The on-board diagnosis function of the cruise control system uses Subaru Select Monitor.
The on-board diagnosis function operates in two categories, which are used depending on the type of problems;
1. Cruise Control Cancel Conditions Diagnosis:
(1) This category of diagnosis requires actual vehicle driving in order to determine the cause, as when cruise speed is cancelled during driving although cruise cancel condition is not entered.
(2) Cruise control memory in ECM stores the cancel condition (Code No.) which occurred during driving. When there are multiple cancel conditions (Code No.), they are shown on the Subaru Select Monitor.
CAUTION:
• The cruise control memory stores not only the cruise “cancel” which occurred (although “cancel” operation is not entered by the driver), but also the “cancel” condition input by the driver.
• The content of the latest memory (the latest code) is cleared when the ignition switch is turned to OFF. However, memory contents set by the diagnosis of faulty switches related to the system and cruise control will remain as trouble history (memory code) after the ignition switch is turned to OFF.
2. Real-time Diagnosis:
Real-time diagnosis function is used to determine whether or not the input signal system is in good order, according to signal emitted from switches, sensors, etc.
(1) Vehicle cannot be driven at cruise speed when the problem occurs in the cruise control system or relevant circuits.
(2) Monitor the signal conditions from switches and sensors.
2. CRUISE CONTROL CANCEL CONDITIONS DIAGNOSIS
1. Prepare the Subaru Select Monitor kit.
2. Connect the diagnosis cable to the Subaru Select Monitor.
3. Connect the Subaru Select Monitor to the data link connector.
(1) Data link connector is located in the lower portion of the instrument panel (on the driver’s side).
(2) Connect the diagnosis cable to the data link connector.
4. Start the engine and turn the cruise control main switch to ON.
5. Run the Subaru Select Monitor.
6. On the «Main Menu» display, select {2. Each System Check}.
On the system selection display screen, select the {Engine Control System} and select the [OK]. When engine name is displayed, select the [OK].
7. Drive vehicle at 40 km/h (25 MPH) or more and set the cruise control.
CAUTION:
• When performing diagnosis, observe the legal speed limit on the road.
• DTC will also appear when cruise cancel is effected by normal driving operation. Do not confuse them.
• Always get an assistant in the vehicle and have him/her operate the Select Monitor for help of diagnosis while driving.
8. If set speed is cancelled by itself (without canceling operation such as brake operation), or if cruise control could not be set even by the setting operation, select {Check Cancel Code} on the Engine Diagnosis screen. The DTC will then appear in the Select Monitor display.
NOTE:
There are {Latest Code} and {Memory Code} in DTC. The latest code recognized during current test drive is displayed in {Latest Code}. In addition, DTC set by the diagnosis of faulty switches related to the system and cruise control are also displayed in the {Memory Code}.
9. Perform the DTC memory clear operation for engine. 
DTC of the switches related to the system and cruise control will be cleared by the memory clear operation on the engine side.
NOTE:
The latest code will be cleared by turning ignition switch to OFF.
1. Connect the Subaru Select Monitor.
2. Turn the ignition switch and cruise control main switch to ON.
3. Run the Subaru Select Monitor.
4. On the «Main Menu» display, select {2. Each System Check}.
5. On the «System Selection Menu», select {Engine Control System}.
6. When engine name is displayed, select the [OK].
7. On the «Cruise Control Diagnosis» screen, select {Current Data Display & Save}.
8. Make sure that normal display is shown when operated as follows:
• Depress and release the brake pedal. (Stop light switch and brake switch are turned to ON.)
• Turn the main switch to ON.
• Turn the “CANCEL” switch to ON.
• Turn the “SET/COAST” switch to ON.
• Turn the “RESUME/ACCEL” switch to ON.
• Depress or release the clutch pedal.
• Place the shift lever in any position other than neutral.
NOTE:
• For details concerning the operation procedure, refer to the “SUBARU SELECT MONITOR OPERATION MANUAL”.
• Refer to “List of Diagnostic Trouble Code (DTC)” for DTC.