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Info:- ECU Diagnostic Codes

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How to read the diagnostic codes from your MR2 Mk1 ECU

EFI SYSTEM — Diagnosis System


The ECU contains a built-in self-diagnosis system by which troubles with the engine signal network are detected and a "CHECK ENGINE" warning light on the instrument panel flashes.

By analysing various signals as shown in the later table the Electronic Control Unit (ECU) detects system malfunctions, which are related to the various operating parameter sensors or to actuator. The ECU stores the failure code associated with the detected failure until the diagnosis system is cleared by removing the AM2 fuse with the ignition switch off.

The "CHECK ENGINE" warning light on the instrument panel informs the driver that a malfunction has been detected.

The light goes out automatically when the malfunction has been cleared.


1. The "CHECK ENGINE" warning light will come on when the ignition switch is placed at ON and the engine is not running.

2. When the engine is started, the "CHECK ENGINE" warning light should go out.

If the light remains on, the diagnosis system has detected a malfunction or abnormality in the system.


To obtain an output of diagnostic codes, proceed as follows:

1. Initial conditions

(a) Battery voltage above 11 volts

(b) Throttle valve fully closed (throttle position sensor IDL points closed)

(c) Transmission in neutral position

(d) Accessory switches OFF

2. Turn the ignition switch to ON. Do not start the engine.

3. Using a service wire short terminals T and E1 of the check connector.

NOTE: The check connector is located near the resonator (4A-GE) or intercooler (4A-GZE).

4. Read the diagnostic code as indicated by the number of flashes of the CHECK ENGINE warning light.

Diagnostic Codes (TCCS ECU without Air Flow Meter)

(a) Normal System Operation (code 1)

The light will flash every 4.5 seconds

(b) Malfunction Code Indication

The light will flash a number of times equal to the malfunction code indication with a 2.5 second interval between each indication

After all the codes have been output, there will be a 4.5 second pause and they will be repeated as long as terminals T and E1 of the check connector are shorted.

NOTE. In the event of a number of trouble codes, indication will begin from the smaller value and continue in order to the larger.

5. After the diagnosis check, remove the service wire from the check connector

Cancelling Diagnostic Code

1. After repair of the trouble area, the diagnostic code retained in the memory of the ECU must be cleared by removing the AM2 (7.5A) fuse located in the engine compartment relay box for 10 seconds or more depending on the ambient temperature (the lower the temperature, the longer the fuse must be left out) with the ignition switch OFF

2. After cancellation, road test the car to check that the Normal code is now displayed. If the same code appears, the problem has not been properly repaired.


Note. When I was researching this I found that, depending on where you look there are different codes listed for the MK1. The copies of the Haynes manual and the BGB I have contain different codes. These codes were taken from the Toyota 4A-GE Engine Repair Manual. I have checked several of the codes with my 1988 UK spec T-bar and a 1986 UK spec coupe and they appear to be correct for a MAP engine car. The MAF engine cars appear to have different codes. If you know if any of these are wrong please contact me so I can correct any errors.

My thanks to Scottsmale for letting me check the codes on his car.

Jimi Lawson 20/08/05

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