1991 Lexus LS 400FACTORY OEM SERVICE PROCEDURE

Sensor Operating Specifications

NOTE: All voltage tests should be performed with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure.
AIRFLOW METER RESISTANCE TEST

Terminals Ohms °F (°C)
ES250
VS & E2 200-600 N/A
VC & E2 200-400 N/A
THA & E2 10,000-20,000 -4 (-20)
THA & E2 4000-7000 32 (0)
THA & E2 2000-3000 68 (20)
THA & E2 900-1300 104 (40)
THA & E2 400-700 140 (60)
FC & E1 Infinity N/A
LS400
THA & E2 10,000-20,000 -4 (-20)
THA & E2 4000-7000 32 (0)
THA & E2 2000-3000 68 (20)
THA & E2 900-1300 104 (40)
THA & E2 400-700 140 (60)
ES250 AIRFLOW METER MEASURING PLATE RESISTANCE TEST

Terminals Ohms Measuring Plate Position Position
FC & E1 Infinity Fully Closed
FC & E1 Zero Other Than Closed
VS & E2 200-600 Fully Closed
VS & E2 (1) 20-1000 Fully Open
(1) Resistance will change in a wave pattern as measuring plate is opened.
COLD START INJECTOR TIME SWITCH RESISTANCE TEST

Terminals Ohms °F (°C)
STA & STJ 25-45 Less Than 59 (15)
STA & STJ 65-85 More Than 86 (30)
STA & Ground 25-85 N/A
COOLANT TEMPERATURE SENSOR RESISTANCE TEST

Temperature Ohms
4°F (20°C) 10,000-20,000
32°F (0°C) 4000-7000
68°F (20°C) 2000-3000
104°F (40°C) 900-1300
140°F (60°C) 400-700
176°F (80°C) 200-400
EGR GAS TEMPERATURE SENSOR RESISTANCE TEST (1)

Sensor Temperature Ohms
122°F (50°C) 69,400-88,500
212°F (100°C) 11,890-14,370
302°F (150°C) 2790-3590
(1) Measure between sensor terminals with sensor connector disconnected.
INTAKE AIR TEMPERATURE SENSOR RESISTANCE TEST (1)

Terminals Ohms °F (°C)
ES250: THA & E2 2000-3000 68 (20)
LS400: THA & E2 200-300 68 (20)
(1) Measure resistance with ECU connector connected.
ISC VALVE RESISTANCE TEST

Terminals Ohms
B1 & S1 Or S3 10-30
B2 & S2 Or S4 10-30
MAIN OXYGEN SENSOR HEATER RESISTANCE TEST (1)

Sensor Temperature Ohms
68°F (20°C) 5.1-6.3
(1) Measure resistance between terminals +B and HT of oxygen sensor 4-pin connector.
TPS SPECIFICATIONS RESISTANCE TEST

TPS Terminals Conditions Ohms
ES250
VTA & E2 (1) Zero 300-6300
IDL & E2 (1) .012" (.30 mm) 2300 or less
IDL & E2 (1) .028" (.71 mm) Infinity
VTA & E2 Throttle Valve Fully Open 350-10,300
VC & E2 N/A 4250-8250
LS400
VTA & E2 (1) Zero 200-1200
IDL & E2 (1) .0157" (.40 mm) 2300 or less
IDL & E2 (1) .0335" (.85 mm) Infinity
VTA & E2 Throttle Valve Fully Open 3300-10,000
VC & E2 N/A 4000-9000
(1) Clearance between throttle lever and stop screw.
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.