Diagnostic Starting Point - Automatic Level Control
Begin the system diagnosis with the Diagnostic System Check - Automatic Level Control . You may want to review the Automatic Level Control Description and Operation before beginning the diagnosis. The Diagnostic System Check will provide the following information
- The identification of the control modules which command the system
- The ability of the control modules to communicate through the serial data circuit
- The identification of any stored diagnostic trouble codes (DTCs) and their status
The use of the Diagnostic System Check will identify the correct procedure for diagnosing the system and where the procedure is located.
Scan Tool Output Controls
| Scan Tool Output Control | Additional Menu Selection(s) | Description |
|---|---|---|
| Compressor Test | Commands the air compressor ON and OFF. | |
| Exhaust Solenoid | Commands the air compressor exhaust solenoid ON and OFF. | |
| Recalibration | Performs calibration on the suspension control module. |
Scan Tool Output Controls
Scan Tool Data List
| Scan Tool Parameter | Data List | Units Displayed | Typical Data Value |
|---|---|---|---|
| Operating Conditions: Park brake set with ignition switch ON | |||
| Compressor Signal | Data Display | ON/OFF | OFF |
| Controller Battery Volts | Data Display | Volts | 12-14.7 |
| Exhaust Signal | Data Display | ON/OFF | OFF |
| Left Rear Position Sensor | Data Display | Volts | 0.5-4.85 |
| Rear Leveling Air Press | Data Display | Psi/kpa | 16.0-187.8 |
| Rear Leveling Air Press | Data Display | Volts | 0.15-4.85 |
| Right Rear Position Sensor | Data Display | Volts | 0.5-4.85 |
| Sensor Supply Voltage | Data Display | Volts | 4.85 |
| Vehicle Speed | Data Display | Mph/kmph | 0 |
Scan Tool Data List
Diagnostic Trouble Code (DTC) List
Note. General Motors has issued a TSB concerning DTC C0580. See TSB 03-03-11-001 .
| DTC | Module(s) |
|---|---|
| C0655 | RTD |
| C0660 | RTD |
| C0711 | RTD |
Diagnostic Trouble Code (DTC) List
Circuit Description
The vehicle's rear leveling compressor motor is switched on and off via a compressor motor relay which is controlled by the Suspension Control module. The Suspension Control module provides a switched path to ground whenever compressor activity is required. The Suspension Control module continually monitors the compressor motor relay circuitry to determine if the voltage level agrees with the commanded state.
Conditions for Running the DTC
Whenever the compressor is activated.
Conditions for Setting the DTC
- Open in the control circuit of the compressor motor relay.
- Short to ground in the control circuit of the compressor motor relay.
- Short to battery in the control circuit of the compressor motor relay.
- Open in the ignition 3 voltage circuit of the compressor motor relay.
- Open IGN 3 fuse.
- A malfunctioning compressor motor relay.
Action Taken When the DTC Sets
- The compressor motor relay is disabled for the remainder of the ignition cycle.
- Stores a DTC C0655 in the Suspension Control module memory.
Conditions for Clearing the DTC
- The Suspension Control module no longer detects a open, short to ground, or a short to battery in the control circuit of the compressor motor relay.
- Using a scan tool.
- A history DTC will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.
Diagnostic Aids
| IMPORTANT | A leak in the air tube between the rear shocks and compressor will cause excessive running of the compressor motor. After approximately 5 minutes of continuous running without a change in body-to-wheel height or system pressure, the Suspension Control module will command the compressor motor relay to the off state for the remainder of the ignition cycle. |
The following conditions may cause a malfunction to occur in the compressor motor relay
- A short to ground in the control circuit.
- An open in the control circuit.
- A short to battery in the control circuit.
- An open in the ignition 3 voltage circuit.
The exhaust solenoid valve is switched on and off via the Suspension Control module. The Suspension Control module provides a switched path to ground whenever exhaust activity is required and during a compressor "head-relief" sequence which occurs at compressor start-up if system pressure is lower than 68.95 kPa (10 psi). The Suspension Control module continually monitors the exhaust solenoid valve circuitry to determine if the voltage level agrees with the commanded state.
Whenever the exhaust solenoid valve is activated.
- An open in the control circuit of the exhaust solenoid valve.
- A short to ground in the control circuit of the exhaust solenoid valve.
- A short to battery in the control circuit of the exhaust solenoid valve.
- An open in the battery positive voltage circuit of the exhaust solenoid valve.
- An open RTD fuse.
- A malfunctioning exhaust solenoid valve.
- The exhaust solenoid valve is disabled for the remainder of the ignition cycle.
- Stores a DTC C0660 in the Suspension Control module memory.
- The Suspension Control module no longer detects a open, short to ground, or a short to battery in the control circuit of the exhaust solenoid valve.
- Using a scan tool.
- A history DTC will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.
The following conditions may cause a malfunction to occur in the exhaust solenoid valve
- A short to ground in the control circuit.
- An open in the control circuit.
- A short to battery in the control circuit.
- An open in the battery positive voltage circuit.
The suspension control module uses a 5 volt analog air pressure sensor to determine the amount of air pressure in the Automatic Level Control (ALC ) system. The valid signal voltage range of the sensor is 0.15-4.85 volts. The sensor signal voltage will increase and decrease within the valid voltage range as system pressure increases and decreases.
The Ignition is ON.
- The air pressure sensor's signal voltage is out of the valid range.
- A short to ground, short to voltage, or an open in the pressure sensor, or the circuits to the sensor.
- DTC C0711 is stored in memory.
- ALC system pressure is set to a default value.
- The ALC system is disabled.
- A current DTC will clear when the malfunction is no longer present.
- A history DTC will clear after 100 malfunction free ignition cycles.
- Using a scan tool.
If DTC C0870 is present, perform the diagnosis for that DTC first.
The following conditions may cause a malfunction to occur
- An open in the 5 volt reference circuit of the air pressure sensor.
- A short to ground in the 5 volt reference circuit of the air pressure sensor.
- An open in the signal circuit of the air pressure sensor.
- A short to ground in the signal circuit of the air pressure sensor.
- An open in the low reference circuit of the air pressure sensor.
- A malfunction in the air pressure sensor.
- A leak in the air tube at the air pressure sensor may cause a faulty sensor voltage reading.
Visual/Physical Inspection
- Inspect for aftermarket devices which could affect the operation of the Automatic Level Control System. Refer to «CHECKING AFTERMARKET ACCESSORIES»(ref-175720-S08180388062005042600000) in Wiring Systems.
- Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.
- Inspect the connectors to be properly seated and free of corrosion.
Symptom List
Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom
- «Automatic Level Control Compressor Motor Always On»(ref-186288-S17195930792005083000000)
- «Automatic Level Control Compressor Motor Inoperative»(ref-186288-S03963871362005083000000)