Toyota Service Blog

Procedures to Retrieve Trouble Codes

There are several different types and locations of diagnostic connectors which are used to trigger and, in some cases, read diagnostic code output from Toyota EFI engines. All late model TCCS applications, from 1988, use a multiple terminal diagnostic check connector. Earlier models use this same multiple terminal or a two-terminal check connector, all located under the hood.

The procedure to examine the ECU memory for diagnostic codes is typically very simple regardless of which vintage engine being diagnosed. All engines equipped with self diagnostic systems have one terminal of the check connector identified as T or TE1. When grounded, this terminal triggers the self diagnostic feature of the ECU. The E1 ground circuit is also located in the check connector.

To enter engine diagnostics:

• Locate the check connector under the hood and identify the T (TE1 on late model TCCS) and E1 terminals.

• Turn the ignition switch to the "on" position and make sure that the check engine light is on.

• Confirm that the throttle is closed (IDL contact on).

• Jumper check connector terminals T (TE1) to E1.

When the T terminal is grounded with the ignition switch in the "on" position, the ECU sees the voltage at terminal T go low. Low voltage on T causes the ECU to enter diagnostic mode, producing diagnostic codes on the check engine light. On '83 through '85 Cressida and Supra models, the check engine light does not flash diagnostic codes. An analog voltmeter must be used to read the codes from the VF terminal of the EFI Service Connector.

Depending on the vintage of the system being tested, the codes will be displayed in either one or two digit format. It is important to refer to the proper repair manual for specific information about diagnostic connector location, code format, and proper procedures for the vehicle you are troubleshooting.

'83 THROUGH '85 CRESSIDA AND SUPRA

'83 THROUGH '85 CRESSIDA AND SUPRA

Super Monitor Display: On some 1983 through 1987 Cressida and Supra models, a Super Monitor trip computer was offered as optional equipment. This display can be used to read diagnostic codes by simply pressing and holding the monitor "Select" and "Input M" keys together, for three seconds, with the ignition switch in the "on" position. When the "DIAG" message appears on the display, pressing and holding the "Set" key for three seconds will put the TCCS system into diagnostic mode. The display will indicate any diagnostic codes stored in the ECU's keep alive memory.

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