second BMW M5 2000 E39 Central Body Electronics ZKE Manual

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Central Body Electronics ZKE III
Seat Heating Operation (from 99 MY)
Principle of Operation
The front seat heaters are adjustable through three ranges of
heating output temperature.
Pressing the respective seat heater button once provides
stage 1:
• All three LEDs illuminate and the heating elements are provided regulated output current
producing a seat temperature of 111
OF.
Pressing the button a second time provides stage 2:
• The top LED switches off and the heating elements are regulated to an output tempera-
ture of 102
OF.
Pressing the button a third time provides stage 3.
• The top and middle LEDs are off and the heating elements are regulated to an output tem-
perature of 95
OF.
The SZM monitors the seat heating element temperature via an NTC feedback signal to
regulate the output current which maintains the seat temperature.
Seat heating is switched off by pressing the button a fourth time,
pressing and holding the
button for more than 1 second or when the ignition is switched off.
System Components
Carbon Fiber Heating Pads:In each seat is a two
section heating pad wired in parallel. The heating pads
are resistors which when powered produce radiant
heat.
The seat base heating element also contains a temper-
ature sensor for feedback to provide the temperature
regulation output control.
KL31
KL15
TEMPERATURE
SENSOR
615200139.eps

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Central Body Electronics ZKE III
Center Console Switch Center (SZM): From 1999 MY E38, E39 and E53 vehicles are
equipped with a SZM to control the front seat heating and provide a diagnostic interface
with the DISplus/MoDiC via the K BUS.
The SZM directly controls:
• Front Seat Heating
• Rear Window Roller Blind
SZM also provides a unitized switching center
for:
• Park Distance Control (PDC)
• Dynamic Stability Control (DSC III)
• Electronic Damper Control (EDC).
The switch signal output for these systems is a direct output signal. All diagnosis functions
are carried out through their respective control systems.
SZM Monitoring of Seat Heating
Battery Voltage:The SZM switches current supply to the heating elements off when bat-
tery voltage drops below 11.4 volts. However, the heating stage LEDs remain on.
Regulated output current resumes when battery voltage raises above 12.2 volts for more
than 5 seconds.
SZM Internal Temperature: The power output stages for the seat heating elements gen-
erate a considerable amount of heat when in stage 1 operation. The SZM monitors it’s own
internal temperatures and reduces the heating output when internal temperatures rise to a
temperature of 185
OF or switches it off completely above 203OF. As with battery voltage
monitoring, the heating stage LEDs remain on when these temperatures are exceeded.
Fault Monitoring:The SZM monitors the temperature sensors and heating mats for faults.
Detected faults are stored in the SZM. Fault Symptom Troubleshooting in conjunction with
stored faults will initiate the diagnostic paths using the DISplus/MoDiC. The following faults
can be recognized:
• Shorts or opens in the wiring circuits.
• Shorts or opens in the temperature sensors.
• Open in heating element.
If a short is detected in the temperature sensor, the seat heating is switched off to prevent
overheating. The Stage LEDs are also switched off with this fault present.

Principle of Operation
Control logic (example E38) includes:
• Servotronic control electronics active with KL R being switched "ON" - ensure no delay
in operation if engine is started and vehicle is immediately driven.
• Plausibility check for speed signal - the control electronics monitor both the Speed sig-
nal "A" from the IKE and the vehicle speed signal on the K-Bus.
• The ability to detect both acceleration and deceleration from the two speed signals - the
speed signal from the IKE is updated every two seconds.
• The servotronic assist is reduced gradually when the vehicle is under acceleration.
• The servotronic assist is adopted to the lower direct reading during decel or braking.
Electric/electronic failures with the servotronic system will result in the following:
• Power/electronic failure of the control module or solenoid - steering assist the same as
high speed driving (increased effort).
• Vehicle speed signal missing - control module retains the assist mode in effect when the
speed signal was lost.
• Speed signal implausible - steering assist the same as high speed driving (increased
effort).
The GM also provides the diagnostic “gateway” to the Servotronic status and Component
Activation via the DISplus/MoDiC.
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Central Body Electronics ZKE III

Battery Status
The GM monitors KL R on a dedicated circuit. If the ignition is switched on and detected
via the KL R circuit but the GM does not receive KL R status via the K Bus, the GM mon-
itors the KL R voltage level. If after an additional 0.3 seconds there is no K Bus activity, the
GM initiates an emergency running program.
A substitute value for vehicle speed is used to allow the GM to operate certain functions.
The emergency running program will terminate if the GM detects a vehicle speed or KL R
status via the K bus.
Diagnosis/Troubleshooting
The GM contains an EEPROM fault memory. Diagnosis and troubleshooting is carried out
with the DISplus or MoDiC. The diagnostic link is through the Instrument cluster over the K
bus to the GM.
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