Diagnosing Common Problems

The GT-Four is blessed with the legendary Toyota reliability but it is not invincible. Inevitably, with any high power 4WD car, the driver will be faced with a problem sooner or later.

In these pages we hope to help solve some of the more common ones

Understanding ECU Error Codes

Check Engine Light

If your dashboard warning light comes on, then you have a problem with your engine.

Most (but not all) problems are automatically detected and flagged by the car's ECU by lighting the Check Engine Light (CEL). It is worth noting that not all problems will turn on the CEL so it is worth performing regular checks to check for "invisible" codes


How To Check Error Codes

To find out what error the ECU has detected you need to switch it into diagnostic mode. To do this:-

Switch off the ignition. Locate the diagnostic box, under the bonnet behind the passenger suspension turret. The lid of the box hinges open and on the back of the lid there is a pinout of the connector. Locate the E1 and TE1 terminals and using a paperclip, piece of wire etc connect these two terminals together. Go back into the car and switch the ignition to on (but do not start the car) and observe the check engine light. It will do one of two things:-

A steady flashing indicates that there are no stored codes (as shown in the image above)

Otherwise, count the number of flashes and write down the number. There is a pause between each number, so if you count 5, then observe a pause, then count 4, that makes error code 54.

There may be multiple errors stored. It is a good idea to clear any codes once in a while, by disconnecting the negative terminal of the battery for a few seconds, or removing the EFI fuse in the fusebox for a few seconds and replacing it. This makes it easier to diagnose new problems.

Checking for error codes should always be your first port of call when trying to track down any engine running issues. Also, remember to make sure the Check Engine light is actually working It should illuminate when you turn the ignition to the running position but don't actually start the car

11ECU (+B)Momentary interruption in power to ECU
12RPM SignalNo NE or G signal to ECU within 2 seconds after engine has been cranked
13Ignition SignalNo NE signal to ECU when engine speed is above 1,000 rpm
14Ignition SignalNo IGF signal to ECU 8-11 times in succession
21Oxygen Sensor/Heater circuitDetection of oxygen sensor deterioration or open or short in oxygen sensor heater
22Water Temp SignalOpen or short in water temp. sensor signal (THW)
24Intake Air Temp. SensorOpen or short in intake air temp. sensor signal (THA)
25Air-fuel Ratio Lean MalfunctionOxygen sensor outputs a lean signal continuously for several seconds during air-fuel ratio correction. Open or short in oxygen sensor (OX)
26Air-fuel Ratio Rich MalfunctionOxygen sensor outputs a rich signal continuously for several seconds during air-fuel ratio correction
31Air-Flow Meter SignalOpen cct in VC signal or short cct between VS and E2 when idle contacts are closed
32Air-Flow Meter SignalOpen cct in E2 or short cct between VC and VS
34Turbocharging Pressure SignalFuel cut-off due to high turbocharging pressure
35Turbocharging Pressure Sensor SignalOpen or short in turbocharging sensor pressure signal (PIM)
41Throttle Position Sensor SignalOpen or short in throttle position sensor signal (VTA)
42Vehicle Speed Sensor SignalNo SPD signal for 8 seconds when engine speed is between 2,500rpm and 6,000rpm and coolant temperature is below 80C (176F) except when racing the engine
43Starter SignalNo STA signal to ECU until engine speed reaches 800rpm with vehicle not moving
51Switch SignalNo IDL signal or A/C signal to ECU, with check terminals TE1 and E1 shorted
52Knock Sensor SignalOpen or short in knock sensor signal (KNK)
53Knock Sensor Control Signal in ECUKnock control in ECU faulty
54 Intercooler (water/air)Intercooler pump problem

Error Code 54:- Water/Air Intercooler

This is a very common problem reported by owners of water/air intercooler cars (ST165, ST185RC).

Often this is very simple, just a matter of checking the coolant level in the intercooler reservoir. After topping up, you need to reset the ECU to clear the error code. You can do this by removing the EFI fuse from the fuse box for a few seconds, or disconnecting the negative terminal on the battery. This is necessary as the ECU will limit boost levels if code 54 is detected.

Error Code 54 may indicate a problem with the intercooler water circulation pump. If all else fails, you may need to replace the bearings in the pump as described here.

Some owners prefer their intercooler running constantly, rather than the haphazard on/off that the stock ECU seems to dictate. This will cause a problem with the ECU detecting code 54. There is a write up on pump overhaul in the maintenance section.