Trouble Shooting

WARNING: This page is about a different car, the 2000 Lexus SC 400, 2000 Lexus SC 300, 2000 Lexus LS 400, 2000 Lexus GS 400, and 2000 Lexus GS 300. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: If problem is intermittent, check for faulty wiring and components by wiggling wiring harnesses and components (DO NOT vigorously wiggle relays).

Check for Diagnostic Trouble Codes (DTCs). See RETRIEVING DIAGNOSTIC TROUBLE CODES under SELF-DIAGNOSTIC SYSTEM. If DTC(s) are set, perform appropriate procedure under DIAGNOSTIC TESTS . If no DTCs are set, go to SYMPTOM DIAGNOSIS table.
If ECM is suspected of not receiving an input from a switch or vehicle speed sensor, check input signal circuits. See INPUT SIGNAL CIRCUITS under CIRCUIT TESTS. If problem is still present after all testing, replace ECM.

SYMPTOM DIAGNOSIS

Problem

Inspect

Speed Cannot Be Set Or Unwanted Canceling

No DTCs Are Set (Normal DTC)

⁽¹⁾ Input Signal Circuit
⁽¹⁾ Vehicle Speed Sensor Circuit
⁽¹⁾ Stoplight Switch Circuit
⁽²⁾ Park/Neutral Position Switch Circuit
⁽³⁾ ECM

DTC Does Not Display

⁽³⁾ ECM

Actual Speed Differs From Set Speed

⁽¹⁾ Input Signal Circuit
⁽³⁾ ECM

Shifts Between 3rd Gear & Overdrive Uphill (Hurting)

⁽³⁾ ECM

Speed Setting Does Not Cancel

When Brake Pedal Is Pressed

⁽¹⁾ Stoplight Switch Circuit
⁽³⁾ ECM

When Shifting Into Neutral

⁽²⁾ Park/Neutral Position Switch Circuit
⁽³⁾ ECM

When Clutch Pedal Is Pressed

⁽³⁾ ECM

Cruise Control Switch Does Not Operate

⁽¹⁾ Input Signal Circuit
⁽³⁾ ECM

At Speeds Less Than 25 MPH, Speed Can Be Set Or CANCEL Does Not Operate

⁽¹⁾ Input Signal Circuit
⁽³⁾ ECM

Poor Response In ACC & RES

⁽³⁾ ECM

Overdrive Does Not RESUME

⁽³⁾ ECM

DTC

Memory Is Erased

⁽³⁾ ECM

Cannot Be Displayed Or Are Displayed When Should Not Be

Diagnostic Circuit
⁽³⁾ ECM

CRUISE Indicator Light Remains Illuminated Or Will Not Illuminate

⁽¹⁾ Input Signal Circuit
⁽³⁾ ECM

⁽¹⁾	Perform appropriate DTC test under DIAGNOSTIC TESTS . See DIAGNOSTIC TROUBLE CODE (DTC) DEFINITION table.

⁽²⁾	Perform DTC P1780 test in engine performance self-diagnostics. See appropriate SELF-DIAGNOSTICS article in ENGINE PERFORMANCE.

⁽³⁾	Perform ECM PIN VOLTAGE TESTS under COMPONENT TESTS.