Diagnosis/troubleshooting
Anti-lock brake system
System ABS 5.3 and
System ABS/TC 5.3

---

Anti-lock brake system, diagnosis
Important information about ABS 5.3 and ABS/TC 5.3
General

The Porsche Boxster is fitted as standard with an anti-lock brake system (ABS 5.3).
"Traction Control (TC)" can be obtained on special request on the basis of ABS 5.3. Traction
Control (TC) is a combination of anti-slip control (ASR) and Automatic Brake Differential (ABD).
TC is a further system for increasing driving safety.
ABS 5.3 is optimized with regard to installed volume and weight compared with the ABS 5 (ABS
5 in the 993). Control module (No. 1), hydraulic unit (No. 7), pump motor relay and valve relay
(No. 2) of ABS 5.3 and ABS/TC 5.3 are a unit that is positioned next to the master brake cylinder.

Diagnosis and system checks on both systems are carried out with the Porsche System
Tester 2.
Differences between ABS 5.3 and ABS/TC 5.3

ABS 5.3 = 3-channel system
ABS/TC 5.3 = 4-channel system
The essential distinguishing features between ABS and ABS/TC are:

−
Number of brake lines at intermediate piece
ABS 5.3
=
3 brake lines
ABS/TC 5.3 =
4 brake lines
−
TC OFF switch for switching driving stability control on and off is not available on vehicles
with Solo ABS (ABS 5.3).

---

TC (ASR/ABD) MIL and
TC (ASR/ABD) function light
(Information light) in vehicles with ABS/TC. These lights are lit when the ignition is switched
on (lamp check).
In vehicles with ABS 5.3 (Solo ABS) these lamps are not fitted in the instrument cluster.
A figure showing the warning (MIL) and function lights

ABS 5.3 (3-channel system) system description ABS operation
The ABS control module receives a signal from the stoplight switch and the AC voltage signals
from the four speed sensors. These signals are converted into digital wheel-speed signals inde-
pendently of each other by two microprocessors. The wheel slip (approximately proportional to
the computed vehicle reference speed)is formed from these wheel-speed signals.
If vehicle deceleration and excess slip are detected at a wheel, the pressure-holding phase is
initiated as the first step, i.e. the inlet valve for the relevant wheel is closed to prevent a further
increase in pressure. If in spite of the pressure being held constant the wheel tends to continue
to locking up, the pressure in the brake cylinder reduced. For this purpose, the outlet valve is
opened and the brake fluid is pumped back to the brake master cylinder via the return pump
(pressure-reduction phase), until the wheel turns again. Then, depending on the control cycle,
further appropriate cycles are initiated.
This function or the input signals are continuously monitored. If a fault is detected, the
control module switches the ABS function off, switches on the ABS MIL and stores the
fault in a non-volatile memory in the control module.

In addition, whenever a trip is begun and a speed of 6 km/h is exceeded, a test program is
started. The solenoid valves and the pump motor are electrically actuated and checked. If a
fault is detected, the control module switches the ABS function off, the ABS MIL is switched on
and the fault is stored.

---

Diagram: ABS 5.3 (3-channel system)

»a-96
1 - ABS control module

2 - Brake unit (brake booster with tandem master brake cylinder)

3 - ABS hydraulic unit * (3 hydraulic outputs)

4 - ABS speed sensors

5 - Central Information System

6 - Brake proportioning valve (lx)
7 - Brake light
8 - Stop-light switch
9 - ABS MIL (yellow)
A = Front-axle braking circuit
B = Rear-axle braking circuit
C = Parking brake cable deflection box
Control module, hydraulic unit, pump motor relay and valve relay form a unit, which is located next to the
master brake cylinder.

---

ABS/TC 5.3 (4-channel system) system description
Note
Traction Control (TC) represents an extension of the ABS system and is a combination of anti-slip
control(ASR)and Automatic Brake Differential (ABD).
TC prevents spinning of the drive wheels when moving off and accelrating. Driving stability and
traction are improved over the entre speed range.
Traction Control (TC) is ready for opera, on when-ever the engine is stared.
The TC information lamp in the instrument panel is lit during a control process and warns that the
driving style must be mashed to road conditions.
Function.

Driving stability control:
If Traction Control (TC) detects that a certain speed difference between the wheels has been
exceeded (wheel-spin), engine power is automatically reduced.

Brake control:
In addition to reducing the engine power (driving stability control), the TC (via the ABD) brakes
the drive wheel that is spinning.
Since this control requires the drive wheels to be individually controlled the ABS/'I'C system is a
4-channel system.
Switching off driving stability control

Press the "TC OFF" logo of the rocker switch. Driving stability control cannot be switched off
during a TC control process (information light on).
One-sided wheel speed on the drive axle is further prevented by brake control up to a speed of 1
O0 km/h.
Driving stability is not monitored, since the drive wheels can start to spin at the same speed (slip).
With driving stability control switched off, the TC MIL in the instrument panel and the indicator light
in the rocker switch are lit.
It can be advantageous to switch off driving stability control:
-on a loose surface and in deep snow
- when "rocking" the vehicle free
-when using snow chains.
Switching driving stability control back on *

Press the indicator light in the rocker switch.
Driving stability control cannot be switched on again during a TC control process (information
light on).
Press the switch for at least 0.1 second. Then a further 0.3 seconds will pass until the
routine is complete. Only then is driving stability control switched off or on.

---

Diagram: ABS/TC 5.3 (4-channel system)

1 - ABS/TC control module
2 - Brake unit (brake booster with tandem master brake cylinder)
3 - ABS/TC hydraulic unit * (4 hydraulic outputs)
4 - ABS speed sensors
5 - Central Information System
6 - Brake proportioning valve (lx)
7 - Brake light
8 - Stop-light switch
9 - ABS MIL (yellow)
10 - TC MIL (TC/yellow)
11 - TC function light (green)
12 - DME control module
13 - TC rocker switch (see Page 45 D 10)
A = Front axle braking circuit
B = Rear-axle braking circuit
C = Parking brake cable deflection box

---

*
Control module, hydraulic unit, pump-motor relay and valve relay form a unit, which is located
beside the master brake cylinder.
Component arrangement (ABS 5.3 and ABS/TC 5.3)

---

Function of individual components

1. Control module (ABS 5.3 and ABS/TC 5.3)

This module processes incoming signals and actuates the solenoid valves or/and the return pump
in the hydraulic unit when wheel slip is excessive (see also System description). If the ABS or
ABS/TC switches off when a system fault is detected, it activates the MIL and stores the fault in a
non-volatile memory.

Note

The control module and relay are not supplied individually. In the event of replacement, the com-
plete hydraulic unit must be replaced.
The relays cannot be exchanged.
When replacement is necessary, the complete hydraulic unit must be replaced.
3. Fuses
3a. A 50-A fuse in the current distributor (F1/arrow) protects the return pump and the solenoid
valves.
The current distributor is located under the instrument panel. The fastening points are ac-
cessible from the luggage-compartment side.
Note
3b. The 15-A fuse F 2/9 (field 2, No. 9)on the
central electrical board protects the control module's electrical supply (ABS and
ABS/TC). The arrow points to field 2.

2. Relay

The solenoid valve relay is actuated by the control module(closes) as soon as the control
module receives voltage from the generator (D+ / terminal 61).
As soon as the relay has closed (picked up), battery positive voltage (terminal 30)is present at
the valve coils of all solenoid valves in the hydraulic unit.
If the ABS or the TC (ABD) begins to control, the control module applies negative voltage to the
appropriate valve coil of the valve to be controlled at the appropriate wheel.
The return pump relay is actuated (with a negative voltage) by the control module if required,
and closes.
As soon as the relay has closed/ picked up, battery positive voltage (terminal 30)is applied to the
return pump, which then runs.
On vehicles with Traction Control (TC), the
1 5-A fuse F 2/1 (field 2, No. 1) on the central electrical board protects the supply to the "TC
OFF" rocker switch (switch for switching driving stability control on and off).
4. Speed sensors

The speed sensors provide wheel speed information (speed information for each wheel) to the

---

control module. These speed sensors operate ac-cording to the inductive principle, in which
sinusoidal alternating voltages are genrated in accordance with the number of teeth on a pulse
wheel and at a frequency that is a measure of the wheel speed.

5. MIL and information lights Note

A = TC information light (see Page 45- D 10)
B = TC MIL (see Page 45- D 10) G = ABS MIL (see Page 45- D 10)
Information light for TC (A)
- Lights for a lamp check when the ignition is switched on

Indicates a control process (even when driving stability control is switched off).


MIL for TC (B)
Lights in combination with the indicator light in the rocker switch (TC OFF) for a lamp check when
the ignition is switched on.

In combination with the indicator light in the rocker switch, indicates that driving stability control
is off.

-
Indicates defect: TC is out of order

Lights together with the ABS MIL if there is an ABS fault

6. TC (OFF) rocker switch with light

Switching driving stability control on and off.
The rocker switch has one contact for switching off and another for switching on.
To switch off, press the "TC OFF" logo on the rocker switch. This applies a positive voltage to
the control module while the switch is pressed. This switches off driving stability control. Driving
stability control cannot be switched off during a TC control process (information light on).
When driving stability control is off, the TC MIL in the instrument panel and the indicator light in
the rocker switch are lit. To switch on driving stability control, press the indicator light in the
rocker switch. This applies a positive voltage to the control module while the switch is pressed.
This switches on driving stability control.
Driving stability control cannot be switched back on during a TC control process (information
light on),
Driving stability control is ready for operation, (i.e. is switched on automatically, whenever the en-
gine is started.)

---

MIL for ABS (G)
- Lights up for a lamp check when ignition is
switched on.

If the ABS MIL lights up with the engine
running, the ABS has switched off due
to a fault.7. Hydraulic unit

The hydraulic unit essentially consists of fast-switching electromagnetic valves and a return pump.
Regardless of the pressure in the master brake cylinder, the hydraulic unit can change the fluid
pressure to the wheel brake cylinders (holding or reducing pressure). Increasing the pressure
above that of the master brake cylinder is not possible, however.
The ABS 5.3 hydraulic unit has
three hydraulic outputs (3-channel system) and six electromagnetic valves (three inlet and
three outlet valves).
The ABS / T C 5.3 hydraulic unit has four hydraulic outputs (4-channel system) and ten
electromagnetic valves (four inlet valves / four outlet valves, one switch-over valve and one intake
valve).
The intake and the switch-over valves are required so that the return pump can perform two
tasks:
I.
Return flow to the master brake cylinder
(pressure reduction during ABS control.
II. Supply (pressure increase) to the right.or
left rear-wheel brake cylinder during
TC control (ABD control).
In the case of ABS control at the rear axle, the solenoid valves for both rear wheels are actuated
in parallel (joint control as in Solo ABS control (3-channel system)).

---

Document Outline

• • ÿ
• ÿ
• ÿ
• ÿ

---