Toyota Tercel 1984-1994 Repair Guide

Self Diagnostics


The electronic control modules (ECM) on some 3E engines and all 3E-E engines contain a built-in self diagnosis system. When troubles with the engine control network are detected, the "Check Engine'' lamp on the dash panel will light. At the same time the trouble is identified by circuit and a diagnostic code is recorded within the ECM. This diagnostic code can be read by the number of flashes the Check Engine lamp displays when both check engine terminals are shorted together under the hood.

In the event of an internal computer malfunction, the ECM is programmed with back-up or default values. This allows the car to run on a fixed set of values for engine operation. Driveability may suffer since the driving conditions cannot be dealt with by the faulty computer. This back-up programming allows the computer to fail with out stranding the car, hence the nickname "fail-safe''. No computer is safe from failure, but a back-up system helps make the best of the situation.

Many problems in this system are the result of poor connections, vacuum leaks, charging system problems and other relatively minor conditions. Trouble code listings are included in this section as a guide to solving some of these simpler problems. However, if a problem cannot be found quickly and further diagnosis is necessary, it should be left to a qualified technician as they involve complex procedures and expensive equipment.


See Figures 1, 2 and 3

  1. The following initial conditions must be met or the code will not be transmitted from the ECM:
    1. Battery voltage above 11 volts
    3. Throttle plate fully closed - keep your foot off the accelerator
    5. Transmission selector in neutral
    7. All accessory switches off

  3. Turn the ignition switch ON, but DO NOT start the engine.
  5. Use a service (jumper) wire to short together terminals T and E1 of the engine check connector.

The diagnostic code(s) will be indicated by the number of flashes of the Check Engine light. If the system is normal, the light will blink repeatedly about every 1 / 2 second. If a fault code is stored, its two digit code will be indicated in the pattern of the flashing. For example, code 21 would be indicated by two flashes, a pause, and one flash. There will be about a 1 1 / 2 second pause between the first and second digit of a code. If more than one code is stored, the next will be transmitted after a 2 1 / 2 second pause. Once all the codes have been flashed, the system will wait 4 1 / 2 seconds and repeat the entire series. It will continue sending the fault codes as long as the initial conditions are met and the engine check connector is shorted across terminal T and E1 .

If more than one code is stored, they will be delivered in numerical order from the lowest to the highest, regardless of which code occurred first. The order of the codes DOES NOT indicate the order of occurrence.

  1. After the code(s) have been read and recorded, turn the ignition switch to OFF and disconnect the jumper wire.

Disconnecting the wire with the ignition ON may cause severe damage to the ECM.

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Fig. Fig. 1: Trouble codes for 3E engines

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Fig. Fig. 2: Trouble codes for 3E-E engines

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Fig. Fig. 3: Trouble codes for 3E-E engines


Once the codes have been read and recorded, the memory on the ECM may be cleared of any stored codes by removing the power to the ECM for at least 1 minute. On 3E engines, remove the 15 amp RADIO No.1 fuse. On 3E-E engines, remove the 15 amp EFI fuse.

The ignition MUST be OFF when the fuse is removed and reinstalled. Serious damage to the ECM may occur if this precaution is not followed.

Remember that the codes are there to indicate a problem area. Don't clear the code just to get the dashboard light off - find the problem and fix it for keeps. If you erase the code and ignore the problem, the code will reset (when the engine is restarted) if the problem is still present.

The necessary time to clear the computer increases as the temperature drops. To be safe, remove the fuse for a full minute under all conditions. The system can also be cleared by disconnecting the negative battery cable, but this will require resetting other memory devices such as the clock and/or radio. If for any reason the memory does not clear, any stored codes will be retained. Any time the ECM is cleared, the car should be driven and then re-checked to confirm a normal signal from the ECM.