System Operation Check

WARNING: This page is about a different car, the 2003 Lexus RX 300 and 2002 Lexus RX 300. However, it is still accessible from the selected car via links, so may be relevant.

Trouble shooting of a cruise control system complaint begins with verification of the customer problem. If problem occurs, go to step 3. If problem does not occur, go to next step.
If problem does not occur, review conditions under which problem occurred for customer and try to duplicate those conditions. For example, if the problem occurs on rainy days or during high humidity conditions, sprinkle water onto vehicle and see if malfunction occurs. DO NOT sprinkle water directly into engine compartment or onto electronic components. Visually inspect for signs of mechanical and electrical damage. Inspect for blown fuses and damaged relays. Inspect for loose or corroded connections, damaged wiring harness and/or switches. Check for a broken or partially broken wire inside insulation, which could cause system malfunction but prove good in a continuity/voltage check with system disconnected. Ensure any aftermarket electronic equipment is properly installed. If fault is found, repair as necessary.

Check the DTC. See RETRIEVING DIAGNOSTIC TROUBLE CODES under SELF-DIAGNOSTIC SYSTEM:

If there is a normal code, go to PROBLEM SYMPTOM INDEX table. Perform circuit inspection and input signal check, go to steps 4 and 5.
If there is a malfunction code, go to DIAGNOSTIC TROUBLE CODE INDEX table. Perform circuit inspection, go to step 4.

PROBLEM SYMPTOM INDEX

Symptom

Suspected Area ⁽¹⁾

SET Not Occurring Or CANCEL Occurring (DTC Is Normal)

⁽²⁾⁽³⁾⁽⁴⁾⁽⁵⁾⁽⁶⁾⁽⁷⁾⁽⁸⁾

SET Not Occurring Or CANCEL Occurring (DTC Does Not Output)

⁽⁹⁾⁽⁸⁾

Actual Vehicle Speed Deviates Above Or Below Set Speed

⁽⁷⁾⁽¹⁰⁾⁽¹¹⁾⁽⁶⁾⁽¹²⁾⁽⁸⁾

Gear Shifting Frequent Between 3rd & O/D When Driving On Uphill Road (Hurting)

⁽¹¹⁾⁽⁸⁾

Cruise Control Not Cancelled, Even When Brake Pedal Is Depressed

⁽⁷⁾⁽⁴⁾⁽⁶⁾⁽⁸⁾

Cruise Control Not Cancelled, Even When Transmission Is Shifted To N Position

⁽⁷⁾⁽⁵⁾⁽⁶⁾⁽⁸⁾

Control Switch Does Not Operate (SET/COAST, ACC/RES, CANCEL Not Possible)

⁽⁷⁾⁽⁶⁾⁽⁸⁾

SET Possible At 25 MPH (40 Km/h) Or Less, Or CANCEL Does Not Operate At 25 MPH (40 Km/h) Or Less

⁽⁷⁾⁽¹⁰⁾⁽⁶⁾⁽⁸⁾

Poor Response Is ACCEL & RESUME Modes

⁽⁷⁾⁽¹¹⁾⁽⁶⁾⁽⁸⁾

O/D Does Not Resume, Even Though Road Is Not Uphill

⁽¹¹⁾⁽⁸⁾

DTC Memory Is Erased

⁽⁸⁾

DTC Is Not Output, Or Is Output When It Should Not Be

⁽¹³⁾⁽⁸⁾

Cruise MAIN Indicator Light Remains ON Or Fails To Light Up

⁽¹⁴⁾

⁽¹⁾	Perform test procedures in order listed under suspected area.

⁽²⁾	Check the main switch circuit (cruise control switch). See CONTROL SWITCH CIRCUIT (CRUISE CONTROL SWITCH) under CIRCUIT TESTS.

⁽³⁾	Check the vehicle speed sensor circuit. See DTC 21: OPEN IN VEHICLE SPEED SENSOR CIRCUIT under DIAGNOSTIC TESTS.

⁽⁴⁾	Check the stop light switch circuit. See STOP LIGHT SWITCH CIRCUIT under CIRCUIT TESTS.

⁽⁵⁾	Check the park/neutral position switch circuit. See PARK/NEUTRAL POSITION SWITCH CIRCUIT under CIRCUIT TESTS.

⁽⁶⁾	Check the actuator motor circuit. See DTC 11, 15: ACTUATOR MOTOR CIRCUIT under DIAGNOSTIC TESTS.

⁽⁷⁾	Check the cruise control cable. See ACTUATOR CONTROL CABLE under COMPONENT TESTS.

⁽⁸⁾	Check the cruise control ECU.

⁽⁹⁾	Check the ECU power source circuit. See ECU POWER SOURCE CIRCUIT under CIRCUIT TESTS.

⁽¹⁰⁾	Vehicle speed signal is abnormal. See DTC 23: VEHICLE SPEED SIGNAL ABNORMAL under DIAGNOSTIC TESTS.

⁽¹¹⁾	Check the electronically controlled transmission circuit. See ELECTRONICALLY CONTROLLED TRANSMISSION COMMUNICATION CIRCUIT under CIRCUIT TESTS.

⁽¹²⁾	Check the idle signal circuit (main throttle position sensor). See DTC 51: IDLE SIGNAL CIRCUIT under CIRCUIT TESTS.

⁽¹³⁾	Diagnose circuit.

⁽¹⁴⁾	Check the cruise MAIN indicator light switch circuit. See CRUISE MAIN INDICATOR LIGHT CIRCUIT under CIRCUIT TESTS.

Inspect the cruise control circuits. See DIAGNOSTIC TESTS , CIRCUIT TESTS and COMPONENT TESTS .
Check the input signal. See INPUT SIGNAL CHECK under SELF-DIAGNOSTIC SYSTEM.
After problem has been identified and repaired, confirm repairs. See CONFIRMATION TEST under SELF-DIAGNOSTIC SYSTEM.