1994 Lexus SC 400FACTORY OEM SERVICE PROCEDURE

Trouble Code Identification

TROUBLE CODE IDENTIFICATION

Code System Affected (1) MIL In Normal Mode (1) MIL In Test Mode Probable Cause
12  RPM Signal ON N/A Camshaft Position Sensor, Starter Or Circuit, ECM
13  RPM Signal (2) (3) Camshaft Position Sensor Or Circuit ECM
14  Ignition Signal ON N/A Ignitor Or IGF1 Circuit To ECM, ECM
15  Ignition Signal ON N/A Ignitor Or IGF2 Circuit To ECM, ECM
16 (4) A/T Control Signal ON N/A ECM Or Circuit
21  O2 Sensor Signal ON ON O2 Sensor (Left Bank) Or Circuit, ECM
22  Engine Coolant Temp. Sensor Signal ON ON Engine Coolant Temperature Sensor Or Circuit, ECM
24  Intake Air Temp. Signal ON ON Intake Air Temperature Sensor Or Circuit, ECM
25  Lean Air/ Fuel Mixture ON ON Injector Or Ckt., O2 Sensor Or Ckt. Fuel Pressure, Ignition System, Vacuum Leak, Compression Pressure, ECM
26  Rich Air/ Fuel Mixture ON ON Injector Or Ckt., O2 Sensor Or Ckt. Fuel Pressure, Ignition System, Compression Pressure, ECM
27  Sub-O2 Sensor Signal ON ON Sub-O2 Sensor (Left Bank) Or Circuit, ECM
28  O2 Sensor Signal ON ON O2 Sensor (Right Bank) Or Circuit, ECM
29  Sub-O2 Sensor Signal ON ON Sub-O2 Sensor (Right Bank) Or Circuit, ECM
31  Airflow Meter ON N/A Airflow Meter Or Ckt., ECM
35  BARO Sensor ON ON ECM
41  Throttle Position Sensor Signal ON ON Throttle Position Sensor Or Circuit, ECM
42  Vehicle Sensor Signal OFF OFF Vehicle Speed Sensor Or Circuit, ECM
43  Starter Signal N/A OFF Starter Signal Circuit, Starter Relay, Ignition Sw. Or Circuit, ECM
47  Sub-Throttle Position Sensor Signal OFF ON Sub-Throttle Position Sensor Or Circuit, ECM
51  Switch Condition Signal N/A OFF A/C Switch Circuit, Park/Neutral Switch Or Circuit, TPS Or Circuit, ECM
52 (5) Knock Sensor Signal ON N/A Knock Sensor Or Or Circuit, ECM
53  Knock Control Signal ON N/A ECM
55 (6) Knock Sensor Signal ON N/A Rear Knock Sensor Or Or Circuit, ECM
71  EGR System Malfunc. ON ON EGR System, EGR Temperature Sensor Or Circuit EGR-VSV, ECM
78  Fuel Pump Control Signal OFF ON Fuel Pump ECU Or Ckt., Fuel Pump, ECM Power Source Or ECM
(1) ON indicates MIL on instrument panel will be illuminated. N/A indicates item is not included in malfunction diagnosis when using this mode. OFF indicates MIL on instrument panel will not be illuminated even if malfunction is detected.
(2) The MIL will be illuminated only if no "NE" signal is sent to ECM with engine at approximately 1000 RPM.
(3) The MIL will be illuminated only if "NE" signal does not pulse 12 times to ECM during interval between "G1" and "G2" pulses.
(4) Applies only to models with electronic controlled automatic transmission.
(5) Front knock sensor may be referred to as No. 1 knock sensor.
(6) Rear knock sensor may be referred to as No. 2 knock sensor.
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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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