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.
1991 Lexus LS 400FACTORY OEM SERVICE PROCEDURE
Engine Controls - Tests W/Codes
- Introduction
- Self-Diagnostic System
- Summary
- Diagnostic Code Charts
- Notes
- Code 12: Engine Speed Sensor
- Code 13: Rpm Signal Circuit No. 2
- Code 14 & 15: Ignition Signal No. 1 & 2
- Code 16: Elect Controlled Trans (ECT) Control Signal
- Code 21 & 28: Left Or Right Bank Main O2 Sensor Signal
- Code 22: Water Temperature Sensor Signal
- Code 24: Intake Air Temperature Sensor Signal
- Code 25 & 26: Air/Fuel Ratio Lean Or Rich
- Codes 27 & 29: Left Bank O2 Sensor Signal
- Code 31: Airflow Meter Signal
- Code 35: High Altitude COMPENSATOR (HAC) Sensor Signal
- Codes 41 & 47: Throttle Position Sensor (TPS) Signal
- Code 43: Starter Signal
- Code 51: Switch Condition Signal
- CODE 52, 53 & 55: No. 1 & 2 KNOCK SENSOR & CONTROL SIGNAL
- Code 71: EGR System Malfunction (CALIF)
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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