Condition of the car: A 2003 BMW 530i with a mileage of more than 100,000 kilometres sometimes fails to start. Sometimes it can be started by shaking the gear knob a few times. The test drive with the owner confirmed the malfunction.
Fault diagnosis: There is a certain contingency when the fault occurs. When the fault occurs, the starter does not respond, and the voltage of the battery is normal.
It is preliminarily judged that the starter or the line controlled by it is faulty. So check the starting system of the vehicle when the engine is completely unable to start, as shown in Figure 1.
Check that the starter X6510 has no signal (S-50) when starting, measure the onboard voltage at 14.5V, and it is normal; measure the starter X6150 signal line when the voltage is 0V when starting, and look for the S-50 signal in turn according to the circuit diagram.
First, measure from the ignition switch. When starting, there is a voltage signal of 12V on the 8 pins of X33, which proves that the ignition switch is normal, and the second pin of X1659 of EWS also has a voltage signal of 12V. But there is no voltage when measuring pin 1 of X1659.
EWS is used for the theft insurance of BMW cars and allows starting. The key transmits the data to the EWS control module. If the data is correct, the EWS allows the starter to work through a relay inside the control module.
Besides, a coded enable start signal is sent out through a data wire of the DME. The EWS control module communicates with the key inserted in the ignition switch. If the communication process is normal and the key sends all the data required for identification and permission to start With the control module, the control module can identify whether the key is valid and usable.
If it is valid and can be used, the starter relay in the control module can work, and a coded start signal is sent out through a data wire of the DME.
For cars with automatic transmission, only when the shift lever is in the P and N positions can the vehicle be started through the EWS. The EWS control module receives two signals about the shift lever position: through the wire; through the K bus.
Next, perform a diagnostic test through ISID, and read the fault content: EGS neutral safety switch (P0705), IKE EGS signal line interferes.
Carry out the test plan, operate the transmission shift switch, and sequentially engage the P/R/N/D gears. The fault that the shift lever position P/N gear sometimes cannot start correctly is displayed. Check that the shift lever cable is adjusted normally.
According to the circuit diagram provided by the test plan (as shown in Figure 2), check that the power supply of the No. 31 wire of the transmission X70004 is normal 12.8V, and check that all wires from X70004 to X8532 are normal.
Continue to execute the test plan and check the wire signal S-GL1/GL3/GL4 of the transmission shift switch. When the gear is in the P gear, L1 and L2 should be on-board voltage 12V, and L3 and L4 should be 0V, but the actual measurement in the P gear The value is 0V for L2, 0V for N gear, and normal display for R/D gear.
Disconnect all wires of X8532 on the transmission can be displayed as the disconnected state. The connection adapter supplies battery voltage to all wires of S-GL1, S-GL2, S-GL3, and S-GL4, and the signal wire of each switch can identify the battery voltage, so it is finally judged as an internal failure of the transmission gear switch.
Troubleshooting: The transmission gear switch cannot output the signal correctly so that the gear cannot be displayed correctly. The EWS cannot receive the signal of the P/N gear, and the starter cannot be allowed to start the vehicle. Replace the transmission gear switch, troubleshooting.