire) and No. 5 (Blue/Orange wire). Apply battery voltage to air mix servomotor connector terminal No. 2 (Pink wire). Connect terminal No. 1 (Pink/Black wire) to ground. (Scheme 7)
4. As servomotor operates, measure resistance. Transpose power leads. Again measure resistance. Resistance should be as specified for each door position. See «AIR MIX DOOR POSITION SENSOR»(ref-36446-S12644226682001010900000) SPECIFICATIONS table. If resistance is not as specified, replace air mix door servomotor.

AIR MIX DOOR POSITION SENSOR SPECIFICATIONS

Scheme 6

AIR MIX DOOR SERVOMOTOR TEST

1. Remove heater unit. See «HEATER UNIT»(ref-36446-S22356033462001010900000) under REMOVAL & INSTALLATION. Unplug air mix servomotor connector. Apply battery voltage to air mix servomotor connector terminal No. 2 (Pink wire). Connect terminal No. 1 (Pink/Black wire) to ground. (Scheme 7) Servomotor lever should move smoothly to hot side.
2. Transpose power leads. Servomotor lever should move smoothly to cool side. Replace servomotor if it does not function as specified.

Scheme 7

AIR OUTLET DOOR POSITION SENSOR TEST

1. Remove heater unit. See «HEATER UNIT»(ref-36446-S22356033462001010900000) under REMOVAL & INSTALLATION. Unplug air outlet servomotor connector. Measure resistance between servomotor connector terminals No. 3 (Black/White wire) and No. 4 (Red/Yellow wire). (Scheme 8)
2. If resistance is not 4700-7200 ohms, replace air outlet servomotor. If resistance is as specified, go to next step.
3. Connect ohmmeter between servomotor terminals No. 3 (Black/White wire) and No. 5 (Yellow/Black wire). Apply battery voltage to air outlet servomotor connector terminal No. 1 (Yellow/Green wire). Connect terminal No. 2 (Brown/White wire) to ground. (Scheme 9)
4. Measure resistance as servomotor operates. Transpose power leads. Again measure resistance. Resistance should be as specified for each door position. See «AIR OUTLET DOOR POSITION SENSOR SPECIFICATIONS»(ref-36446-S04750014912001010900000) table.

AIR OUTLET DOOR POSITION SENSOR SPECIFICATIONS

Scheme 8

AIR OUTLET DOOR SERVOMOTOR TEST

1. Remove heater unit. See «HEATER UNIT»(ref-36446-S22356033462001010900000) under REMOVAL & INSTALLATION. Unplug air outlet servomotor connector. Apply battery voltage to air the mix servomotor connector terminal No. 1 (Yellow/Green wire). Connect terminal No. 2 (Brown/White wire) to ground. (Scheme 9) Servomotor lever should move smoothly to vent side.
2. Transpose power leads. Servomotor lever should move smoothly to defrost side. If servomotor lever does not function as specified, replace servomotor.

Scheme 9

BACK-UP POWER CIRCUIT TEST

1. Turn ignition off. Inspect ECU-B fuse at engine compartment fuse block. (Scheme 10) If fuse is okay, go to next step. If fuse is blown, correct cause and replace fuse.
2. Remove A/C control assembly, leaving harness connectors attached. Turn ignition on. Backprobe between A/C control assembly connector terminal A10-1 (White/Red wire) and ground. see scheme 6
3. If battery voltage exists, no problem is indicated at this time. If battery voltage does not exist, repair White/Red wire between connector and ECU-B fuse.

Scheme 10

BLOWER MOTOR CIRCUIT TEST

1. Turn ignition off. Remove A/C control assembly, leaving harness connectors attached. See «A/C CONTROL ASSEMBLY»(ref-36446-S21826621372001010900000) under REMOVAL & INSTALLATION. Turn ignition on. Operate blower motor.
2. Measure voltage between ground and A/C control assembly connector terminal A8-9 (Pink/Blue wire). If voltage is 1-3 volts, no problem is indicated at this time. If voltage is not as specified, go to next step.
3. Remove blower motor. See «BLOWER MOTOR»(ref-36446-S16472625642001010900000) under REMOVAL & INSTALLATION. Connect battery voltage to terminal No. 2 (White wire) of blower motor. Connect terminal No. 1 (Black wire) to ground. If blower motor runs smoothly, go to next step. Replace blower motor if it does not run smoothly.
4. Remove blower motor relay, leaving harness connector attached. Relay is located on blower motor case. Turn ignition on. Backprobe between relay terminals as specified. See «BLOWER MOTOR RELAY»(ref-36446-S42941277352001010900000) SPECIFICATIONS table. (Scheme 11) Replace relay as necessary.
5. If relay is okay, inspect wiring between heater main relay and A/C control assembly. Repair wiring as necessary.

BLOWER MOTOR RELAY SPECIFICATIONS

Scheme 11

COMPRESSOR CIRCUIT TEST

1. Remove A/C lock amplifier, leaving harness connector attached. Start engine. Set fan speed to low, medium, or high. Backprobe terminal MCR (Blue/White wire) of A/C lock amplifier. With A/C turned on, battery voltage should exist. With A/C turned off, no voltage should exist. If voltage is as specified, go to next step. If voltage is not as specified, go to step 4).
2. Unplug harness connector at compressor clutch. Connect battery voltage to clutch connector terminal No. 4 (Blue/White wire). If clutch engages, go to next step. Repair or replace clutch if it does not engage.
3. Inspect wiring harness and connectors between compressor and compressor clutch relay. If there are no problems, go to next step. Repair as necessary.
4. Remove A/C control assembly, leaving harness connectors attached. See «A/C CONTROL ASSEMBLY»(ref-36446-S21826621372001010900000) under REMOVAL & INSTALLATION. Start engine. Press AUTO switch. Measure voltage between ground and A/C control assembly connector terminal A8-10 (Blue/Black wire). With A/C turned on, battery voltage should exist. With A/C turned off, no voltage should exist. If voltage is as specified, go to next step. If voltage is not as specified, go to step 6).
5. Inspect wiring harness and connectors between A/C control assembly and A/C lock amplifier. If there are no problems, go to next step. Repair as necessary.
6. Start engine. Set fan speed to low, medium, or high. Backprobe terminal MGC (Black wire) of A/C lock amplifier. With A/C turned on, voltage should be 7.5-14 volts. With A/C turned off, voltage should be zero to 1.5 volts. If voltage is as specified, go to next step. If voltage is not as specified, temporarily substitute known good A/C lock amplifier, and retest system.
7. Inspect wiring harness and connectors between ECM and A/C lock amplifier. If there are no problems, go to next step. Repair as necessary.
8. Turn ignition on. Set fan speed to low, medium, or high. Backprobe terminal ACMG (White wire) of ECM. (Scheme 12) With A/C turned on, voltage should be zero to 3 volts. With A/C turned off, voltage should be 9-14 volts. If voltage is as specified, replace compressor clutch relay. If voltage remains zero to 3 volts, go to next step. If voltage remains 9-14 volts, temporarily substitute known good ECM and retest system.
9. Inspect wiring harness and connectors between compressor relay and A/C lock amplifier. Repair as necessary. If there are no problems, temporarily substitute known good ECM and retest system.

Scheme 12

COMPRESSOR CLUTCH RELAY TEST

1. Remove compressor clutch relay. Relay is located on left side of engine compartment. Inspect for continuity between terminals No. 1 and 2. (Scheme 13) Continuity should not exist. Inspect for continuity between terminals No. 3 and 4. Continuity should exist.
2. Connect battery voltage to terminal No. 3. Connect terminal No. 4 to ground. Inspect for continuity between terminals No. 1 and 2. Continuity should exist. Replace relay if it does not operate as specified.

Scheme 13

COMPRESSOR LOCK SENSOR TEST

Raise and support vehicle. Unplug compressor lock sensor connector, located at compressor. Measure resistance between terminals No. 1 (Gray/Red wire on 1995 models; Black/White wire on 1996 models) and No. 2 (Gray wire) of the compressor lock sensor at specified temperatures. (Scheme 14) See COMPRESSOR LOCK SENSOR SPECIFICATIONS table. Replace sensor if resistance is not as specified.

COMPRESSOR LOCK SENSOR SPECIFICATIONS

Scheme 14

EVAPORATOR TEMPERATURE SENSOR TEST

Remove evaporator temperature sensor. Measure the evaporator temperature sensor resistance at temperatures specified. Refer to the EVAPORATOR TEMPERATURE SENSOR RESISTANCE SPECIFICATIONS table. If resistance is not as specified, replace sensor.

EVAPORATOR TEMPERATURE SENSOR RESISTANCE SPECIFICATIONS

HEATER MAIN RELAY CIRCUIT TEST

1. Turn ignition on. Inspect GAUGE fuse at fuse block under left side of instrument panel. If fuse is okay, go to next step. If fuse is blown, correct cause and replace the fuse. Remove the A/C control assembly, leaving the harness connectors attached. Refer to «A/C CONTROL ASSEMBLY»(ref-36446-S21826621372001010900000) under REMOVAL & INSTALLATION. Turn ignition off. Ensure blower switch is off.
2. Check for voltage at A/C control assembly connector between terminal A8-16 (Blue/Yellow wire on 1995 models; Gray/Black wire on 1996 models) and ground. see scheme 6 If battery voltage does not exist, go to next step. If battery voltage exists, repair short to voltage in Blue/Yellow wire (or Gray/Black wire) between connector and heater main relay.
3. Turn ignition on. Check for voltage at A/C control assembly connector between terminal A8-16 (Blue/Yellow wire on 1995 models; Gray/Black wire on 1996 models) and ground. If battery voltage does not exist, go to next step. If battery voltage exists, no problem is indicated at this time.
4. Remove heater main relay. Relay is located on left side of engine compartment. Test for continuity between relay terminals No. 4 and 5. (Scheme 15) Continuity should not exist. Test for continuity between terminals No. 1 and 3, and between terminals No. 2 and 4. Continuity should exist.
5. Apply battery voltage to relay terminal No. 3. Connect terminal No. 1 to ground. Test for continuity between terminals No. 2 and 4. Continuity should not exist. Test for continuity between terminals No. 4 and 5. Continuity should exist. Replace relay if it does not operate as specified. If relay is okay, inspect wiring harness and connectors between A/C control assembly and battery.

Scheme 15

IGNITION POWER & GROUND CIRCUITS TEST

1. Turn ignition on. Inspect GAUGE fuse at fuse block under left side of instrument panel. If fuse is okay, go to next step. If fuse is blown, correct cause and replace fuse. Remove A/C control assembly, leaving harness connectors attached.
2. Backprobe A/C control assembly connector between terminals A10-6 (Black/Yellow wire) and A10-5 (White/Black wire). see scheme 6 If battery voltage does not exist, go to next step. If battery voltage exists, no problem is indicated at this time.
3. Turn ignition off. Measure resistance between terminal A10-5 (White/Black wire) of A/C control assembly and ground. If resistance is not less than one ohm, repair open White/Black wire. If resistance is less than one ohm, wire is okay. Inspect wiring harness and connectors between A/C control assembly and battery. Repair as necessary.

IN-VEHICLE TEMPERATURE SENSOR TEST

Remove panel underneath instrument panel. Unplug in-vehicle temperature sensor. see scheme 1 Measure sensor resistance while heating sensor. See IN-VEHICLE TEMPERATURE SENSOR SPECIFICATIONS table. If resistance is not as specified, replace sensor.

IN-VEHICLE TEMPERATURE SENSOR SPECIFICATIONS

MAXIMUM COOL DOOR SERVOMOTOR TEST

1. Warm engine to normal operating temperature. Perform «RETRIEVING CODES»(ref-36446-S17949974872001010900000) . After system enters self-diagnostic mode, perform «ACTUATOR CHECK»(ref-36446-S15494907242001010900000) . Press A/C button to enter step mode and display codes.
2. Rotate temperature control knob while verifying maximum cool door operation by changes in blower output and sound of door operation. See appropriate MAXIMUM COOLING DOOR SERVOMOTOR OPERATION table. MAXIMUM COOLING DOOR SERVOMOTOR OPERATION (1995) Code Door Position 20-21 Open 22-29 Closed MAXIMUM COOLING DOOR SERVOMOTOR OPERATION (1996) Code Door Position 0-1 Open 2-9 Closed
3. If maximum cool door servomotor functions as specified, no problem is indicated at this time. If maximum cool door servomotor does not function as specified, go to next step.
4. Remove heater unit. See «HEATER UNIT»(ref-36446-S22356033462001010900000) under REMOVAL & INSTALLATION. Unplug maximum cool door servomotor connector. Apply battery voltage to maximum cool servomotor connector terminal No. 4 (Black/Yellow wire). Connect terminal No. 1 (Blue/Red wire) to ground. Servomotor lever should move smoothly to closed position.
5. With battery voltage still connected to terminal No. 4, remove ground from terminal No. 1. Ground terminal No. 3 (Yellow wire). Servomotor lever should move smoothly to open position. If servomotor functions as specified, go to next step. Replace servomotor if it does not function as specified.
6. Inspect wiring harness and connectors between servomotor and A/C control assembly. Repair as necessary. If wiring harness and connectors are okay, temporarily substitute a known good A/C control assembly, then retest system.

OUTSIDE TEMPERATURE SENSOR TEST

1. Remove clip and outside temperature sensor from left side of bumper reinforcement. see scheme 1 Unplug outside temperature sensor connector. Measure the sensor resistance while heating sensor. See the «OUTSIDE TEMPERATURE SENSOR SPECIFICATIONS»(ref-36446-S10245850982001010900000) table.
2. If resistance is not as specified, replace sensor. If resistance is within specification, inspect wiring harness and connectors between sensor and A/C control assembly. Repair as necessary. If wiring harness and connectors are okay, substitute a known good A/C control assembly, then retest system. If problem does not exist with known good A/C control assembly, replace original A/C control assembly.

OUTSIDE TEMPERATURE SENSOR SPECIFICATIONS

PRESSURE SWITCH TEST

1. Pressure switch is located near receiver-drier. (Scheme 16) Connect A/C manifold gauge set. Start engine. Turn blower and A/C on. Observe system pressure. With pressure switch connector disconnected, test for continuity between pressure switch terminals No. 1 and 4.
2. Continuity should not exist if high side pressure is less than 326 psi (23 kg/cm 2 ) or higher than 455 psi (32 kg/cm 2 ). Continuity should exist if high side pressure is greater than 326 psi (23 kg/cm 2 ) or lower than 455 psi (32 kg/cm 2 ). If continuity is not as specified, replace pressure switch.

Scheme 16

RADIATOR FAN RELAY TEST

1. Remove radiator fan relay. Relay is located on left side of engine compartment. Inspect for continuity between terminals No. 3 and 5. (Scheme 17) Continuity should not exist. Inspect for continuity between terminals No. 1 and 2. Continuity should exist.
2. Connect battery voltage to terminal No. 1. Connect terminal No. 2 to ground. Inspect for continuity between terminals No. 3 and 5. Continuity should exist. Replace relay if it does not operate as specified.

Scheme 17

RADIATOR FAN MAIN RELAY TEST

1. Remove radiator fan main relay. Relay is located on left side of engine compartment. Inspect for continuity between terminals No. 1 and 3, and terminals No. 2 and 4. (Scheme 15) Continuity should exist. Inspect for continuity between terminals No. 4 and 5. Continuity should not exist.
2. Connect battery voltage to terminal No. 1. Connect terminal No. 3 to ground. Inspect for continuity between terminals No. 4 and 5. Continuity should exist. Inspect for continuity between terminals No. 2 and 4. Continuity should not exist. Replace relay if it does not operate as specified.

SELF-DIAGNOSTIC CIRCUIT TEST

1. Turn ignition on. Measure voltage between Data Link Connector No. 2 (DLC2) terminals TC and AC. (Scheme 18) DLC2 is located behind left side of instrument panel. If battery voltage exists, no problem is indicated at this time.
2. If battery voltage does not exist, inspect wiring harness and connectors between A/C control assembly, DLC2, and ground. Repair as necessary. If wiring and connectors are okay, temporarily substitute a known good A/C control assembly, then retest system.

Scheme 18

SOLAR SENSOR TEST

1. Remove glove box and solar sensor. Unplug sensor harness connector. Cover sensor with cloth. Connect positive lead of ohmmeter to Green/Black wire terminal, and negative lead to Red/Yellow wire terminal of solar sensor. Measure and record resistance between sensor terminals.
2. Remove cloth. Subject sensor to bright light. Again measure sensor. See «SOLAR SENSOR RESISTANCE SPECIFICATIONS»(ref-36446-S12915337252001010900000) table. If resistance is not as specified, replace sensor.

SOLAR SENSOR RESISTANCE SPECIFICATIONS

COOLANT (WATER) TEMPERATURE SENSOR TEST

Remove the coolant (water) temperature sensor. Refer to COOLANT (WATER) TEMPERATURE SENSOR under REMOVAL & INSTALLATION. Place sensor and thermometer in water. Measure resistance between sensor terminals as water is heated. If resistance does not measure as specified, replace the coolant temperature sensor. Refer to the COOLANT TEMPERATURE SENSOR RESISTANCE SPECIFICATIONS table.

COOLANT TEMPERATURE SENSOR RESISTANCE SPECIFICATIONS