Circuit Description
The ALC exhaust solenoid valve is controlled (switched ON or OFF) by the CVRSS control module. The control module provides a low-side drive (switched to ground) whenever exhaust activity is required and during a head-relief sequence which occurs before each compressor start-up. This drive output from the CVRSS control module is continually monitored to determine if the voltage level agrees with the commanded state.
Conditions for Setting the DTC
The DTC will set when the CVRSS control module measures a feedback voltage condition at pin C14 less than a preset threshold during an exhaust solenoid valve OFF-state.
The DTC will turn history when the CVRSS control module no longer senses a low voltage condition at pin C14 when the exhaust solenoid valve is in an OFF-state.
Action Taken When the DTC Sets
| • | ALL rear leveling activity for the remainder of the ignition cycle will be disabled. |
| • | The SERVICE RIDE CONTROL message will be displayed. |
Conditions for Clearing the MIL/DTC
| • | Use the scan tool. |
| • | Use the On-Board diagnostic CLEAR RSS CODES feature. |
Diagnostic Aids
A temporary compressor overload (i.e., high head pressure during a cold start) may cause the Electronic Suspension Control Maxi circuit breaker to trip. This is one possible cause of DTC C1738.
A DTC C1738 fault condition is detectable only when the exhaust solenoid valve output is commanded to the OFF-state, which occurs whenever exhaust activity is not required. The CVRSS control module expects to see a high voltage condition during the OFF-state.
Only electrical problems with the exhaust solenoid valve are flagged. Pneumatic blockage problems do not set a DTC, but the CVRSS control module shuts off the exhaust function if no progress is made, or if excessive run time occurs. Recovery is not attempted until the ignition is cycled OFF and ON.
Check for disconnected or damaged air lines. Replace or reconnect the air lines as needed.
Test Description
Important:
• Do not backprobe the sensors, actuators, or any sealed connectors. • When all the diagnostics and repairs are complete, clear the DTCs
and verify the operation.
The number(s) below refer to the step number(s) on the diagnostic table.
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This step checks to see if the Electronic Suspension Control circuit breaker is tripped.
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This step checks for an open circuit condition in CKT 1340.
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This step checks for an internal open circuit condition in the exhaust solenoid valve.
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This step checks for a short circuit to ground condition in CKT 320.
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This step checks for an open circuit condition in CKT 320.
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This step checks for an internal short circuit condition in the exhaust solenoid valve.
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This step checks for a short circuit to ground condition in CKTs 1340 and 322.
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This step checks for a short circuit to ground condition in the compressor assembly pigtail or internally to the compressor assembly.
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the CVRSS System Check performed? | -- | Go to Step 2 | |||||||||
Is the measurement greater than the specified value? | 10 V | Go to Step 3 | Go to Step 9 | |||||||||
Is the measurement greater than the specified value? | 10 V | Go to Step 4 | Go to Step 16 | |||||||||
Measure the resistance between pin C and pin A of the ALC compressor assembly connector (compressor assembly side). Is the measurement within the specified values? | 25-35 ohms | Go to Step 5 | Go to Step 17 | |||||||||
Was a short circuit to ground condition found? | -- | Go to Step 6 | Go to Step 7 | |||||||||
6 | Repair the short circuit to ground condition in CKT 320. Is the repair complete? | -- | Go to Step 18 | -- | ||||||||
Check for an open circuit condition or poor connection condition in CKT 320. Was an open circuit condition or a poor connection condition found? | -- | Go to Step 8 | Go to Step 13 | |||||||||
8 | Repair the open circuit condition or the poor connection condition in CKT 320. Is the repair complete? | -- | -- | |||||||||
Is the measurement within the specified values? | 25-35 ohms | Go to Step 10 | Go to Step 17 | |||||||||
Check for a short circuit condition (continuity) between CKT 1340 and ground, and between CKT 322 and ground. Was a short circuit to ground condition found? | -- | Go to Step 11 | Go to Step 12 | |||||||||
11 | Repair the short circuit to ground condition in CKT 1340 or CKT 322. Is the repair complete? | -- | Go to Step 18 | -- | ||||||||
12 | Measure the resistance between the following pins of the compressor assembly connector (compressor assembly side):
Is the measurement less than the specified value? | 5 ohms | Go to Step 17 | Go to Step 14 | ||||||||
13 |
Is DTC C1738 set? | -- | Go to Step 20 | |||||||||
Check for intermittent short circuit to ground conditions on CKTs 322, 1340 and within the compressor assembly pigtail. Refer to Intermittents and Poor Connections . Was an intermittent short circuit to ground condition found? | -- | Go to Step 15 | ||||||||||
15 | Repair the short circuit to ground condition. Is the repair complete? | -- | Go to Step 18 | -- | ||||||||
16 | Repair the open circuit condition in CKT 1340. Is the repair complete? | -- | -- | |||||||||
17 |
Are the replacements complete? | -- | Go to Step 18 | -- | ||||||||
18 | Check the Electronic Suspension Control Maxi circuit breaker for valid operation. Is the circuit breaker operating properly? | -- | Go to Step 19 | |||||||||
19 | Replace the Electronic Suspension Control Maxi circuit breaker. Is the replacement complete? | -- | -- | |||||||||
20 |
Important: The controller must be calibrated. Is the CVRSS control module calibrated? | -- | -- |
