1991 Lexus LS 400FACTORY OEM SERVICE PROCEDURE

Es250 Ground Circuits

  1. Ensure ignition is off. Disconnect connectors from ECU. Remove locks so ECU connectors can be easily backprobed. See Figure. Reconnect ECU connectors.
  2. Using an ohmmeter, check for continuity to ground on ECU terminals E1, E01 and E02. See Figure. Resistance should be zero ohms. If resistance is not zero ohms, repair open to ground.
  3. Using a DVOM, touch negative lead of voltmeter to a good ground. Touch positive lead of voltmeter to each ground terminal. With vehicle running, voltmeter should indicate less than one volt. If voltmeter reading is greater than one volt, check for open, corrosion and loose connection on ground lead.
NOTE: For testing LS400 power circuit, refer to ECU POWER SOURCE CIRCUIT, BACK-UP POWER SOURCE CIRCUIT and TERMINAL TE1 & TE2 CIRCUIT diagnosis charts at end of article. See CIRCUIT DIAGNOSIS CHARTS .
Factory Service Tools

Use the Manual With the Right Hardware

Pair factory procedures with proven DIY tools so the instructions are easier to execute.

Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.

Shop Manual-Ready ToolsCompare Repair QuoteQuote Shield Pro

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.

Rather have a pro handle this?

A certified mobile mechanic comes to your home or office. They bring the tools, you stay comfortable. No tow truck, no waiting room, no surprises.

Comes to youSame-day available12-month warranty
Get a Free Quote

No obligation. See pricing before you book.