How to Read & Clear Diagnostic Trouble Codes
1990-1994 Lexus LS400
Check engine light on? O/D OFF light blink periodicly? This tutorial will show you how to read the codes for the engine, transmission, airbag, ABS and TRAC systems and how to clear them. Checking for any codes is the first step is diagnosing problems and so everyone should know how to do this. It's simple and will only take you a few minutes. Please do not contact me regarding a specific code you have. The only thing I can tell you is to follow the diagnostic procedure in the repair manual, or you can search on the forums listed on the links page.
If you have a 1990-1994 LS then you have an OBDI system (On-board diagnostics I). This system is what I will cover here.
If you have a 1995 LS on up then you have an OBDII system. Reading codes from these systems requires you to use an OBDII code reader. They typically run around $100. They're not cheap but they can provide many more codes and this makes diagnosis easier. All you need to do is plug the scan tool into the diagnostic port and it displays any codes.
Tools Needed:- Short piece of wire (90-94 LS's)
- OBDII code reader (95+ LS's)
1) In order to read the code the battery must be 11v or higher, throttle valve fully closed, transmission in neutral position, and AC turned off. For checking transmission codes the OD switch must in on (pushed in). Connect terminals Te1 and E1 by placing a short piece of wire in the TDCL diagnostic port under the steering wheel. You can also connect these terminals using the check connector located in the engine bay. For engine and transmission codes you place the jumper wire in Te1 and E1. For air bag codes, ABS and TRAC codes, you place the jumper wire in Tc and E1.
2) Turn the ignition switch on. The diagnostic code is read by counting the number of blinks on the appropriate light. For engine codes, you count the blinks on the check engine light. For transmission codes, you count the blinks on the "O/D OFF" light. For airbag codes, you count the blinks on the "airbag" light. For ABS codes, you count the blinks on the "ANTILOCK" light. For TRAC codes, you count the blinks on the "TRAC" light. The codes are all two digits, the first digit is output first, it will pause 1.5 seconds and then output the second digit outputs. Multiple codes can be output. In this case the lowest numbered code is output first followed by a 2.5 second pause between other higher numbered codes in increasing numerical order. Once all stored codes have been output there will be a 4.5 second pause and then the codes repeat. If there are no codes stored then the light will blink continuously, every .25 second. I know this sounds a little confusing but it's very simple once you do it or see an example yourself....
Click here to see a video of engine code 71 (2.5 MB), single code output.
Click here to see a video of transmission codes 63 & 67 (2.9 MB), multiple codes output.
3) Once repairs have been made, clear all stored codes by removing the 20 amp EFI fuse shown above for 10 seconds or more with the ignition switch off. You can also clear codes by removing the negative lead on the battery for the same amount of time, but you'll lose all your clock, radio, and memory settings. After you've cleared the codes go for a road test. If the codes reappear it means you haven't fixed the problem. Note: airbag code 41 cannot be cleared using this method, here's how to clear it. ABS & TRAC codes are cleared by keeping the jumper wire in Tc and E1 and then pressing the brake pedal 8 or more times within 3 seconds.
Engine OBDI Diagnostic Codes
The list below will tell you where the problem lies but will not go into diagnosis. Please consult your repair manual for in depth diagnosis, testing and troubleshooting.
12 - RPM signal no. 1
13 - RPM signal no. 2
14 - Ignition no. 1 signal
15 - Ignition no. 2 signal
16 - ECT control signal
17 - No. 1 cam position sensor signal
18 - No. 2 cam position sensor signal
21 - Main oxygen sensor signal (on left bank)
22 - Water temp sensor signal
24 - Intake air temp. sensor signal
25 - Air-fuel ratio lean malfunction
26 - Air-fuel ratio rich malfunction
27 - Sub-oxygen sensor signal (on left bank)
28 - Main oxygen sensor signal (on right bank)
29 - Sub-oxygen sensor signal (on right bank)
31 - Air flow meter signal
35 - HAC sensor signal
41 - Throttle position sensor signal
43 - Starter signal
47 - Sub-throttle position sensor signal
51 - Switch condition signal
52 - No. 1 knock sensor signal
53 - Knock control signal
55 - No. 2 knock sensor signal
71 - EGR system malfunction
Transmission OBDI Diagnostic Codes
42 - No. 1 speed sensor signal malfunction
46 - Open or short circuit in no. 4 solenoid valve
61 - No. 2 speed sensor signal malfunction
62 - Open or short circuit in no. 1 solenoid valve
63 - Open or short circuit in no. 2 solenoid valve
64 - Open or short circuit in no. 3 solenoid valve
67 - OD direct clutch speed sensor signal malfunction
68 - Short circuit in kick-down switch
Air Bag OBDI Diagnostic Codes
11 - Short in squib circuit or front airbag sensor circuit (to ground)
12 - Short in squib circuit or front airbag sensor circuit (to +B)
13 - Short in squib circuit (between D+ wire harness and D- wire harness)
14 - Open in squib circuit
15 - Open in front airbag sensor sensor circuit
22 - Airbag warning light system
31 - Center airbag sensor assembly malfunction
41 - Malfunction stored in memory
ABS OBDI Diagnostic Codes
11 - Open circuit in ABS solenoid relay circuit
12 - Short circuit in ABS solenoid relay circuit
13 - Open circuit in pump motor relay circuit
14 - Short circuit in pump motor relay circuit
21 - Open or short circuit in 3-position solenoid circuit for front right wheel
22 - Open or short circuit in 3-position solenoid circuit for front left wheel
23 - Open or short circuit in 3-position solenoid circuit for rear right wheel
24 - Open or short circuit in 3-position solenoid circuit for rear left wheel
31 - Front right wheel speed sensor signal malfunction
32 - Front left wheel speed sensor signal malfunction
33 - Rear right wheel speed sensor signal malfunction
34 - Rear left wheel speed sensor signal malfunction
35 - Open circuit in front left or rear right speed sensor circuit
36 - Open circuit in front right or rear left speed sensor circuit
37 - Faulty front speed sensor rotor
41 - Low battery voltage or abnormally high battery voltage
43 - Malfunction in TRAC control system
51 - Pump motor is locked, Open in pump motor ground
Always ON - Malfunction in ECU
TRAC OBDI Diagnostic Codes
11 - Open in TRAC brake main relay circuit
12 - Short in TRAC brake main relay circuit
13 - Open in TRAC throttle relay circuit
14 - Short in TRAC throttle relay circuit
15 - Electric supply to TRAC motor for a long time (fluid leakage)
16 - Open circuit in pressure switch circuit
17 - Pressure switch remains OFF
19 - TRAC motor ON and OFF operation is higher than a predetermined number of times (accumulator pressure leakage)
21 - Open or short in master cylinder cut solenoid valve circuit
22 - Open or short in accumulator cut solenoid valve circuit
23 - Open or short in reservoir cut solenoid valve circuit
24 - Open or short in sub-throttle actuator circuit
25 - Step motor does not move to a position decided by ECU
26 - Sub-throttle valve does not move even when the sub-throttle valve is controlled to fully open position by ECU
27 - When power supply to step motor is stopped, sub-throttle valve does not reach its fully-open position
44 - During TRAC control, NE signals are not input to the ECU
45 - When idle switch is ON, main throttle position sensor signal is 1.5V or higher
46 - Main throttle position sensor signal is 4.3V or higher, or main throttle position sensor signal is 0.2V or lower when idle switch is OFF
47 - When idle switch is ON, sub-throttle position sensor signal is 1.45V or higher
48 - Sub-throttle position sensor signal is 4.3V or higher, or sub-throttle position sensor signal is 0.2V or lower when idle switch is OFF
49 - Open or short in engine communication circuit
51 - Problem in engine control system
52 - Brake fluid level warning switch ON
54 - Open in TRAC motor relay circuit
55 - Short in TRAC motor relay circuit
56 - TRAC pump motor locked
Always ON - Malfunction in ECU
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