Inspection Procedure 29: A/C Pressure Sensor System

OPERATION

A power voltage of 5 V is applied to the A/C pressure sensor power terminal (terminal No. 3) from the engine-A/T-ECU (terminal No. 97) and is earthed to the engine-A/T-ECU (terminal No. 96) from the A/C pressure sensor (terminal No. 1).

The sensor signal is inputted to the engine-A/T-ECU (terminal No. 118) from the A/C pressure sensor output terminal (terminal No. 2).

FUNCTION

The A/C pressure sensor detects the A/C refrigerant pressure and inputs the pressure signal to the engine-A/T-ECU. The engine-ECU uses the signal for ON/OFF control of the magnet clutch of the A/C compressor.

PROBABLE CAUSE

Failed A/C pressure sensor

Open/short circuit in A/C pressure sensor circuit or loose connector contact

Failed engine-A/T-ECU

DIAGNOSIS PROCEDURE

STEP 1. Connector check: A-02 A/C pressure sensor connector

Q: Is the check result normal?

YES: Go to Step 2

.
NO: Repair.

STEP 2. Perform voltage measurement at A-02 A/C pressure sensor connector.

Disconnect connector, and measure at harness side.

Ignition switch: ON

Voltage between terminal No. 3 and earth.

OK: 4.9 - 5.1 V

Q: Is the check result normal?

YES: Go to Step 8

.
NO: Go to Step 3

STEP 3. Perform voltage measurement at C-137 engine-A/T-ECU connector.

Measure engine-A/T-ECU terminal voltage.

Ignition switch: ON

Voltage between terminal No. 97 and earth.

OK: 4.9 - 5.1 V

Q: Is the check result normal?

YES: Go to Step 4

.
NO: Go to Step 5

STEP 4. Connector check: C-137 engine-A/T-ECU connector

Q: Is the check result normal?

YES:

Check intermediate connector A-14, and repair if necessary. If intermediate connector is normal, check and repair harness between A-02 (terminal No. 3) A/C pressure sensor connector and C-137 (terminal No. 97) engine-A/T-ECU connector.

Check power line for open circuit.

NO: Repair.

STEP 5. Connector check: C-137 engine-A/T-ECU connector

Q: Is the check result normal?

YES: Go to Step 6

.
NO: Repair.

STEP 6. Check harness between A-02 (terminal No. 3) A/C pressure sensor connector and C-137 (terminal No. 97) engine-A/T-ECU connector.

NOTE: Before checking harness, check intermediate connector A-14, and repair if necessary.

Check power line for short circuit.

Q: Is the check result normal?

YES: Go to Step 7

.
NO: Repair.

STEP 7. Check the trouble symptoms.

Q: Does trouble symptom persist?

YES: Replace engine-A/T-ECU.
NO: Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points

STEP 8. Perform resistance measurement at A-02 A/C pressure sensor connector.

Disconnect connector, and measure at harness side.

Resistance between terminal No. 1 and earth

OK: 2 Ω or less

Q: Is the check result normal?

YES: Go to Step 11

.
NO: Go to Step 9

STEP 9. Connector check: C-137 engine-A/T-ECU connector

Q: Is the check result normal?

YES: Go to Step 10

.
NO: Repair.

STEP 10. Check harness between A-02 (terminal No. 1) A/C pressure sensor connector and C-137 (terminal No. 96) engine-A/T-ECU connector.

NOTE: Before checking harness, check intermediate connectors C-105 and C-116, and repair if necessary.

Check earthing line for open circuit or damage.

Q: Is the check result normal?

YES: Go to Step 7

.
NO: Repair.

STEP 11. Perform voltage measurement at A-02 A/C pressure sensor connector.

Use special tool test harness (MB991348) to connect connector, and measure at pick-up harness.

Ignition switch: ON

Voltage between terminal No. 3 and earth.

OK: 4.9 - 5.1 V

Q: Is the check result normal?

YES: Go to Step 13

.
NO: Go to Step 12

STEP 12. Connector check: C-137 engine-A/T-ECU connector

Q: Is the check result normal?

YES:

Check intermediate connector A-14, and repair if necessary. If intermediate connector is normal, check and repair harness between A-02 (terminal No. 3) A/C pressure sensor connector and C-137 (terminal No. 97) engine-A/T-ECU connector.

Check power line for damage.

NO: Repair.

STEP 13. Perform voltage measurement at A-02 A/C pressure sensor connector.

Use special tool test harness (MB991348) to connect connector, and measure at pick-up harness.

Ignition switch: ON

Voltage between terminal No. 1 and earth.

OK: 0.5 V or less

Q: Is the check result normal?

YES: Go to Step 15

.
NO: Go to Step 14

STEP 14. Connector check: C-137 engine-A/T-ECU connector

Q: Is the check result normal?

YES:

Check intermediate connectors C-105 and C-116, and repair if necessary. If intermediate connectors are normal, check and repair harness between A-02 (terminal No. 1) A/C pressure sensor connector and C-137 (terminal No. 96) engine-A/T-ECU connector.

Check earthing line for damage.

NO: Repair.

STEP 15. Perform voltage measurement at A-02 A/C pressure sensor connector.

Use special tool test harness (MB991348) to connect connector, and measure at pick-up harness.

Engine: Running at idle

A/C switch: ON

Voltage between terminal No. 2 and earth.

OK:

2.2 V or more (When A/C is "MAX, COOL" condition)

1.8 V or less (When A/C is "MAX, HOT" condition)

Q: Is the check result normal?

YES: Go to Step 18

.
NO: Go to Step 16

STEP 16. Connector check: C-137 engine-A/T-ECU connector

Q: Is the check result normal?

YES: Go to Step 17

.
NO: Repair.

STEP 17. Check harness between A-02 (terminal No. 2) A/C pressure sensor connector and C-137 (terminal No. 118) engine-A/T-ECU connector.

NOTE: Before checking harness, check intermediate connectors C-104 and C-116, and repair if necessary.

Check output line for open circuit and damage.

Q: Is the check result normal?

YES: Replace A/C pressure sensor.
NO: Repair.

STEP 18. Perform voltage measurement at C-137 engine-A/T-ECU connector.

Measure engine-A/T-ECU terminal voltage.

Engine: Running at idle

A/C switch: ON

Voltage between terminal No. 118 and earth.

OK:

2.2 V or more (When A/C is "MAX, COOL" condition)

1.8 V or more (When A/C is "MAX, HOT" condition)

Q: Is the check result normal?

YES: Go to Step 20

.
NO: Go to Step 19

STEP 19. Connector check: C-137 engine-A/T-ECU connector

Q: Is the check result normal?

YES:

Check intermediate connectors C-104 and C-116, and repair if necessary. If intermediate connectors are normal, check and repair harness between A-02 (terminal No. 2) A/C pressure sensor connector and C-137 (terminal No. 118) engine-A/T-ECU connector.

Check power line for short circuit and damage.

NO: Repair.

STEP 20. Connector check: C-137 engine-A/T-ECU connector

Q: Is the check result normal?

YES: Go to Step 7

.
NO: Repair.


Inspection Procedure 29: A/C Pressure Sensor System

OPERATION A power voltage of 5 V is applied to the A/C pressure sensor power terminal (terminal No. 3) from the engine-A/T-ECU (terminal No. 97) and is earthed to the engine-A/T-ECU (terminal No. 96) from the A/C pressure sensor (terminal No. 1). The sensor signal is inputted to the engine-A/T-ECU (terminal No. 118) from the A/C pressure sensor output terminal (terminal No. 2).
FUNCTION The A/C pressure sensor detects the A/C refrigerant pressure and inputs the pressure signal to the engine-A/T-ECU. The engine-ECU uses the signal for ON/OFF control of the magnet clutch of the A/C compressor.
PROBABLE CAUSE Failed A/C pressure sensor Open/short circuit in A/C pressure sensor circuit or loose connector contact Failed engine-A/T-ECU
	DIAGNOSIS PROCEDURE

	STEP 1. Connector check: A-02 A/C pressure sensor connector
	Q: Is the check result normal? YES: Go to Step 2 . NO: Repair.
	STEP 2. Perform voltage measurement at A-02 A/C pressure sensor connector.
	Disconnect connector, and measure at harness side. Ignition switch: ON Voltage between terminal No. 3 and earth. OK: 4.9 - 5.1 V Q: Is the check result normal? YES: Go to Step 8 . NO: Go to Step 3 .
	STEP 3. Perform voltage measurement at C-137 engine-A/T-ECU connector.
	Measure engine-A/T-ECU terminal voltage. Ignition switch: ON Voltage between terminal No. 97 and earth. OK: 4.9 - 5.1 V Q: Is the check result normal? YES: Go to Step 4 . NO: Go to Step 5 .
	STEP 4. Connector check: C-137 engine-A/T-ECU connector
	Q: Is the check result normal? YES: Check intermediate connector A-14, and repair if necessary. If intermediate connector is normal, check and repair harness between A-02 (terminal No. 3) A/C pressure sensor connector and C-137 (terminal No. 97) engine-A/T-ECU connector. Check power line for open circuit. NO: Repair.
	STEP 5. Connector check: C-137 engine-A/T-ECU connector
	Q: Is the check result normal? YES: Go to Step 6 . NO: Repair.
	STEP 6. Check harness between A-02 (terminal No. 3) A/C pressure sensor connector and C-137 (terminal No. 97) engine-A/T-ECU connector.
	NOTE: Before checking harness, check intermediate connector A-14, and repair if necessary. Check power line for short circuit. Q: Is the check result normal? YES: Go to Step 7 . NO: Repair.
	STEP 7. Check the trouble symptoms. Q: Does trouble symptom persist? YES: Replace engine-A/T-ECU. NO: Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points ).
	STEP 8. Perform resistance measurement at A-02 A/C pressure sensor connector.
	Disconnect connector, and measure at harness side. Resistance between terminal No. 1 and earth OK: 2 Ω or less Q: Is the check result normal? YES: Go to Step 11 . NO: Go to Step 9 .
	STEP 9. Connector check: C-137 engine-A/T-ECU connector
	Q: Is the check result normal? YES: Go to Step 10 . NO: Repair.
	STEP 10. Check harness between A-02 (terminal No. 1) A/C pressure sensor connector and C-137 (terminal No. 96) engine-A/T-ECU connector.
	NOTE: Before checking harness, check intermediate connectors C-105 and C-116, and repair if necessary. Check earthing line for open circuit or damage. Q: Is the check result normal? YES: Go to Step 7 . NO: Repair.
	STEP 11. Perform voltage measurement at A-02 A/C pressure sensor connector.
	Use special tool test harness (MB991348) to connect connector, and measure at pick-up harness. Ignition switch: ON Voltage between terminal No. 3 and earth. OK: 4.9 - 5.1 V Q: Is the check result normal? YES: Go to Step 13 . NO: Go to Step 12 .
	STEP 12. Connector check: C-137 engine-A/T-ECU connector
	Q: Is the check result normal? YES: Check intermediate connector A-14, and repair if necessary. If intermediate connector is normal, check and repair harness between A-02 (terminal No. 3) A/C pressure sensor connector and C-137 (terminal No. 97) engine-A/T-ECU connector. Check power line for damage. NO: Repair.
	STEP 13. Perform voltage measurement at A-02 A/C pressure sensor connector.
	Use special tool test harness (MB991348) to connect connector, and measure at pick-up harness. Ignition switch: ON Voltage between terminal No. 1 and earth. OK: 0.5 V or less Q: Is the check result normal? YES: Go to Step 15 . NO: Go to Step 14 .
	STEP 14. Connector check: C-137 engine-A/T-ECU connector
	Q: Is the check result normal? YES: Check intermediate connectors C-105 and C-116, and repair if necessary. If intermediate connectors are normal, check and repair harness between A-02 (terminal No. 1) A/C pressure sensor connector and C-137 (terminal No. 96) engine-A/T-ECU connector. Check earthing line for damage. NO: Repair.
	STEP 15. Perform voltage measurement at A-02 A/C pressure sensor connector.
	Use special tool test harness (MB991348) to connect connector, and measure at pick-up harness. Engine: Running at idle A/C switch: ON Voltage between terminal No. 2 and earth. OK: 2.2 V or more (When A/C is "MAX, COOL" condition) 1.8 V or less (When A/C is "MAX, HOT" condition) Q: Is the check result normal? YES: Go to Step 18 . NO: Go to Step 16 .
	STEP 16. Connector check: C-137 engine-A/T-ECU connector
	Q: Is the check result normal? YES: Go to Step 17 . NO: Repair.
	STEP 17. Check harness between A-02 (terminal No. 2) A/C pressure sensor connector and C-137 (terminal No. 118) engine-A/T-ECU connector.
	NOTE: Before checking harness, check intermediate connectors C-104 and C-116, and repair if necessary. Check output line for open circuit and damage. Q: Is the check result normal? YES: Replace A/C pressure sensor. NO: Repair.
	STEP 18. Perform voltage measurement at C-137 engine-A/T-ECU connector.
	Measure engine-A/T-ECU terminal voltage. Engine: Running at idle A/C switch: ON Voltage between terminal No. 118 and earth. OK: 2.2 V or more (When A/C is "MAX, COOL" condition) 1.8 V or more (When A/C is "MAX, HOT" condition) Q: Is the check result normal? YES: Go to Step 20 . NO: Go to Step 19 .
	STEP 19. Connector check: C-137 engine-A/T-ECU connector
	Q: Is the check result normal? YES: Check intermediate connectors C-104 and C-116, and repair if necessary. If intermediate connectors are normal, check and repair harness between A-02 (terminal No. 2) A/C pressure sensor connector and C-137 (terminal No. 118) engine-A/T-ECU connector. Check power line for short circuit and damage. NO: Repair.
	STEP 20. Connector check: C-137 engine-A/T-ECU connector
	Q: Is the check result normal? YES: Go to Step 7 . NO: Repair.