Toyota Pick-ups/Land Cruiser/4Runner 1970-1988

Diagnosis and Testing



Do not operate the fuel pump when the fuel lines are empty.
Do not reuse fuel hose clamps.
Make sure all EFI harness connectors are fastened securely. A poor connection can cause an extremely high surge voltage and result in damage to integrated circuits.
Keep the EFI harness at least 4 in. away from adjacent harnesses to prevent system malfunction due to external electronic noise.
Keep all EFI parts and harnesses dry during service.
Before attempting to remove any parts, turn OFF the ignition switch and disconnect the battery ground cable.
Always use a 12 volt battery as a power source.
Do not attempt to disconnect the battery cables with the engine running.
Do not rev up the engine immediately after starting or just prior to shutdown.
Do not attempt to disassemble the EFI control unit under any circumstances.
If installing a 2-way or CB radio, mobile phone or other radio equipment, keep the antenna as far as possible away from the electronic control unit. Keep the antenna feeder line at least 8 in. away from the EFI harness and do not run them parallel for a long distance. Be sure to ground the radio to the vehicle body.
Handle the air flow meter carefully to avoid damage.
Do not disassemble the air flow meter or clean the meter with any type of detergent.
Before connecting or disconnecting control unit ECU harness connectors, make sure the ignition switch is OFF or the negative battery cable is disconnected.
When performing ECU input/output signal diagnosis, remove the water-proofing rubber plug, if equipped, from the connectors to make it easier to insert tester probes into the connector. Always reinstall it after testing.
When connecting or disconnecting pin connectors from the ECU, take care not to bend or break any pin terminals. Check that there are no bends or breaks on ECU pin terminals before attempting any connections.
Before replacing any ECU, perform the ECU input/output signal diagnosis to make sure the ECU is functioning properly.
When measuring supply voltage of ECU-controlled components with a circuit tester, keep the tester probes separated from each other and from accidental grounding. If the tester probes accidentally make contact with each other during measurement, a short circuit will result and damage the ECU.


Diagnosis codes are held in memory and may be displayed by grounding the proper terminals at the diagnostic connector or check connector. The system should be interrogated for stored codes before any disconnection of the battery cables; once disconnected, the stored codes will be lost. Certain conditions must be met before the codes will be transmitted from the ECU. The initial conditions are:

Engine at normal operating temperature
Battery voltage 11 volts or above
Throttle fully closed (IDL points engaged)
Transmission in N
All accessories and electrical loads OFF

If any of the initial conditions are not met, the ECU will note a problem and display a switch condition code when the diagnostic circuit is grounded.

Diagnostic Connector Locations

See Figure 1

On all equipped vehicles the check connector (near the ignition coil) or diagnostic connector are located under the hood in the engine area on the shock tower (passenger side) or near the junction or relay block (driver's side). A small plastic cap covers the check connector terminals and hinged plastic cap covers the diagnostic connector. Each terminal is mark inside the diagnostic cap cover for proper identification.

Click image to see an enlarged view

Fig. Fig. 1: Check connector (lower view) and diagnostic connector (upper view)

Reading Stored Codes
  1. Check that the initial conditions are met.
  3. Turn the ignition switch ON but do not start the engine.
  5. At the diagnostic connector or check connector, use a jumper wire to connect terminals T and E 1 .
  7. Observe the CHECK ENGINE warning lamp on the dashboard; read the code(s) based on the number and rate of flashes.
  9. If the system is operating normally, with no codes stored, the warning lamp will flash on/off in a constant, unchanging pattern. This is the System Normal signal; the ECU is acknowledging the request for codes but has nothing to report.
  11. If malfunction codes are stored, the light will blink every 1 / 2 -second. The first number of blinks will indicate the first digit of a 2-digit code. After a 1 1 / 2 second pause, the second digit will be transmitted. If there is more than one code stored, they will be separated by a 2 1 / 2 -second pause. After all stored codes have been transmitted, the cycle will begin again after a 4 1 / 2 second pause. The codes will continuously transmit until the jumper wire is disconnected. Even when transmission has stopped, the codes remain in memory until the memory is cleared.

If more than one code is stored, the codes will be transmitted in numerical order from lowest to highest. The order of the codes does not indicate the order of fault occurrence.

  1. Record the codes as they are received.
  3. Disconnect the diagnostic jumper; switch the ignition OFF .

Clearing Stored Codes

Stored codes will remain in memory until cleared. The correct method of clearing codes is to turn the ignition switch OFF , then remove the EFI 15A fuse for at least 30 seconds. The time required will be longer in cold weather.

Disconnecting the negative battery cable will also clear the memory but is not recommended due to other on-board memories being cleared as well. Once the system power is restored, re-check for stored codes. Only the System Normal indication should be present. If any other code is stored, the clearing procedure must be repeated or the old code will be stored with any new ones.

After repairs, it is recommended to clear the memory before test driving the vehicle. Upon returning from the drive, interrogate the memory; if the original code is again present, the repair was unsuccessful.