AIR SUSPENSION SYSTEM, Diagnostic DTC:C1751/51

DTC Code DTC Name
C1751/51 Compressor Relay Coil Malfunction

DESCRIPTION

When the "up" side of the height control switch is pressed, a signal is sent from terminal RC of the suspension control ECU to the AIR SUS relay to turn the relay on.

As a result, the current flows to the AIR SUS relay coil, closing the relay contact, and then battery positive voltage is applied to the height control compressor, which causes compressed air to raise the vehicle height.

DTC No.

Detection Item

DTC Detection Condition

Trouble Area

Warning Indicate

C1751/51

Compressor Relay Coil Malfunction

Either condition is met:

  • With the AIR SUS relay inactivated, an open signal of the AIR SUS relay is detected for 1 second or more.

  • With the AIR SUS relay activated, a short signal of the AIR SUS relay is detected 8 times successively.

  • Harness or connector

  • AIR SUS relay (Suspension control relay)

  • Suspension control ECU

Indicated
Tip:

Once the suspension control ECU stores DTC C1751/51 in memory, vehicle height control is suspended until a normal signal is input to the suspension control ECU from the AIR SUS relay. However, control is resumed if the engine switch is turned off and then on (IG) again.

WIRING DIAGRAM

C218583E04

CAUTION / NOTICE / HINT

Note:

When replacing the suspension control ECU, perform registration (Click here).

Tip:

If DTC C1782/82 is output at the same time as C1751/51, perform the inspection necessary for DTC C1782/82 first (See page ).

Click here

PROCEDURE

  1. PERFORM ACTIVE TEST USING INTELLIGENT TESTER (COMPRESSOR MOTOR RELAY)

    1. Turn the engine switch off.

    2. Connect the intelligent tester to the DLC3.

    3. Turn the engine switch on (IG).

    4. Turn the intelligent tester on.

    5. Enter the following menus: Chassis / Air suspension / Active Test.

      Chassis > Air suspension > Active Test

      Tester Display

      Measurement Item

      Control Range

      Diagnostic Note

      Compressor Motor Relay

      AIR SUS relay

      ON or OFF

      • The operating sound of the motor can be heard.

      • When the Active Test is performed, Motor Relay in the Data List changes between ON and OFF accordingly.

      OK

      Operation of motor can be heard.

      Result

      Result

      Proceed to

      NG

      A

      OK (When troubleshooting according to problem symptoms table)

      B

      OK (When troubleshooting according to DTC chart)

      C
    B

    PROCEED TO NEXT SUSPECTED AREA SHOWN IN PROBLEM SYMPTOMS TABLE

    Click here

    C

    USE SIMULATION METHOD TO CHECK

    Click here

    A

  2. INSPECT SUSPENSION CONTROL RELAY (AIR SUS)

    1. Turn the engine switch off.

    2. Remove the AIR SUS relay from the engine room relay block.

    3. C149624C01

      *1

      AIR SUS Relay

      Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection

      Condition

      Specified Condition

      3 - 5

      12 V battery voltage is not applied to terminal 1 and 2

      10 kΩ or higher

      12 V battery voltage is applied to terminal 1 and 2

      Below 1 Ω

      Result

      Result

      OK

      NG
    NG

    REPLACE SUSPENSION CONTROL RELAY (AIR SUS)

    OK

  3. CHECK HARNESS AND CONNECTOR (SUSPENSION CONTROL ECU - AIR SUS RELAY)

    1. Disconnect the R22 suspension control ECU connector.

    2. Remove the AIR SUS relay from the engine room relay block.

    3. Measure the resistance according to the value(s) in the table below.

      Standard Resistance

      Tester Connection

      Condition

      Specified Condition

      R22-22 (RC) - Engine room relay block AIR SUS relay terminal 1

      Always

      Below 1 Ω

      R22-22 (RC) - Body ground

      Always

      10 kΩ or higher

      Engine room relay block AIR SUS relay terminal 2 - Body ground

      Always

      Below 1 Ω

      Result

      Result

      OK

      NG
    OK

    REPLACE SUSPENSION CONTROL ECU

    Click here

    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR