A/C - No Or Insufficient Heat When Temp. Set To MAX
SI B64 03 11Heating and Air Conditioning
March 2011
Technical Service
SUBJECT
No or Insufficient Heat when the Temperature Is Set to Maximum
MODEL
E90, E91, E92, E93 (3 Series)
SITUATION
There is no or insufficient heat when the temperature is set to maximum. After the vehicle has reached operating temperature, the temperature of the air coming out from all the vents is not hot.
CAUSE
This could be caused by various issues, such as:
^ Coolant insufficiently filled
^ Clogged heater core or blocked radiator and/or hoses
^ Mixing flaps/stratification flap operating incorrectly
^ Ventilation temperature sensor
^ Footwell temperature sensor faulty
^ Interior temperature sensor faulty
^ Water valve not functioning correctly
^ IHKA (Integrated Heating and Air Conditioning, automatic) sending incorrect signal
PROCEDURE
Perform the following steps:
1. Verify the performance of the heater using a thermometer to measure the air temp at the vents (Defrost and Footwell). Compare to a known good vehicle. If heater performance is insufficient when compared to a similar known good vehicle, proceed to the next step.
2. Perform a vehicle test using ISTA (Integrated Service Technical Application) and complete all related test plans if fault codes are stored.
3. The temperature comparison in steps 4 and 5 must be done as follows:
^ While the vehicle is idling in the shop
^ During a test drive
4. Check the engine and radiator temperature and compare readings to a similar known good vehicle (ISTA ECU functions).
5. Using a thermometer, compare the vent temperature readings to that of a similar known good vehicle. This can also be done via Function Structure/Heating and air conditioning functions/Start search.
^ Select test plan AT6450_KAEKL from the list and click Display.
^ Option 5 - Display system values
6. Check the auxiliary water pump for correct operation (ISTA ECU component activation). If equipped with a water valve, disconnect the electrical connector from the water valve and monitor the vent temperature, as stated in step 5.
7. If the water valves and water pump are operating correctly, but there is still insufficient heat, a visual inspection of the heater core is needed.
Caution:
Allow the vehicle to cool down before proceeding to the next step.
8. Disconnect the heater hoses entering the passenger compartment (at the bulkhead). Flush the heater core using a water hose. This must be done in both directions. Collect the dispensed water in a bucket and check for contaminants such as sand, etc.
9. If no contaminants are found during backflushing of the heater core and the water flow is good, retest the heater function during a test drive. Verify all temperatures in steps 3, 4 and 5. If the heater is working as designed, release the vehicle.
10. If contaminants are collected or the water flow through the heater core circuit is restricted, proceed to the next step.
11. Refer to REP "6411208 Replacing Heat Exchanger" for replacing the heater core.
12. If further assistance is required, submit a PuMA case.
Note:
Search for related test plans under Function structure/Body/Heating and air conditioning functions/Start search. This will display all available test plans if no faults are stored.
WARRANTY INFORMATION
This service information bulletin is intended to provide technical diagnostic and/or repair information.
Claims that result from the repair of a verified defect are to be processed following established warranty policies and procedures.
Refer to the KSD2 to code the repair(s) performed as determined by the diagnosis.