Trouble Shooting

WARNING: This page is about a different car, the 2002 Lexus GS 430 and 2002 Lexus GS 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 harnesses 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 a malfunction code is retrieved, go to DIAGNOSTIC TROUBLE CODE INDEX table. Perform circuit inspection, go to step 4.

If a normal code is retrieved, go to PROBLEM SYMPTOM INDEX table. Perform circuit inspection and input signal check, go to steps 4 and 5 .

PROBLEM SYMPTOM INDEX

Symptom

Suspected Area ⁽¹⁾

SET Not Occurring Or CANCEL Occurring (DTC Normal)

⁽²⁾⁽³⁾⁽⁴⁾⁽⁵⁾⁽⁶⁾

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

⁽⁶⁾

Actual Vehicle Speed Deviates Above Or Below The Set Speed

⁽²⁾⁽⁶⁾

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

⁽⁶⁾

Cruise Control Not Cancelled, Even When Brake Pedal Is Depressed

⁽⁴⁾⁽⁶⁾

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

⁽⁵⁾⁽⁶⁾

Cruise Control Not Cancelled, Even When Clutch Pedal Is Depressed

⁽⁶⁾

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

⁽²⁾⁽⁶⁾

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

⁽²⁾⁽⁶⁾

Poor Response Is ACCEL & RESUME Modes

⁽⁶⁾

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

⁽⁶⁾

DTC Memory Is Erased

⁽⁶⁾

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

⁽⁷⁾⁽⁶⁾

Cruise MAIN Indicator Light Remains ON Or Fails To Light Up

⁽²⁾⁽⁶⁾

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

⁽²⁾	Check the input signal circuit. See DTC P1566/54: INPUT SIGNAL CIRCUIT under DIAGNOSTIC TESTS.

⁽³⁾	Check the vehicle speed sensor circuit. See DTC P0500/21, 23: VEHICLE SPEED SIGNAL ABNORMAL under DIAGNOSTIC TESTS.

⁽⁴⁾	Check the stop light switch circuit. See DTC P1520/52: SHORT IN STOP LIGHT SWITCH CIRCUIT under DIAGNOSTIC TESTS.

⁽⁵⁾	Check the park/neutral position switch circuit. See DTC P1780: PARK/NEUTRAL POSITION SWITCH MALFUNCTION under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - GS300 article or SELF-DIAGNOSTICS - GS430 article under FAULT ISOLATION in ENGINE PERFORMANCE.

⁽⁶⁾	Check the ECM. See PIN VOLTAGE TESTS .

⁽⁷⁾	Diagnosis the circuit. See CRUISE CONTROL in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.

Perform an inspection of the cruise control circuits. See DIAGNOSTIC TESTS and CIRCUIT 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.