Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSLEXUS1998GS 300REPAIR AND DIAGNOSISENGINE PERFORMANCESYSTEMENGINE CONTROLS - TESTS W/CODESSELF-DIAGNOSTIC SYSTEMTEST PREPARATION
1998 Lexus GS 300
Test Preparation
1998 Lexus GS 300SECTION Test Preparation
- Manufacturer recommends using Check Harness "A" (SST 09990-01000) when using circuit tests to diagnose malfunctions. Check harness "A" is a test harness that is installed between Electronic Control Module (ECM) and ECM connectors. See Fig 1. Voltage and resistance readings are taken at check harness connectors.NOTE: Always check and note diagnostic trouble codes prior to disconnecting ECM connector. Disconnecting ECM connector will erase codes from memory.
- To install check harness "A", ensure ignition switch is in the OFF position. Disconnect ECM connector. ECM is located behind glove box.
- Connect check harness "A" between ECM and ECM connector. Terminal arrangement of check connector is the same as those on the ECM. Wire colors that are specified in procedures apply to ECM connectors, but may not apply to check harness connectors. Proceed to appropriate circuit test.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.