brake BMW 5 SERIES 1985 E28 Cruise Control

CRUISE CONTROL WITH ELECTRIC ACTUATOR

The electric actuator type cruise control system was intro-

duced on the BMW 733i and 528e models in 1982. From 1983 all

six-cylinder models will use this type.

The system is designed to operate at between 20 and approximately

90 mph. An electronic control unit (E.C.U.) controls an

electric actuator which maintains the desired road speed via

the throttle linkage.

Driver control is through a three-function switch operated by

a lever mounted on the right side of the steering column be-

hind the wiper lever.

Pushing the lever forward in the CONST position engages the

system and the car will accelerate until the lever is re-

leased. The E.C.U. contains a memory circuit which will hold

the speed that exists when the lever is released from the

CONST. position. Momentary operation of the lever in the CONST.

position will also cause engagement and lock the prevailing

speed into the memory.

Cruise control may be disengaged in any of five different

ways; momentarily moving the control switch up or down to OFF,

applying the foot brake, shifting the automatic transmission to

neutral, depressing the clutch, or whenever the actual speed

drops more than 15 mph below the memory speed.

Following disengagement, the car can be returned to the pre-

viously selected speed by pulling the control lever to RESUME.

The memory circuits in the E.C.U. are reset whenever the

lever is moved to CONST, but the only time the memory is cleared

is when ignition is turned off.

The E.C.U. receives a processed signal from the electronic

speedometer, which is equivalent to actual road speed. Con-

sequently, speedometer problems will affect cruise control.

ACTUATOR

CLUTCH SWITCH
BRAKE SWITCH

CRUISE CONTROL SCHEMATIC

(ELECTRIC ACTUATOR)
OFF

61-09/1
CABLE

GAS LINKAGE

BRIDGE

(AUTOMATIC)

ECU

SPEEDO

OFF

REED SWITCH

RESUME
CONST.
R

N

D
2
1

P

Test at ECU Plug

Component/Circuit
Result

4. Ignition on—check volt-

age at Terminal #5.
Control switch RESUME.
Move lever to RESUME.

Voltage jumps 0 to 12V.

If not, check wiring and

switch.

5. Measure resistance Term-

inal #3 to ground. (Auto

transmission in neutral.)

(Ignition off.)
A.) Automatic Trans-

mission

B.) Manual Trans-

mission
A.) Approximately 4

B.) < 1

6. Apply voltage to term.

#8 and ground term. #9.
Actuator solenoid

(Clutch)
Listen for click in actuator

7. Measure resistance

Terminal #8 to ground.
Actuator and clutch

switch.
Resistance approx. 30

Press clutch pedal, then

resistance = oo

If not, check wiring, clutch

switch, and brake lights.

8. Apply voltage to term.

#13 and ground term. #25.
Actuator motor

Listen for motor running.

9. Measure resistance

Terminal #24 to Terminal

#23.
Actuator potentiometer.

Resistance approx. 3000

If not, check wiring/

replace actuator.

10. Measure resistance

Terminal #23 to ground.
Ground
Resistance = 0

If not, check wiring and

ground.

11. Measure resistance

Terminal #26 to ground.
Actuator.
Resistance approx. 3000

If not, check wiring/

replace actuator.

12. Measure voltage at

term. #9 (Ignition on)
Brake light switch
0 Volts then depress brake

pedal voltage = 12V.

61-09/3

FOR CRUISE CONTROL TO BE ENGAGED

PIN 9 MUST SENSE GROUND THROUGH

STOPLIGHTS.

WHEN BRAKE SWITCH IS CLOSED OR

CLUTCH SWITCH IS OPEN, GROUND IS

ELECTRONICALLY REMOVED.

CRUISE CONTROL ELECTRICAL SCHEMATIC
BRAKE

SWITCH

CLOSED WITH BRAKE

PEDAL DEPRESSED
POWER

DISTRIBUTION

BOX

CLUTCH

SWITCH

OPENS WHEN

CLUTCH PEDAL

IS DEPRESSED
POWER

DISTRIBUTION

BOX

AUTOMATIC

TRANSMISSION

RANGE SWITCH
AUTOMATIC TRANSMISSION

CRUISE

CONTROL

SWITCH

C210

CRUISE CONTROL

CONTROL UNIT

TRANSMISSION

RANGE

DISPLAY

TO THROTTLE

VALVE
FEEDBACK

POTENTIOMETER
INSTRUMENT

CLUSTER

CRUISE

CONTROL

ACTUATOR

CLUTCH

SOLENOID
CANCEL RESUME ACCELERATE/

SPEED SET SPEED

CONTROL INPUTS
INSTRUMENT

CLUSTER

MANUAL

TRANSMISSION
IDLE

SPEED

CONTROL
FUSE 6

8 AMP

POWER

DISTRIBUTION
POWER

DISTRIBUTION

ACCELERATE/

SET
OFF RESUME
OFF
S217 C206 S309 C301
.75 GN/WT

.5 VI/WT C210 GN/WT

CLUTCH CONTROL CONTROL MOTOR CRUISE

OUTPUT OUTPUT ENABLE

SEE DASH LIGHTS
GROUND
"N"

OUTPUT

BAND
1.5 GN/WT

1 GN/WT
11

1 GN/WT
.75 GN/WT

.75 GN/WT
1

.75 8U/3R

.75 BU/BR
S234
3

15

1

2

D

6
N
R
P

S
W
0

GN
BU

.5 YL
.5 GN

.5 BU

4
5
SPEEDOMETER

SOLID STATE

2

C8

.5 BU/YL
CRUISE CONTROL

CONTROL UNIT

POWER INPUT
.5 VI/WT
C250

STOP LIGHTS
.5 GN/RD

.5 GN/RD
MANUAL

TRANSMISSION
AUTOMATIC

TRANSMISSION
C208

.5 GN/RD
C208
61-09/5

S224
.5 GN/RD
.5 GN/RD
9

G200
.5 BR
SPEEDOMETER
.5 VI/WT
1.5 VI/WT

S241
FUSE 12

8 AMP

.5 VI/WT

VEHICLE SPEED

INPUT

CRUISE

ENABLE

.75

BU/BR

C8
GROUND
FEEDBACK

REFERENCE
FEEDBACK

INPUT
SOLID STATE

24

26

.5 GY/RD
.5 GN/YL

4

.5 RD
7

.5 YL

.5 BR

3

S233
(-)

12

16

C1
C6
.5 BR

.5 BR

G200
.5 BR
.75 BU/BR

6

7
.75 BU/BR

.5 BU
C209
.5 BU/WT

2
3

G200
13

.5 BK

5

.5 BK
.5 GN
.5 WT

.5 WT
CONTROL

MOTOR
1

CRUISE CONTROL

The BMW cruise control is designed to operate between 20

and approximately 90 mph. An electronic control unit (E.C.U.)

controls a vacuum operated servo unit which actuates the

throttle linkage to maintain the required road speed.

Drive control is through a three function switch operated

by a lever mounted on the right side of the steering column

behind the wiper lever.

Pushing the lever forward in the CONST position engages the

system and the car will accelerate until the lever is

released. The E.C.U. contains a memory circuit which will

hold the speed that exists when the lever is released from

the CONST position. Momentary operation of the lever in the

CONST position will also cause engagement and lock the

prevailing speed into the memory.

Cruise control may be disengaged in any of five different

ways: momentarily moving the control switch up or down to

OFF, applying the foot brake, shifting the transmission to

neutral, or whenever the actual speed drops more than 7 mph

below the memory speed.

Following disengagement, the car can be returned to the

previously selected speed by pulling the control lever to

RESUME.

The memory circuits in the E.C.U. are reset whenever the

lever is moved to CONST but the only time the memory is

cleared is when ignition is turned off.

SPEEDO CABLE

SIGNAL GENERATOR
OFF

CONST.

CRUISE CONTROL SCHEMATIC

61-08/1
SERVO

CABLE

VACUUM
VENT
GAS LINKAGE

BRAKE SWITCH

P R N D 2 1

ADAPTER

ECU

RESUME

OFF

REED SWITCH
SPEEDO

CRUISE CONTROL SYSTEM TESTS - 733i (VACUUM SERVO)

A. Vacuum - Check fit and condition of all vacuum and vent lines.

B. Electrical

TEST AT ECU PLUG
COMPONENT/CIRCUIT

RESULT

1.
Measure
resistance

across term. 1-12

push car min. 2 feet
Reed switch in differen-

tial
and
wiring.
Resistance changes 0 to oo

to 0, etc. If not, check

wiring and switch.

2. Ignition on. Check

voltage at term. 5.
Power supply.

Voltage - 12V. If not, check

wiring.

3. Start car. Jumper

term. 5-3 and then

12-7 momentarily.
Servo
Servo should activate and raise

engine speed. If not, check

wiring and Servo.

4a. Ignition on (not

running). Check

voltage at term. 6.

b. Ignition off. Check

resistance terminal 6

to ground.
System disconnect

circuit.

Adaptor ground.
No voltage. Push brake pedal

then voltage = 12V, or trans.

to 'N' and voltage = 12V. If

not, check wiring, switches,

and adaptor.

Reading approx. 20 to 150

Now reverse leads and reading

must remain between 20 and

150. If reading is at oo

with either hook up check

adaptor grounding or replace

adaptor.

5. Ignition on. Check

voltage at term. 8.
Control switch OFF.

Move lever to OFF. Voltage

drops from 12 -> 0 volts. If

not, check wiring and switch.

6. Ignition on. Check

voltage at term. 9.
Control switch CONST.
Move lever to CONST. Voltage

jumps 0 to 12 volts. If not,

check wiring and switch.

7. Ignition on. Check

voltage at term. 10.
Control switch RESUME
Move lever to RESUME. Voltage

jumps 0 to 12 volts. If not,

check wiring and switch.

If these electrical tests are OK, then change the control unit if the system does not

operate correctly.

61-03/2

CRUISE CONTROL ELECTRICAL SCHEMATIC 733IA

61-08/3
GN-green BR-brown

WS-white RT-red

BL-blue VI-violet

GE-yellow

1. Control Unit (ECU) 5. Adaptor 9. Fuses

2. Reed Switch 6. Trans. Lights (Instruments) 10. Relief Relay

3. Servo 7. Brake Switch 11. Ignition Switch

4. Control Switch 8. Brake Light 12. Battery

CRUISE CONTROL SYSTEM TESTS - 633CSi (VACUUM SERVO)

A, Vacuum - Check fit and condition of all vacuum and vent lines.

B. Electrical

TEST AT ECU PLUG
COMPONENT/CIRCUIT
RESULT

1. Measure A/C voltage

across terms. 11-12.

Car on hoist in gear

and running.
Signal Generator and

wiring.
10 mph approx. 0.7 V A/C

20 mph approx. 1.4 V A/C

30 mph approx. 2.1 V A/C

40 mph approx. 2.8V A/C

2. Ignition on. Check

voltage at term. 5.
Power supply.

Voltage - 12V. If not,

check wiring.

3. Start car. Jumper

term. 5-3 and then

12-7 momentarily.
Servo.

Servo should activate and

raise engine speed. If

not, check wiring and Servo.

4a. Ignition on (not

running). Check

voltage at term. 6.

b. Ignition off. Check

resistance terminal

6 to ground.
System disconnect

circuit.

Adaptor ground.
No voltage. Push brake pedal

then voltage = 12V, or trans.

to 'N' and voltage = 12V. If

not, check wiring, switches,

and adaptor.

Reading approx 20 to 150 .

Now reverse leads and reading

must remain between 20 and 150

If reading is at oo with either

hook up check adaptor grounding

or replace adaptor.

5. Ignition on. Check

voltage at term. 8.
Control switch OFF.
Move lever to OFF. Voltage

drops from 12 -> 0 volts. If

not, check wiring and switch.

6. Ignition on. Check

voltage at term. 9.
Control switch CONST.
Move lever to CONST. Voltage

jumps 0 to 12 volts. If not,

check wiring and switch.

7. Ignition on. Check

voltage at term. 10.
Control switch RESUME.
Move lever to RESUME. Voltage

jumps 0 to 12 volts. If not,

check wiring and switch.

If these electrical tests are OK, then change the control unit if the system does not

operate correctly.

61-08/4

CRUISE CONTROL ELECTRICAL SCHEMATIC 633CSiA

61-08/5
1. Control Unit (ECU) 5. Control Switch 9. Fuses

2. Signal Generator 6. Battery 10. Relief Relay

3. Ignition Switch 7. Adaptor 11. Brake Light

4. Servo 8. Trans. Lights 12. Brake Switch
GN-green BR-brown

WS-white RT-red

BL-blue VI-violet

GE-yellow