Engine Controls - Tests W/codes — Toyota Corolla VI (1987-1993)

INTRODUCTION

Note. Federal model of Corolla (4A-F) are not equipped with a self-diagnostic system.

If no faults were found while performing BASIC TESTING , proceed with ENTERING TESTS W/CODES . If no trouble codes or only pass codes are present, proceed to TESTS W/O CODES for diagnosis by symptom (i.e. ROUGH IDLE, NO START, etc.).

ECU LOCATION

ECU is located at bottom center of dash, in front of console. On carbureted models, ECU is also known as Emission Control Computer (ECC).

"HARD FAILURES"

Hard failures cause "CHECK ENGINE" light to illuminate and remain on until the malfunction 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, vehicle is functional, but loss of good driveability will most likely be encountered.

"INTERMITTENT FAILURES"

Intermittent failures may cause "CHECK ENGINE" light to flicker or illuminate and go out after the intermittent fault goes away. The corresponding trouble code, however, will be retained in control unit memory. If related fault does not reoccur within a certain time frame, related trouble code will be erased from control unit memory. Intermittent failures may be caused by sensor, connector or wiring related problems. See INTERMITTENTS in TESTS W/O CODES section.

CHECK ENGINE LIGHT

Check engine light will come on when ignition switch is in "ON" position and engine is not running. When engine is started, "CHECK ENGINE" light should go off. If light remains on while engine is running, trouble code is present.
If light did not come on with key on and engine off, the "CHECK ENGINE" light circuit must be checked before continuing. Perform the "DIAGNOSTIC CIRCUIT CHECK" for the particular model. Circuit checks are located with the trouble code charts.

RETRIEVING TROUBLE CODES

CAUTION

DO NOT enter self-diagnostic system until all basic engine checks (engine, fuel and spark) have been performed. See the BASIC TESTING article in this section.

Scheme 42

Verify "CHECK ENGINE" light circuit is operational. Ensure battery voltage is above 11 volts and charging system is okay. Engine must be at normal operating temperature.
Transmission/transaxle must be in Neutral or Park. Air conditioner and other accessories must be off. Throttle valve must be closed (throttle position idle contacts closed).
Turn ignition switch to "ON" position with engine off. Place jumper wire across "TE1" (or "T") and "E1" terminals in engine check connector. (Scheme 42)
Count number of flashes from "CHECK ENGINE" light. If system is operating properly (with no codes), "CHECK ENGINE" light will blink continuously and evenly. (Scheme 43) NOTE: If "CHECK ENGINE" light stays on and will not blink codes, verify battery voltage is present at "TE1" (or "T") with key on and engine off. Ensure "E1" has continuity to ground or self-diagnostics will not work. If ground ("E1") is open, jumper "TE1" (or "T") to battery ground.
A trouble code will be identified by a.5 second flash on and off for the first number. A 1.5 second pause will occur followed by the second number. (Scheme 43)
If more than one code is stored, a 2.5 second pause will occur before second code is flashed. Once all codes have been displayed, a 4.5 second pause will occur and code(s) will repeat.
Trouble codes are given from smallest number code to largest number code. After codes are retrieved, remove jumper wire to exit diagnostic mode.

Scheme 43

NOTES ON TROUBLE CODES

No other code will appear with code 11.
When the malfunction in the system is repaired, the "CHECK ENGINE" light will go off but, the trouble code will remain in memory until the code is cleared.
If trouble code 51 is still displayed after clearing the ECU memory, check if A/C switch is "OFF" and throttle valve is fully closed. Place gearshift lever in "P" or "N". Clear trouble code again. If code will not clear, recheck switches and circuit.
If a malfunction occurs in test mode, the "CHECK ENGINE" light will remain on (all except code 51). ECU will erase all trouble codes when the ignition switch is turned off in test mode.

CLEARING TROUBLE CODES

After repairs are performed, clear ECU memory. To clear memory, turn ignition off. Remove fuse from main fuse block for about 30 seconds or more.
Fuse block is located below left side of instrument panel. See «CLEARING CODES»(/toyota/corolla/vi-1987-1993/remont/testing-diagnostics/#engine-controls-tests-wcodes) table for appropriate fuse.
Fuse may require to be removed longer depending on the ambient temperature. Replace fuse and exit diagnostic mode. Trouble codes can also be cleared by disconnecting vehicle battery. However, other memory functions (clock, radio, etc.), will need to be reset.

Application	Fuse (Amperage)
Corolla	STOP (15)

CLEARING CODES

REPAIR PROCEDURE

CAUTION

Ensure trouble codes are cleared after performing repair. Road test and recheck that trouble codes do not exist.

Locate and repair cause of trouble code. See appropriate TROUBLE CODE IDENTIFICATION table. Always repair faults in order from lowest numbered trouble code to highest numbered code.
Test drive vehicle after repairs are made to ensure no new codes are set.

NO CODES PRESENT, DRIVEABILITY COMPLAINT STILL PRESENT

If no codes are present but driveability complaint is still present, go to TESTS W/O CODES article in this section.
Also check fuel system pressure. See I - SYS/COMP TESTS article in this section.
Circuit voltages may also be checked at the computer. See J - PIN VOLTAGES CHARTS article.

Note. To check voltages at ECU pin connectors, see J - PIN VOLTAGES CHARTS article in this section. For more testing information, see I - SYS/COMP TESTS article in this section.

TROUBLE CODE CHARTS

Code No.	System Affected	Probable Cause
No Code	System Normal	System Normal
11 (1)	ECU (B+)	Ign. Switch/Circuit, ECU Main Relay/Ckt
12 & 13	RPM Signal	Dist./Circuit, ECU
14	Ignition Signal	Igniter/Circuit, Ign. Coil/Ckt, ECU
21	O2 Sensor & O2 Heater Signal	O2 Sensor/Ckt, (2) O2 Sensor Heater/Ckt, ECU
22	Temp. Sensor/Switch Signal	Coolant Temp. Sensor/Ckt, Coolant Temp. Switch/Ckt, ECU
24	Intake Air Temp. Sensor Signal	Intake Air Temp. Sensor/Ckt, ECU
25	Lean Air/Fuel Mixture	Injector/Ckt, O2 Sensor/Ckt, ECU, Fuel Line Press., Air Leak, Airflow Meter, Ignition System
26	Rich Air/Fuel Mixture	Injector/Ckt, O2 Sensor/Ckt, Fuel Line Press., Airflow Meter, (1) Vacuum Sensor, Cold Start Injector, ECU
27 (2)	Sub-O2 Sensor Signal	Sub-O2 Sensor/Circuit, ECU
31 (3)	Airflow Meter/Vac. Sensor Signal	Airflow Meter/Ckt, ECU, Vacuum Sensor/Circuit, Vacuum Switch/Circuit
42	Vehicle Speed Sensor Signal	Vehicle Speed Sensor/Ckt, ECU
43	Starter Signal	Ignition Switch/Ckt, ECU, Starter Signal Ckt
51	Switch Signal	A/C Switch/Ckt, A/C Amplifier, Throttle Position Sensor/Ckt, ECU
71 (4)	EGR System Malfunction	EGR System (valve, hoses, temp. sensors, vacuum switching valves), ECU
72	Fuel Cut Solenoid Signal	Fuel Cut Solenoid/Ckt, ECU
(1) Corolla 4A-FE only. (2) Corolla 4A-GE only. (3) Corolla 4A-GE use airflow meter. With 4A-FE use vacuum sensor. (4) Not used on Corolla 4A-FE. California only.

(1)	Corolla 4A-FE only.

(2)	Corolla 4A-GE only.

(3)	Corolla 4A-GE use airflow meter. With 4A-FE use vacuum sensor.

(4)	Not used on Corolla 4A-FE. California only.

TROUBLE CODE IDENTIFICATION

Trouble Code	Diagnostic Hints
11	Momentary Interruption Of Power Supply To ECU Could Also Indicate Loss Of ECU E1 Ground Connection
12	No "Ne" (RPM) Ignition Signal To ECU Within 2 Seconds After Engine Is Cranked No "G" Ignition Signal To ECU 2 Times In A Row When Engine Speed Is Between 500-4000 RPM
13	No "Ne" (RPM) Ignition Signal To ECU When Engine Speed Is Above 1500 RPM Signal Is Generated By Pick-Up Coils In Distributor
14	No "IGF" Ignition Signal To ECU From Ignitor Several Times In Succession
21	(1) Detects Deterioration Of Oxygen Sensor Open Or Short In Oxygen Sensor Circuit
22	Open Or Short In Coolant Temp. Sensor/Switch Signal
24	Open Or Short Circuit In Intake Air Temp. Sensor Signal
25	Open Circuit In O2 Sensor Signal Signal Sent By O2 Sensor For Several Seconds During Air/Fuel Ratio Feedback Correction
26	Rich Signal Sent By O2 Sensor For Several Seconds During Air/Fuel Ratio Feedback Correction
27	Open Or Short In Sub-O2 Sensor Signal
31 (4A-FE Only)	Open Or Short In Vacuum Sensor/Switch Signal
31 & 32	Short Circuit Between Terminals Of Airflow Meter
34	Turbocharger Pressure Is Abnormal Code May Also Set If Airflow Meter Is Faulty
35	Open Circuit In High Altitude Compensator Signal
41	Open Or Short In Throttle Position Sensor Signal "IDL" & "PSW" Signals Are Output At Same Time For Several Seconds
42	No "SPD" Signal From Vehicle Speed Sensor For 8 Seconds With Engine Speed Between 2300-5500 RPM & Coolant Temp. Is Below 176°F (80°C) Except When Racing The Engine
43	No "STA" Signal To ECU Until Engine Reaches 800 RPM With Vehicle Not Moving
51	Problem In One Of 3 Switches ECU Monitors, Throttle Position Sensor ("IDL" Signal) Neutral Safety Switch ("NSW" Signal On A/T) A/C Signal To ECU Occurs When TPS Is At Idle & A/C Switch Is "ON" And Check Connector "E1" And "TE1" Is Jumpered
52	Open Or Short Circuit In Knock Sensor Signal
53	Knock Control In ECU Is Faulty
71	EGR Valve Normally Closed, Or Clogged Hose Open Circuit In EGR Temperature Sensor Signal EGR Gas Below Predetermined Level During EGR Control
72	Open Circuit In Fuel-Cut Solenoid Signal
(1) Also detects faults in O2 sensor heater, if equipped.

(1)	Also detects faults in O2 sensor heater, if equipped.

TROUBLE CODE DIAGNOSTIC HINTS (FUEL INJECTED VEHICLES)

Scheme 44

Scheme 44: 4A-FE & 4A-GE DIAGNOSTIC CIRCUIT CHECK

Scheme 45

Scheme 45: 4A-FE & 4A-GE ECU TERMINAL IDENTIFICATION

Scheme 46

Scheme 47

Scheme 47: TEST 1 OR CODE 11 - ECU (+B) CIRCUIT (4A-FE & 4A-GE)

Scheme 48

Scheme 49

Scheme 50

Scheme 50: TEST 2 - ECU POWER SOURCE (4A-FE & 4A-GE)

Scheme 51

Scheme 51: TEST 3 OR CODE 12, 13, 14 - IGNITION & RPM SIGNAL

Scheme 52

Note. To check ignition system components, see IGNITION SYSTEMS in I - SYS/COMP TESTS article

Note. Code 12 is caused by the loss of "NE" or "G" signal to distributor or ECU during cranking. Code 13 is caused by loss of the "NE" signal to distributor or ECU when engine RPM exceeds 1000 RPM.