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Test G (Code 51) Lowering Not Detected

  1. Enter Functional Test 32. See FUNCTIONAL TEST under TESTING & DIAGNOSIS. During this test, vent solenoid valve should cycle on and off repeatedly. It should be heard at left front wheel opening. If valve cycles on and off, go to step 5). If valve does not cycle, go to next step.
  2. Remove air cleaner intake tube and air compressor shield. Inspect compressor for obvious signs of damage. Disconnect electrical connector and inspect for damage. Ensure terminals are fully seated in connector. Measure voltage between circuit No. 421 (Pink wire) in harness connector and ground. Meter should pulse between zero volts and battery voltage. If voltage pulses, replace compressor assembly. If voltage does not pulse, go to next step.
  3. Measure voltage between circuit No. 414 (Orange/Red wire) at harness connector and ground. Battery voltage should be indicated. If battery voltage is present, go to next step. If battery voltage is not indicated, repair open in circuit No. 414 (Orange/Red wire).
  4. Turn air suspension switch to OFF position. Disconnect control module connectors. Measure resistance between circuit No. 421 (Pink wire) at compressor connector and pin No. 24 of control module connector. See Fig 1 . If ohmmeter reading is less than 10 ohms, replace control module. If reading is 10 ohms or more, repair open in circuit No. 421 (Pink wire).
    Fig 1: Vent Solenoid Testing
    G90E14310
  5. Enter Functional Test Code 33. See FUNCTIONAL TEST under TESTING & DIAGNOSIS. Leave air suspension switch in ON position and raise vehicle on hoist. Feel each spring solenoid valve to see if it is cycling ON and OFF. If valves cycle, go to step 10). If one or both valves are not cycling, DO NOT exit Functional Test Code 33. Go to next step.
  6. Disconnect inoperative spring solenoid connector. Measure voltage between both circuits in connector. Voltmeter should pulse between zero volts and battery voltage. If voltmeter pulses, replace inoperative spring solenoid. If voltmeter does not pulse, exit Functional Test Code 33. Go to next step.
  7. Measure voltage between circuit No. 414 (Orange/Red wire) at spring solenoid connector and good ground. If battery voltage is indicated, go to next step. If battery voltage is not indicated, repair open in circuit No. 414 (Orange/Red wire).
  8. Turn air suspension switch to OFF position. Disconnect control module connectors. Measure resistance of left spring solenoid control circuit between solenoid connector and Black control module connector pin No. 13. See Fig 2 . Repeat procedure on right air spring solenoid connector and Black control module connector pin No. 25. If resistance in either/or both circuits is less than 10 ohms, replace control module and both air spring solenoid valves. If resistance on either/or both circuits is 10 ohms or greater, repair open in circuit in question between control module and solenoid valve connector.
    Fig 2: Spring Solenoid Control Circuits
    G90F14311
    NOTE: Resistance measurements in the following procedure checks air spring solenoid valve coil and diode condition. Digital ohmmeters will not pass enough current through diode to check its condition. Use Rotunda Tester (059-00010) or equivalent analog ohmmeter.
  9. Turn air suspension switch to OFF position. Disconnect control module connectors. Turn air suspension switch to ON position. Measure resistance between pins No. 13 and 1 on control module connectors. Reverse leads and measure resistance again between pins No. 13 and 1. Ohmmeter should indicate 15-18 ohms one way, and 5-10 ohms less the other way. For terminal identification, see Figure . 9a) If higher reading is 15-18 ohms and lower reading is 5-10 ohms less than higher reading, go to next step. If both readings are the same or 0-18 ohms, replace spring solenoid. Repeat SERVICE BAY DIAGNOSTICS under TESTING & DIAGNOSIS.
  10. Measure resistance between pins No. 25 and 1 on control module connectors. Reverse leads and measure resistance again between pins No. 25 and 1. Ohmmeter should indicate 15-18 ohms one way, and 5-10 ohms less the other way. For terminal identification, see Figure . If readings are within specification, replace control module. Repeat SERVICE BAY DIAGNOSTICS under TESTING & DIAGNOSIS, the go to next step. If both readings are the same, 0-18 ohms, replace faulty spring solenoid. Repeat SERVICE BAY DIAGNOSTICS, then go to next step.
  11. Leave Super Star II tester in Functional Test mode, but do not select test (tester button should be depressed down). Leave air suspension switch in ON position. Making sure Super Star II tester is within reach, raise vehicle on hoist. Ensure height sensor is attached to both ball studs. Height sensor damage must be repaired before continuing.
  12. Disconnect air lines at both spring solenoid valves. Remove air spring solenoid heat shields, if equipped. Enter Super Star II tester Functional Test Code 33 to cycle air spring solenoid valves. See FUNCTIONAL TEST under TESTING & DIAGNOSIS. Air should flow from each air spring solenoid when it is cycled open. If air flows from both solenoid valves, exit Functional Test Code 33. Connect solenoid air lines and install heat shields and go to next step. If air does not flow from one or both solenoid valves, replace inoperative solenoid valve. Repeat SERVICE BAY DIAGNOSTICS under TESTING & DIAGNOSIS.
  13. Lower vehicle. There should be nothing supporting vehicle. Measure distance between top center of rear wheel opening lip and bottom of wheel (not bottom of tire). Measurement should be 24-25" (610-635 mm) when vehicle is at correct riding height. If vehicle is higher, go to next step. If vehicle is lower, go to step 16). In following procedure, rear of vehicle may drop rapidly once Functional Test Code 23 is entered.
  14. Remove air cleaner assembly and shield from compressor assembly. Disconnect air line at compressor drier. Enter Super Star II tester Functional Test Code 23 (vent rear). See FUNCTIONAL TEST under TESTING & DIAGNOSIS. Air should flow from disconnected air line and vehicle should drop about one inch in 10-20 seconds. If there is little or no airflow and vehicle does not lower, repair air line from compressor to solenoid valves for blockage or kinks. Repeat SERVICE BAY DIAGNOSTICS under TESTING & DIAGNOSIS. If there is airflow from air line and vehicle drops, exit Functional Test Code 23 before rear of vehicle becomes too low and go to next step.
  15. Remove drier from compressor. Connect air line to air drier. Enter Functional Test Code 23 (vent rear). See FUNCTIONAL TEST under TESTING & DIAGNOSIS. If little or no air flows through drier, replace air drier. See AIR DRIER under REMOVAL & INSTALLATION. Repeat SERVICE BAY DIAGNOSTICS under TESTING & DIAGNOSIS. If air flows through drier, replace air compressor assembly. Repeat SERVICE BAY DIAGNOSTICS under TESTING & DIAGNOSIS.
  16. Enter Functional Test Code 26 (compress rear). See FUNCTIONAL TEST under TESTING & DIAGNOSIS. Exit Functional Test Code 26 when rear of vehicle is raised about 2" (50 mm) above riding height. Distance should be about 26-27" (660-685 mm) from top center of rear wheel opening lip to bottom of wheel (not bottom of tire). If vehicle raises, return to step 14). If vehicle does not raise, but air compressor runs, exit Functional Test Code 26 and go to next step. If rear of vehicle does not raise and air compressor does not run, go to TEST H (CODE 54), UNABLE TO DETECT REAR RAISING.
    CAUTION: Support rear of vehicle on frame for next test. If rear of vehicle is supported by axle, air springs will be damaged.
  17. Raise rear of vehicle and support on frame. Disconnect air line from air drier. Enter Functional Test Code 26 (compress rear). See FUNCTIONAL TEST under TESTING & DIAGNOSIS. Air should flow from air drier while compressor is running. If there is airflow from drier, repair blocked or kinked air line. If there is little or no airflow from drier, exit Functional Test Code 26. Go to next step.
  18. Remove air drier from compressor. Enter Functional Test Code 26 (compress rear). See FUNCTIONAL TEST under TESTING & DIAGNOSIS. Air should flow from air drier fitting on compressor while compressor is running. If air flows from compressor, replace air drier. If there is little or no airflow from compressor, replace compressor assembly.
CAUTION: Enter Functional Test Code 26 (compress rear) and fill air springs for about 90 seconds before lowering rear of vehicle.
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