Vehicle model: 318i
Year: Dec. 2004
Engine type: L13A3
VIN: LBVEY97044SA41816
Fault phenomenon:
When turning on the air conditioner during driving, the air conditioner is blowing hot air. And it seems that the compressor does not function. The instrument displays that the outside temperature is -40 degrees (See Figure 2). The Air conditioner does not cooling.

Fault diagnosis and analysis:
The vehicle, with electronic control system, has self-diagnosis function. You need to perform the following test according to the instructions below with Fcar diagnostic scanner.
1.Find the location of diagnostic socket (See Figure 3);
2.Connect OBD test head and the main unit with test lines respectively;
3.Connect the diagnostic socket, and turn ignition switch to ON position;
4.Turn on the power of Fcar diagnostic scanner;
5.Enter the menu and select [EUROPE] - [BWM] - [V7.7] - [3 series] - [3’_E90/E91/E92/E93(2004~)] - [Body] - [IHKA integrated automatic heating/air conditioning] - [Read DTC] - [ CE outside temperature sensor] - [Clear DTC] - [DTC is cleared successfully] – [Read DTC] – [System is OK] – [The instrument still displays -40 degrees] – [Turn OFF ignition key] – click [Read DTC] – [ CE outside temperature sensor] occurs again.
It was caused by damage of outside temperature sensor and circuit fault, analyzing according to the DTCs read. The main functions is to check the outside temperature, measure the temperature difference between inside temperature and outside temperature, defrost when it is cold, and control cooling system of air conditioner. After learning about the functions of outside temperature sensor, perform the inspection of outside temperature sensor as follows:
1.Remove outside temperature sensor and heat it with warm water to see if there is any change of thermometer on the instrument.
2.Measure whether the utilization voltage is between 5V——4.1V with multimeter, and check if supply lines communicate properly.
Attention: Power must be OFF when connecting or unplugging the sensors and ECU. Otherwise, electronic control system might be damaged by current produced!
3.Measure whether the resistance is normal with multimeter, between 3.6MΩ and 6.8MΩ. Resistance value varies with the climate. Thus the resistance measured might be different.
4.Under the circumstances of no sensor, a resistance between 3.6MΩ and 6.8MΩ can be used to replace outside temperature sensor temporarily according to the climate, in order to repair the vehicle as soon as possible. This operation must be performed by a specialized person. Otherwise, the electric equipment might be damaged.
Troubleshooting:

Figure 4 Location of outside temperature sensor
Outside temperature sensor

Replace outside temperature sensor (See Figure 4), and clear DTC with FCAR diagnostic scanner. It displays that the DTC is cleared successfully. The system is OK. Start the engine and turn on the air conditioning system. The instrument displays that the outside temperature is 27 degrees. The trouble is solved.
 
 
 
 
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