Specifications

Testing Testing Bus Systems

When the Rest feature is activated, all of the IHKA functions are operable. This includes the

blower speed, air distribution control and temperature settings. With the ignition switched off, the

Rest feature is in a preset operating mode: the blower fan runs at medium speed and the

temperature is set to allow maximum heat.

The Rest feature can only be switched off under the following conditions:

• Ignition switched on

• Battery voltage less than 11.4V

• Rest button pressed while system is on

• Coolant temperature less than 86°F (30°C)

• After 15 minutes time period

4.6.4 IHKA Substituted Values

Substituted values are operating parameters that are programmed into the control module

nonvolatile memory. The substituted values are used by the IHKA control module to maintain

system operation if a sensor or circuit fails. This may not be true for the evaporator temperature

sensor or the exterior temperature sensor which have a substituted value below the cycling point

of the AC compressor (AC system will not operate).

Table 4-14 lists substituted values, and Table 4-15 lists temperature sensor resistance values at

an ambient temperature of 77°F (25°C).

4.7 Testing Bus Systems

BMW began using data bus systems in 1991 on the E31 8 Series. By 1993, most models were

using CAN bus systems for the powertrain control module, and some models added ABS.

Table 4-14 IHKA substituted values

Temperature Sensor Working Range Substituted Value

Heat exchange sensor 41–255°F (5–124°C) 131°F (55°C)

Evaporator sensor 50–86°F (10–30°C) 32°F (0°C)

Interior temperature sensor 50–104°F (10–40°C) 68°F (20°C)

Exterior temperature sensor Signal sent over the K Bus 32°F (0°C)

Coolant temperature sensor Signal sent over the K Bus 212°F (100°C)

Table 4-15 IHKA temperature sensor resistance values

Sensor Resistance Fault Limit

Heat exchange sensor 9K Ohms ±2% Greater than 257°F (125°C)

Evaporator sensor 9K Ohms ±2% Greater than 248°F (120°C)

Interior sensor 10K Ohms ±2%

Greater than 192°F (89°C) or

Equal to or less than 115°F (46°C)