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Test G (Code 51): Lowering Not Detected

NOTE: For TEST "D" pin test connector locations. See Fig 1 and Fig 2.
  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. See Fig 1 and Fig 2. 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. Meter should indicate battery voltage. If battery voltage is present, go to next step. If voltage is not present, repair open in circuit No. 414 (Orange/Red wire).
  4. Turn air suspension switch off. Disconnect control module connectors. Measure resistance between circuit No. 421 (Pink wire) at compressor connector and pin No. 24 of control module connector. Meter should indicate less than 10 ohms. If 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 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 they are cycling ON and OFF. If valves cycle, go to step 10). If one or both valves are not cycling, DO NOT exit Functional Test 33. Go to next step.
  6. Disconnect inoperative spring solenoid connector. Measure voltage between both circuits in connector. Meter should pulse between zero volts and battery voltage. If meter pulses, replace inoperative spring solenoid. If no voltage pulses, exit Functional Test 33. Go to next step.
  7. Measure voltage between circuit No. 414 (Orange/Red wire) at spring solenoid connector and good ground. Meter should indicate battery voltage. If battery voltage is present, go to next step. If battery voltage is not present, repair open in circuit No. 414 (Orange/Red wire).
    Fig 2: Spring Solenoid Control Circuits
    G90F14311
  8. Turn air suspension switch to OFF position. Disconnect control module connectors. Measure resistance of spring solenoid control circuit between solenoid connector and Black control module connector. Meter should indicate less than 10 ohms. If resistance is less than 10 ohms, replace control module and both air spring solenoid valves. If resistance is 10 ohms or more, repair open in circuit between control module and solenoid valve connector.
    NOTE: Resistance measurements in the following procedure checks air spring solenoid valve coil and diode condition. A digital ohmmeter 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. Meter should indicate 15-18 ohms one way, and 5-10 ohms less the other way. See Figure. for terminal identification. If reading is 15-18 ohms and lower reading is 5-10 ohms more than higher reading, replace control module. Repeat SERVICE BAY DIAGNOSTICS under TESTING & DIAGNOSIS. If both readings are the same or 0-18 ohms, replace spring solenoid. Repeat SERVICE BAY DIAGNOSTICS under TESTING & DIAGNOSIS. Measure resistance between pins No. 25 and 1 on control module connectors. Reverse leads and measure resistance again between pins No. 25 and 1. Meter should indicate 15-18 ohms one way, and 5-10 ohms less the other way. See Figure. for terminal identification. If reading is 15-18 ohms and lower reading is 5-10 ohms below higher reading, replace solenoid. Repeat SERVICE BAY DIAGNOSTICS under TESTING & DIAGNOSIS. If both readings are within range, go to next step.
  10. Leave STAR 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 STAR 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.
  11. Disconnect air lines at both spring solenoid valves. Remove air spring solenoid heat shields, if equipped. Enter STAR tester Functional Test 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 Function Test 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.
  12. Lower vehicle. There should be nothing supporting vehicle. Measure distance between center of rear wheel opening lip and bottom of wheel (not bottom of tire). Measurement should be 24-25" (610-635 mm). This is vehicle riding height. If vehicle is higher, go to next step. If vehicle is lower, go to step 15).
  13. Remove air cleaner assembly and shield from compressor assembly. Disconnect air line at compressor drier. Enter STAR tester Function Test 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. Rear of vehicle may drop rapidly once Functional Test 23 is entered. If 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 airflow from air line and vehicle drops, exit Functional Test 23 before rear of vehicle becomes too low and go to next step.
  14. Remove drier from compressor. Connect air line to air drier. Enter Functional Test 23 (vent rear). See FUNCTIONAL TEST under TESTING & DIAGNOSIS. If little or no air flows through drier, replace air drier. Repeat SERVICE BAY DIAGNOSTICS under TESTING & DIAGNOSIS. If air flows through drier, replace air compressor assembly. Repeat SERVICE BAY DIAGNOSTICS under TESTING & DIAGNOSIS.
  15. Enter Functional Test 26 (compress rear). See FUNCTIONAL TEST under TESTING & DIAGNOSIS. Exit Functional Test 26 when rear of vehicle is raised about 2" (50 mm) above riding height. Distance should be about 26-27" (660-685 mm) from bottom of wheel (not bottom of tire) and center of rear wheel opening lip. If vehicle raises, go to step 13). If vehicle does not raise, but air compressor runs, exit Functional Test 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.
  16. Raise rear of vehicle and support on frame. Disconnect air line from air drier. Enter Functional Test 26 (compress rear). See FUNCTIONAL TEST under TESTING & DIAGNOSIS. Air should flow from air drier while compressor is running. If air flows from drier, repair blocked or kinked air line. If little or no airflow from drier, repeat Functional Test 26. Go to next step.
  17. Remove air drier from compressor. Enter Functional Test 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 little or no airflow from compressor, replace compressor assembly.
CAUTION: Enter Functional Test 26 (compress rear) and fill air springs for about 90 seconds before lowering rear of vehicle.
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