Engine Controls - Tests W/codes — Lexus LS I (1989-1994)

INTRODUCTION

If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed with self-diagnostics. If no fault codes or only pass codes are present after entering self-diagnostics, proceed to TESTS W/O CODES article in this section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.).

HARD FAILURES

Hard failures cause malfunction light to illuminate and remain on until problem is repaired. If light comes on and remains on (light may flash) during vehicle operation, cause of malfunction must be determined using diagnostic (code) charts. If a sensor fails, control unit will use a substitute value in its calculations to continue engine operation. In this condition, commonly known as limp-in mode, the vehicle runs but driveability will not be optimum.

INTERMITTENT FAILURES

Intermittent failures may cause CHECK ENGINE light to flicker or illuminate and go out after the intermittent fault goes away. However, the corresponding trouble code will be retained in ECU memory (except for Codes 16, 17, 18, 43, 51 and 53). Codes 16, 17, 18, 43, 51 and 53 do not illuminate CHECK ENGINE light and are output only during test procedures. See appropriate diagnostic code chart.

Codes must be erased from memory after repair has been made. Intermittent failures may be caused by sensor, connector or wiring related problems. See INTERMITTENTS in TESTS W/O CODES article in this section.

Scheme 62

Scheme 62: Normal Mode

Scheme 63

Scheme 64

Normal mode is used for routine testing of vehicle. To read diagnostic codes, ensure battery voltage is at least 11 volts, throttle valve is fully closed, transaxle/transmission is in Neutral and all accessories are off.
Total Diagnostic Communication Link (TDCL) connector is located under left side of instrument panel. (Scheme 62) Diagnostic codes can be obtained through TDCL connector or check connector. Check connector is located near top front of engine. (Scheme 63)
On all models, turn ignition on. DO NOT start engine. Using a jumper wire, connect terminals E1 and TE1 together either on TDCL connector or check connector. (Scheme 64) Count number of flashes from CHECK ENGINE light.
If CHECK ENGINE light flashes 2 times every second, system is normal. If a diagnostic code is displayed, first group of flashes will indicate first digit of a 2-digit diagnostic code. After a 1.5 second delay, second group of flashes will indicate second digit of diagnostic code.
If more than one code is stored, a 2.5 second delay will occur between diagnostic codes. After all diagnostic codes have been displayed, a 4.5 second delay will occur, and then diagnostic codes will be repeated until jumper wire connecting terminals E1 and TE1 is disconnected. Diagnostic codes will display from smallest to largest number.
Record diagnostic codes. Refer to «DIAGNOSTIC CODE IDENTIFICATION»(/lexus/ls/i-1989-1994/remont/testing-diagnostics/#engine-controls-tests-wcodes) table for identification. After reading diagnostic code description, see appropriate diagnostic code chart. To clear codes, see «CLEARING CODES»(/lexus/ls/i-1989-1994/remont/testing-diagnostics/#engine-controls-tests-wcodes__clearing-codes).

Test Mode

This mode detects same malfunctions as normal mode. It also detects malfunctions in starter signal circuit, No. 1 and No. 2 cam position sensors, idle contact signal of TPS, A/C signal and neutral start switch signal. Test mode is more sensitive to intermittent and regular faults. This mode is used for road test conditions.
To read diagnostic codes, ensure battery voltage is at least 11 volts, throttle valve is fully closed, transmission is in Neutral and all accessories are off. Total Diagnostic Communication Link (TDCL) connector is located under left side of instrument panel. (Scheme 62)
Turn ignition off. Using a jumper wire, connect terminals E1 and TE2 together on TDCL connector. (Scheme 64) Turn ignition on. DO NOT start engine. NOTE: If terminals E1 and TE2 are connected after ignition is turned on, test mode will not start.
When ignition is turned on, CHECK ENGINE light on instrument panel should flash. If CHECK ENGINE light does not flash, see TERMINAL TE1 & TE2 CIRCUIT DIAGNOSIS under CIRCUIT DIAGNOSIS CHARTS in I - SYS/COMP TESTS article in this section.
Start engine. Perform road test and simulate conditions described by customer. DO NOT disconnect jumper wire connecting terminals E1 and TE2. After road test, connect terminals E1 and TE1 together on TDCL connector using a jumper wire.
Count number of flashes from CHECK ENGINE light. System is normal if CHECK ENGINE light flashes 2 times every second. If a diagnostic code is displayed, first group of flashes will indicate first digit of a 2-digit diagnostic code. After a 1.5 second delay, second group of flashes will indicate second digit of diagnostic code.
If more than one code is stored, a 2.5 second delay will occur between diagnostic codes. After all diagnostic codes have been displayed, a 4.5 second delay will occur, and then diagnostic codes will be repeated until jumper wire connecting terminals E1 and TE1 is disconnected. Diagnostic codes will display from smallest to largest number.
After completing check, disconnect terminals TE1 and TE2 from terminal E1 on TDCL connector. Diagnostic Codes 17, 18 and 43 will set if engine is not cranked when entering test mode. This is normal. If automatic transmission is in D, 2, L or R, A/C switch is in ON position or accelerator pedal is depressed, Code 51 will set. This is normal.
Record diagnostic codes. See «DIAGNOSTIC CODE IDENTIFICATION»(/lexus/ls/i-1989-1994/remont/testing-diagnostics/#engine-controls-tests-wcodes) table for identification. After reading description of diagnostic code, see appropriate diagnostic code chart. To clear codes, see CLEARING CODES.

MOMENTARY INTERRUPTION TEST

During diagnosis, if Codes 13, 22, 24, 41 or 47 are stored in ECU memory and no trouble can be found with these circuits, perform the following MOMENTARY INTERRUPTION TEST.

Clear codes from ECU memory. See «CLEARING CODES»(/lexus/ls/i-1989-1994/remont/testing-diagnostics/#engine-controls-tests-wcodes__clearing-codes) . With ignition off, connect a jumper wire between terminals E1 and TE2 of TDCL connector.
Start engine. Ensure CHECK ENGINE light goes out. Pull lightly on wires and apply vibration to connectors and relays associated with diagnostic codes.
If CHECK ENGINE light illuminates during this test, a fault is in indicated connector or indicated location in wiring harness. Repair as necessary.
Clear diagnostic codes. Start engine. If CHECK ENGINE light does not go out, check thoroughly for faulty connections. Perform MOMENTARY INTERRUPTION TEST again. If CHECK ENGINE light still will not go out, see CONTROL UNIT in I - SYS/COMP TESTS article in this section.
Clear diagnostic codes. Start engine. If CHECK ENGINE light does not go out, check thoroughly for faulty connections. Perform MOMENTARY INTERRUPTION TEST again. If CHECK ENGINE light still will not go out, see CONTROL UNIT in I - SYS/COMP TESTS article in this section.

Note. Electronically Controlled Transaxle (ECT) uses same ECU as EFI system. For ECT transaxle diagnostics, see appropriate TRANSMISSION SERVICE & REPAIR article.

TROUBLE CODE DEFINITION

Note. Electronically Controlled Transmission (ECT) uses same ECU as EFI system.

Code	CHECK ENGINE Light	Signal Affected
12	(1) On	RPM Circuit No. 1
13	(2) On	RPM Circuit No. 2
14	(1) On	Ignition No. 1
15	(1) On	Ignition No. 2
16	(1) On	(3) ECT Control
21	(2) On	Main Oxygen Sensor (Left Bank)
22	(2) On	Water Temperature Sensor
24	(2) On	Intake Air Temperature Sensor
25	(2) On	Air/Fuel Ratio Lean Malfunction
26	(2) On	Air/Fuel Ratio Rich Malfunction
27	(2) On	Sub-Oxygen Sensor (Left Bank)
28	(2) On	Main Oxygen Sensor (Right Bank)
29	(2) On	Sub-Oxygen Sensor (Right Bank)
31	(1) On	Airflow Meter
35	(2) On	(5) HAC Sensor
41	(2) On	Throttle Position Sensor
43	(4) NA	Starter
47	(2) On	Sub-Throttle Position Sensor
51	(4) NA	Switch Condition
52	(1) On	No. 1 Knock Sensor
53	(1) On	Knock Control
55	(1) On	No. 2 Knock Sensor
71	(2) On	EGR System Malfunction
(1) If vehicle is in test mode, diagnosis would not be performed on this item. (2) If vehicle is in test mode, CHECK ENGINE light would be on. (3) Electronically Controlled Transmission (ECT). (4) If vehicle is in test mode, CHECK ENGINE light would be off. (5) High Altitude Compensator (HAC) sensor.

(1)	If vehicle is in test mode, diagnosis would not be performed on this item.

(2)	If vehicle is in test mode, CHECK ENGINE light would be on.

(3)	Electronically Controlled Transmission (ECT).

(4)	If vehicle is in test mode, CHECK ENGINE light would be off.

(5)	High Altitude Compensator (HAC) sensor.

DIAGNOSTIC CODE IDENTIFICATION

CLEARING CODES

Turn ignition off. Remove EFI fuse (20A) for at least 10 seconds. EFI fuse (20A) is located in junction block No. 2. This junction block is located in left front engine compartment.

Codes can be cleared by disconnecting negative battery cable.

Note. When disconnecting negative battery cable to clear codes, remember to reset clock and radio memory. After clearing codes, ensure a normal code is shown on CHECK engine light.

ECU LOCATION

For ECU location (Scheme 66)or (Scheme 67).

Scheme 65

Scheme 65: ECU LOCATION

SUMMARY

If no hard fault codes (or only pass codes) are present, driveability symptoms exist or intermittent codes exist, proceed to TESTS W/O CODES article in this section.for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.