Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
1990 Toyota Corolla Base, AutomaticFACTORY OEM SERVICE PROCEDURE
Engine Controls - Tests W/Codes
- Introduction
- Ecu Location
- "Hard Failures"
- "Intermittent Failures"
- Check Engine Light
- Retrieving Trouble Codes
- Notes On Trouble Codes
- Clearing Trouble Codes
- Repair Procedure
- Summary
- Trouble Code Charts
- 4A-FE & 4A-GE Diagnostic Circuit Check
- 4A-FE & 4A-GE Ecu Terminal Identification
- Test 1 Or Code 11 - Ecu (+B) Circuit (4A-FE & 4A-GE)
- Test 2 - Ecu Power Source (4A-FE & 4A-GE)
- Test 3 Or Code 12, 13, 14 - Ignition & Rpm Signal
- Test 4 Or Code 21, 25, 26- Oxygen Sensor Signal (4A-FE & GE)
- Test 5 Or Code 22 - Coolant Temp Sensor Signal (4A-FE & GE)
- Test 6 Or Code 24 - Intake Air Temp Sensor (4A-FE & 4A-GE)
- Test 7 Or Code 31 - Airflow Meter/Vacuum Sensor
- Test 8 Or Code 41 - TPS Signal (4A-FE & 4A-GE)
- Code 42 - Vehicle Speed Sensor (VSS) Signal
- Test 9 Or Code 43 - Starter Signal (4A-FE & 4A-GE)
- Test 10 Or Code 51 - A/C Switch Signal (4A-FE & 4A-GE)
- Test 11 Or Code 71 - EGR System Malfunction (4A-FE & 4A-GE)
- Test 12 - Injector Circuit (4A-FE & 4A-GE)
- Test 13 - "Check Engine" Circuit (4A-FE & 4A-GE)
Factory Service Tools
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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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