Engine Controls - Tests W/o Codes Toyota Tercel L40

INTRODUCTION

Before diagnosing symptoms or intermittent faults, perform steps in BASIC DIAGNOSTIC PROCEDURES and G-TESTS W/CODES articles in this Section. Use this article to diagnose driveability problems existing when a hard fault code is not present or vehicle is not equipped with a self-diagnostic system.

Note. Some driveability problems may have been corrected by manufacturer with a revised computer calibration chip or computer control unit. Check with manufacturer for latest chip or computer application.

Symptom checks can direct the technician to malfunctioning component(s) for further diagnosis. A symptom should lead to a specific component test, system test or adjustment.

Use intermittent test procedures to locate driveability problems that DO NOT occur when the vehicle is being tested. These test procedures should also be used if a soft (intermittent) trouble code was present, but no problem was found during self-diagnostic testing.

Note. For specific testing procedures, see I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section. For specifications, see ADJUSTMENTS or SPECIFICATIONS article in the ENGINE PERFORMANCE Section.

SYMPTOM DIAGNOSIS

Symptom checks cannot be used properly unless the problem occurs while the vehicle is being tested. To reduce diagnostic time, ensure steps in BASIC TESTING and TESTS W/CODES articles in the ENGINE PERFORMANCE Section were performed before diagnosing a symptom. The following symptoms are available for diagnosis.

1. Difficult To Start/No Start (Engine Will Not Crank Or Cranks Slowly)
2. Difficult To Start/No Start (Cranks Okay)
3. Engine Stalls Often
4. Engine Stalls Occasionally
5. Rough Idle/Missing
6. High Idle Speed (No Drop)
7. Engine Backfires (Lean Fuel Mixture)
8. Muffler Explosion (Rich Fuel Mixture)
9. Engine Hesitates/Poor Acceleration

DIFFICULT TO START/NO START (ENGINE WILL NOT CRANK OR CRANKS SLOWLY)

1. Check grounds.
2. Check battery and cables, charging system and fusible links.
3. Check ignition switch.
4. Check starter relay.
5. Check clutch start switch (M/T) or neutral start switch (A/T).
6. Check starter and wiring connections.
7. Check timing belt.

DIFFICULT TO START/NO START (CRANKS OKAY)

1. Check for vacuum leaks (oil filler cap, oil dipstick, hose connections, PCV hose and valve, etc.).
2. Verify secondary ignition system performance.
3. Ensure ignition timing is correct.
4. Check cam position sensor (if equipped).
5. Ensure fuel system performs properly (pump, lines, filter, pressure regulator and cold start injector).
6. Check circuit opening relay.
7. Check fuel pump switch in airflow meter (if equipped).
8. If engine starts with accelerator pedal depressed, check idle speed control valve (if equipped) and wiring connection.
9. Check auxiliary air valve (if equipped).
10. Check wiring connection to ECU.
11. Check power to ECU via fusible links, fuses and EFI main relay.
12. Check airflow meter, coolant temperature sensor and air temperature sensor.
13. Check engine compression and valve clearance.
14. Check injection signal circuit.
15. Check timing belt.

ENGINE STALLS OFTEN

1. Check for vacuum leaks (oil filler cap, oil dipstick, hose connections, PCV hose, PCV valve and EGR system).
2. Ensure fuel system functions properly (pump, lines, filter, and pressure regulator).
3. Check air filter.
4. Check idle speed, and ensure ignition timing is correct.
5. Verify secondary ignition system performance.
6. Check cold start injector and cold start injector time switch.
7. Check auxiliary air valve or idle speed control valve (if equipped).
8. Check circuit opening relay.
9. Check fuel injectors (low fuel pressure or leaking injectors).
10. Check power to ECU via fusible links, fuses and EFI main relay.
11. Check airflow meter, TPS, coolant temperature sensor and air temperature sensor.
12. Check injection signal circuit.
13. Check engine compression and valve clearance.
14. Check Electronic Control Unit (ECU).

ENGINE STALLS OCCASIONALLY

1. Check airflow meter and connectors.
2. Check EFI main relay, circuit opening relay and connectors. Check for slight change in engine idle when connector or relay are slightly tapped or wiggled.
3. Check A/C switch, dashpot and throttle opener.
4. Check for sticking EGR valve.

ROUGH IDLE/MISSING

1. Check for vacuum leaks (oil filler cap, oil dipstick, hose connections, PCV hose, PCV valve and EGR system).
2. Check idle speed control valve.
3. Check air filter.
4. Check idle speed and ensure ignition timing is correct.
5. Verify secondary ignition system performance.
6. Check airflow meter, coolant temperature sensor and air temperature sensor.
7. Check engine compression and valve clearance.
8. Check variable induction system (if equipped).
9. Check cold start injector and cold start injector time switch.
10. Ensure fuel system functions properly (pump, lines, filter and pressure regulator).
11. Check fuel injectors (low fuel pressure, clogged or leaking injectors).
12. Check power to ECU via fusible links, fuses and EFI main relay.
13. Check injection signal circuit.
14. Check O2 sensor(s).
15. Check Electronic Control Unit (ECU).

HIGH IDLE SPEED (NO DROP)

1. Check accelerator linkage, dashpot or throttle opener (if equipped).
2. Check power steering idle-up circuit (if equipped).
3. Check A/C idle-up circuit (if equipped).
4. Check idle speed control valve (if equipped) or auxiliary air valve (if equipped) and wiring.
5. Check variable induction system (if equipped).
6. Ensure ignition timing is correct.
7. Check throttle position sensor.
8. Check for high fuel pressure.
9. Check for leakage at cold start injector or fuel injectors.
10. Check power to ECU via fusible links, fuses and EFI main relay.
11. Check airflow meter, coolant temperature sensor and air temperature sensor.
12. Check injection signal circuit.

ENGINE BACKFIRES (LEAN FUEL MIXTURE)

1. Check for vacuum leaks (oil filler cap, oil dipstick, hose connections, PCV hose, PCV valve and EGR system).
2. Check idle speed and ensure ignition timing is correct.
3. Check airflow meter, coolant temperature sensor, throttle position sensor and air temperature sensor.
4. Check cold start injector and cold start injector time switch.
5. Ensure fuel system functions properly (pump, lines, filter and pressure regulator).
6. Check for clogged fuel injectors.
7. Check power to ECU via fusible links, fuses and EFI main relay.
8. Check injection signal circuit.
9. Check O2 sensor(s).

MUFFLER EXPLOSION (RICH FUEL MIXTURE)

1. Check idle speed and ensure ignition timing is correct.
2. Check airflow meter, coolant temperature sensor, throttle position sensor and air temperature sensor.
3. Check cold start injector and cold start injector time switch.
4. Ensure fuel system functions properly (pump, lines, filter and pressure regulator).
5. Check for fuel injector leakage.
6. Verify secondary ignition system performance.
7. Check engine compression and valve clearance.
8. Check throttle position sensor and injection signal circuit.
9. Check O2 sensor(s).
10. Check for exhaust system leaks.

ENGINE HESITATES/POOR ACCELERATION

1. Check for clutch slipping or brakes dragging.
2. Check O2 sensor(s).
3. Check for vacuum leaks (oil filler cap, oil dipstick, hose connections, PCV hose, PCV valve and EGR system).
4. Check air filter.
5. Check airflow meter, coolant temperature sensor, air temperature sensor and throttle position sensor.
6. Check for leakage or clogging between air filter and turbocharger inlet, and between turbocharger outlet and cylinder head (if equipped).
7. Check secondary ignition system performance and ignition timing.
8. Verify timing belt alignment
9. Check engine compression and valve clearance.
10. Ensure fuel system functions properly (pump, lines, filter and pressure regulator).
11. Check for clogged fuel injectors.
12. Check variable induction system (if equipped).
13. Check power to ECU via fusible links, fuses and EFI main relay.
14. Check injection signal circuit.

INTERMITTENT PROBLEM DIAGNOSIS

Intermittent fault testing requires duplicating circuit or component failure to identify the problem. These procedures may lead to the computer setting a fault code, which may help in diagnosis.

If problem vehicle does not produce fault codes, use DVOM to help pinpoint faults. Monitor voltage or resistance values while attempting to reproduce conditions causing intermittent fault. A status change on DVOM indicates area of fault.

When monitoring voltage, ensure ignition switch is in ON position or engine is running. Ensure ignition switch is in OFF position or negative battery cable is disconnected when monitoring circuit resistance.

Intermittent Simulation

To reproduce the conditions creating an intermittent fault, use the following methods

1. Lightly vibrate component. See VIBRATION METHOD.
2. Heat component. See HEAT METHOD.
3. Wiggle or bend wiring harness. See VIBRATION METHOD.
4. Spray suspect component with light water mist, or spray radiator with water to raise humidity. See HUMIDITY METHOD.
5. Remove/apply vacuum source.

Monitor circuit/component voltage or resistance while simulating intermittent. If engine is running, monitor for self-diagnostic codes. Use test results to identify a faulty component or circuit.

Wiring Harness Testing

Using DVOM, monitor suspect circuit or component. Lightly shake wiring harness while checking DVOM for voltage fluctuation. (Scheme 75) Inspect component connector harness for stretched areas. Inspect fulcrum point of harness at the body through-portion.

Component, Relay & Sensor Testing

Using DVOM, monitor suspect circuit or component. Lightly vibrate suspect component, relay or sensor, and check DVOM for voltage fluctuation. (Scheme 75)

Electrical Connector Testing

Using DVOM, monitor suspect circuit or component. Lightly shake connector while checking DVOM for voltage fluctuation. (Scheme 75) Visually inspect connector and repair if necessary.

HEAT METHOD

Using hair dryer or similar device, apply heat to suspect component. Monitor suspect circuit or component using a DVOM.

HUMIDITY METHOD

If humidity or moisture is suspected of causing intermittent failure, lightly spray water to the front of warm/hot radiator to increase humidity in the engine compartment. Check for malfunction by monitoring suspect circuit or component with a DVOM.

If vehicle has interior water leakage, the admitted water may contaminate ECU. When testing a vehicle that has interior water leakage, carefully inspect ECU terminals for corrosion. Repair or replace ECU and connectors if necessary. Repair interior water leakage problem.

ELECTRICAL LOAD METHOD

To check if intermittent fault occurs under electrical load, turn on all electrical loads (heater blower, headlights, rear window defogger, wipers, etc.). Check for malfunction by monitoring suspect circuit or component with a DVOM.

Scheme 75