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Harry Lemmens

Posts: 51
Reg: 11-2004

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Friday, November 19, 2004 - 12:46 am, by:  Harry Lemmens Edit Post Delete Post Print Post   View Post/Check IP (Moderator/Admin Only) Move Post (Moderator/Admin Only)

Toyota Soarer / SC400 EFI Diagnostics

V8 Engine

It has become obvious that many people do not really know how to do simple diagnostics on their vehicles. To that end this document has been prepared. It shows how to run the EFI diagnostics on a Soarer/Lexus SC400. Although specifically for V8 Soarers (Lexus SC400 for the US variant), the diagnostics are relatively general, and as such, apply to many different vehicles marketed by Toyota and Lexus.
There are other diagnostic procedures relevant to the brake and “Air conditioning” sections of the vehicle.

NB: The same fault codes are often shared by the 2.5 litre twin turbo, and the 3 litre normally aspirated SC300. If there is time, it may also include the fault codes from the Japanese manual, although translation of these will be left up to the end user, as I cannot read Japanese.

Where possible, I will also outline some diagnostic modes that are of interest. IE, “Track day” mode, which significantly alters the suspension “feel” on some vehicles. (Depends on their OEM suspension, not all cars have the relevant shock absorbers fitted, and some vehicles have been fitted with aftermarket suspension, thus loosing most (if not all) of this ability.)

Most of the following has been lifted from the “Soarer Bible”. (And mostly from the Lexus SC300/SC400 English manual.) Often, a reference will be noticed to another area. This reference describes further diagnosis and/or the repair procedure. It is NOT the intent of this document to go beyond the fault codes and their simple descriptions.

If you need more information, you could ask on the relevant club forum, you could get yourself a copy of the relevant CD’s containing the information you need, or you might purchase the appropriate workshop manuals from your local Toyota or Lexus dealership. (Genuine manuals are easier to use!) The CD can be purchased from several sources, notably Jeff Harper (, or from for our pommy mates in the United Kingdom.

Engine Part Locations

Location of Parts

The following describes the TWO different methods for getting into EFI and Automatic transmission diagnostics mode/s. Please note, EMV equipped vehicles have modes that can be activated via means other than those described below, however, I will not describe those techniques here. (Perhaps later? The techniques shown are more general in that they apply to all vehicle types, irrespective of fitted options! Also note that the dash displayed in the diagram is for the US version. It is still appropriate for the Japanese version digital display. (See note further down about the engine check symbol.)

Please Note: Vehicles later than about 1994 employed heated oxygen sensor modules in the exhaust system. Prior to that, the sensors were NOT heated. Ignore any reference to heated sensors if your vehicle is pre-1995.

Eng test (normal mode)

Figure 2 Normal Test Mode

The next page shows a “secondary” EFI test mode. This mode will display all the tests shown by the mode described above, as well as a few extra’s that the above test ignores. It also picks up a failure the first time it (a failure) is detected, unlike the “Normal” mode testing.

Test mode

Figure 3 EFI "Test" mode diagnostic procedure.

NB: I believe the ENGINE CHECK LAMP cat overheat symbol is the Catalytic Converter overheat symbol on Soarer digital dashes!

The following few pages describe the fault codes that the above test procedures may display.

EFI DTC’s 12 to 21

Figure 4 EFI Diagnostic Trouble Codes 12 to 21

EFI DTC’s 22 to 29

Figure 5 EFI Diagnostic Trouble Codes 22 to 29

EFI DTC’s 31 to 55

Figure 6 EFI Diagnostic Trouble Codes 31 to 55

EFI DTC’s Last Page

Figure 7 EFI Diagnostic Trouble Codes 71, 78 and 51.

The next list describe the “nastier” class of problems that may occur that provoke the “Limp Home” mode of operation of the ECU. Although the car may still be driveable, the engine operation will be severely curtailed.

EFI Failsafe Codes

Figure 8 EFI "Failsafe" Codes.

And, of course, it helps to be able to clear off trouble codes you think you may have fixed!

DTC Clearance

Figure 9 EFI Trouble Code Clearance.

Wiring 1

Wiring 2

Figure 10 Simplified Wiring Diagrams.

NB: this diagram is especially useful for people “transplanting” the 1UZFE and its ECU into donor vehicles. (IE: Cobra kit cars, etc) I strongly suggest wiring in the “malfunction” lamp (“W”) so diagnostics may still be performed!

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