Engine Controls - System/Component Tests: Introduction

Before testing separate components or systems, perform procedures in BASIC TESTING article. Since many computer-controlled and monitored components set a trouble code if they malfunction, also perform procedures in TESTS W/CODES article.

NOTE: Testing individual components does not isolate shorts or opens. Perform all voltage tests with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure. Use ohmmeter to isolate wiring harness shorts or opens.

NOTE: For additional information on LS400 model, refer to TESTS W/CODES article. Refer to the following engine diagnostic charts:

NEUTRAL START SWITCH CIRCUIT chart.
ECU POWER SOURCE CIRCUIT chart.
BACK-UP POWER SOURCE CIRCUIT chart.
INJECTOR CIRCUIT chart.
COLD START INJECTOR CIRCUIT chart.
IDLE SPEED CONTROL (ISC) VALVE CIRCUIT chart.
FUEL SYSTEM CIRCUIT chart.
FUEL PRESSURE CONTROL VACUUM SWITCHING VALVE (VSV) CIRCUIT chart.
TERMINAL TE1 & TE2 CIRCUIT DIAGNOSIS chart.
A/C COMPRESSOR CIRCUIT chart.

Refer to the following transmission diagnostic charts:

MAIN THROTTLE POSITION SENSOR CIRCUIT chart.
NEUTRAL START SWITCH CIRCUIT chart.
STOPLIGHT CIRCUIT chart.
PATTERN SELECT SWITCH CIRCUIT chart.
O/D SWITCH & O/D OFF INDICATOR LIGHT CIRCUIT chart.
O/D CANCEL SIGNAL CIRCUIT chart.
DIAGNOSIS CIRCUIT chart.
CHECK CONNECTOR CIRCUIT chart.