# 4WS Overview

(Please note for any location info this is based on a 91 JDM convertible- some locations for coupes will be slightly different)

## Introduction

The 4WS system was only available on JDM Celicas (other manufacturers had similar systems but not the same, e.g., Honda etc.). Therefore, there is no English workshop manual. If you can read Japanese, then make yourself known!

While the Japanese manual is readily available, the only sense to be made is using the pictures which, actually, do give quite a good indication of some diagnostic checks and wiring diagrams.

## Purpose of 4WS

The idea of 4WS is to:
- At slow speeds below 30kph (ish), the rear wheels turn opposite to the front wheels, giving a tight turning circle to aid maneuverability.
- At speeds over around 30kph, the wheels turn in unison. On a motorway, the car will 'crab' across lanes rather than turn.
- When going fast, it is supposed to negate oversteer and give a lot of grip through the corners.

## Dashboard Controls

There are 2 buttons on the dash for the 4WS system:
1. Rev2WS: Forces the back wheels to centralize but ONLY in reverse.
2. Sport/Norm switch: Not too sure what this does, but it's said to make you go round corners like on rails, even more so than in normal mode.

## Main Components

There are 7 main parts of the 4WS system:
1. The main 4WS ECU – mounted NSR wing in boot
2. The steering driver 4WS ECU – mounted next to the main 4WS ECU in boot
3. The speed sensor (or it uses ABS system if equipped) – NSF hub held on by 10mm bolt and rust
4. The steering controller switch – mounted to 4WS rack N/S
5. 2 relays in engine bay, N/S against wing in middle (1 for main motor, 1 for backup motor)
6. Main motor – N/S of rack
7. Backup motor – O/S of rack

## Common 4WS Problems

1. 4WS light on and back wheels don't turn at all – not so common
2. 4WS works at standstill but light comes on when moving off (usually when turning) – not that common
3. Wheels turn in the same direction all the time, making slow corners very unpleasant – very common
4. Wheels turn in opposing direction all the time, causing you to fall off the road into a bush – rare

The failsafe seems to be number 3, presumably so that if you are moving at high speed, it won't upset your driving too much.

## Main Component Failures

### Speed Sensor

- Located on the N/S/F hub (on non-ABS cars)
- Breaks frequently, causing problems 3 & 4
- If you get code 41, chances are your sensor has failed
- Replacement is difficult due to seizing
- Replacement sensor costs around £120 from Mr T
- A possible alternative: 1992 Toyota Camry ABS sensor (requires modification)

### Backup Motor

- Smaller of the two motors
- Located on the right side when looking from the back of the car
- Similar to windscreen wiper motors but smaller

#### Accessing the Motors

1. Look under the car at the back, towards the rear axle area
2. Remove the metal cover plate in the center of the axle (4 12mm bolts)
3. Remove wiring channel (2 10mm bolts)

#### Removing the Motors

1. Unplug the 2 motor connectors in the boot
2. Remove the 4 bolts/screws holding the motor hub
3. Check if the rack is jammed
4. Test the motors using a 12V battery

#### Motor Issues

- Common problems: seized shaft, worn brushes, damaged windings
- Repairs should be done by professionals
- Replacement hub unit with 2 motors costs around $2000 from Toyota

### Steering Control Sensor

- Tells the system where the back wheels are
- It's a potentiometer
- Needs re-centering if replaced or disturbed

#### Adjusting the Sensor

1. Center the rear rack
2. Measure resistance between pins
3. Adjust sensor position by twisting

### Relays and ECUs

- 2 relays in the engine bay (rarely fail)
- 2 ECUs on the N/S/R wing behind the carpet (replacement might be the only option if faulty)

## Wiring

- Extensive wiring for the 4WS system
- If all else fails, tracing every wire or obtaining another loom might be necessary

## Disabling the System

- Can be done by locking the rack up or replacing back-end components
- Some success reported by centralizing the rack and disconnecting both motors (use at your own risk)

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*Note: This guide is based on personal experiences and extensive web research. Information may be updated as new discoveries are made.*

Source: 4WS Overview - Wiki (celica-club.co.uk)
Author: Rammers