ECU BMW 5 SERIES 1981 E28 Cruise Control

ACTUATOR

CLUTCH SWITCH
BRAKE SWITCH

CRUISE CONTROL SCHEMATIC

(ELECTRIC ACTUATOR)
OFF

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CABLE

GAS LINKAGE

BRIDGE

(AUTOMATIC)

ECU

SPEEDO

OFF

REED SWITCH

RESUME
CONST.
R

N

D
2
1

P

CRUISE CONTROL SYSTEM TESTS

(ELECTRIC ACTUATOR)

Use BMW Service Test 2013 to check function of system

as follows:

Program: Enter M (Multimeter)

Enter 13 (Frequency out)

Enter 110 (Hz)

Press

Enter 02 (U. AC.)

Press

1. Detach the differential reed switch plug and attach frequency

out (+) to brown/red wire and frequency out (-) to brown

wire.

2. Turn on ignition.

3. Speedometer should show approximately 50 mph.

4. Engage cruise control and monitor the actuator. (It should

pull the throttle open.)

5. If cruise control does not engage, check for A.C. voltage on

E.C.U. plug terminal #6. (It should be approximately 4.0

volts.)

6. Check plug connections on back of instrument cluster.

7. If system is still inactive, perform the following tests:

Test at ECU Plug
Component/Circuit

Result

1. Ignition on—check volt-

age at Terminal #1.
Power supply

12 Volts. If not, check

wiring and fuse.

2. Ignition on—check volt-

age at Terminal #2.
Control switch OFF

Move lever to OFF. Voltage

drops from 12V to 0V. If

not, check wiring and

switch.

3. Ignition on—check volt-

age at Terminal #4.
Control switch CONST.

Move lever to CONST.

Voltage jumps 0 to 12V.

If not, check wiring and

switch.

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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.

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SPEEDO CABLE

SIGNAL GENERATOR
OFF

CONST.

CRUISE CONTROL SCHEMATIC

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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.

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CRUISE CONTROL ELECTRICAL SCHEMATIC 733IA

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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.

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CRUISE CONTROL ELECTRICAL SCHEMATIC 633CSiA

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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