1991 Lexus LS 400FACTORY OEM SERVICE PROCEDURE

Test Mode

  1. This mode detects same malfunctions as normal mode. It also detects malfunctions in starter signal circuit, No. 1 and No. 2 cam position sensors, idle contact signal of TPS, A/C signal and neutral start switch signal. Test mode is more sensitive to intermittent and regular faults. This mode is used for road test conditions.
  2. To read diagnostic codes, ensure battery voltage is at least 11 volts, throttle valve is fully closed, transmission is in Neutral and all accessories are off. Total Diagnostic Communication Link (TDCL) connector is located under left side of instrument panel. See Figure.
  3. Turn ignition off. Using a jumper wire, connect terminals E1 and TE2 together on TDCL connector. See Figure. Turn ignition on. DO NOT  start engine.
    NOTE: If terminals E1 and TE2 are connected after ignition is turned on, test mode will not start.
  4. When ignition is turned on, CHECK ENGINE light on instrument panel should flash. If CHECK ENGINE light does not flash, see TERMINAL TE1 & TE2 CIRCUIT DIAGNOSIS under CIRCUIT DIAGNOSIS CHARTS in I - SYS/COMP TESTS article in this section.
  5. Start engine. Perform road test and simulate conditions described by customer. DO NOT  disconnect jumper wire connecting terminals E1 and TE2. After road test, connect terminals E1 and TE1 together on TDCL connector using a jumper wire.
  6. Count number of flashes from CHECK ENGINE light. System is normal if CHECK ENGINE light flashes 2 times every second. If a diagnostic code is displayed, first group of flashes will indicate first digit of a 2-digit diagnostic code. After a 1.5 second delay, second group of flashes will indicate second digit of diagnostic code.
  7. If more than one code is stored, a 2.5 second delay will occur between diagnostic codes. After all diagnostic codes have been displayed, a 4.5 second delay will occur, and then diagnostic codes will be repeated until jumper wire connecting terminals E1 and TE1 is disconnected. Diagnostic codes will display from smallest to largest number.
  8. After completing check, disconnect terminals TE1 and TE2 from terminal E1 on TDCL connector. Diagnostic Codes 17, 18 and 43 will set if engine is not cranked when entering test mode. This is normal. If automatic transmission is in D, 2, L or R, A/C switch is in ON position or accelerator pedal is depressed, Code 51 will set. This is normal.
  9. Record diagnostic codes. See DIAGNOSTIC CODE IDENTIFICATION  table for identification. After reading description of diagnostic code, see appropriate diagnostic code chart. To clear codes, see CLEARING CODES.
Factory Service Tools

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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.

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