Troubleshooting — General Information and Preliminary Checks (BMW 7 Series E38)

Please also refer to Section Troubleshooting in Introduction.

The ignition and fuel systems are interconnected components of the engine management system, so some of its components may also perform functions related to the fuel system.

General information

1. The ignition and power supply systems have a common diagnostic system designed to store fault codes (DTC) and perform diagnostics. When a failure is detected, the control unit records the corresponding DTC code in memory, which can be read using a special scanner.

2. Reading the information stored in the ECM memory in most cases allows you to determine the causes of engine malfunctions. Analyzing the read information using the code list (see Specifications) allows you to localize the source of failure at the level of a specific element or its electrical wiring circuit.

Visual inspection of the wiring and connectors is not enough - be sure to read the information stored in the control unit memory!

Preliminary checks

1. If a malfunction occurs shortly after servicing of a component, first of all, the component and its adjacent components should be carefully examined – it is possible that the cause of the failure is related to an elementary violation of the quality of the contact connection.

2. When searching for the causes of engine malfunction (for example, a drop in the developed power) it always makes sense to check the compression in the cylinders (see chapter Engine). Also make sure that the air and fuel filters are replaced according to the maintenance schedule (see chapter Vehicle settings and routine maintenance).



3. Do not forget to clear the control unit memory after reading the fault codes and making the appropriate corrections.

4. Open the hood and check the reliability of the fastening of the wire tips to the battery terminals, make sure there are no signs of oxidation of the terminal connections. If necessary, take appropriate measures to eliminate the problem, replace the failed components. No less carefully examine the condition of the grounding buses and their terminal connections - the contact surfaces of the corresponding mass elements (powertrain/body panels) must be absolutely clean and free from traces of corrosion.

5. Carefully inspect all visible electrical wiring inside the engine compartment, check the reliability of the contact connections. Replace electrical wiring that shows obvious signs of damage, making sure that the harnesses are laid correctly; if necessary, tighten the loose fasteners of the units on which the insulation has rubbed off.

The risk zone is always the sections of electrical wiring that pass near components that were serviced most recently.

6. It should be remembered that the conductive wires of the electrical wiring may be damaged in the absence of signs of damage to the insulation - in such a situation, an external inspection will not give positive results. Such damage may occur as a result of pulling out the wires, or when their routes are violated.

7. Damaged wiring can be repaired by soldering the shunt core into the broken section – soldering ensures reliable electrical contact. To repair the insulation, use insulating tape or place a piece of heat shrink tubing on the wire. The best way (although not the cheapest) the way to eliminate all failures associated with damage to electrical wiring is to replace the faulty wire.



8. After completing the repair/selecting a replacement, ensure that the appropriate harnesses are routed correctly, paying particular attention to sections of the routes that pass near heated surfaces and moving components in the engine compartment. Ensure that the harnesses are securely fastened to all intermediate fasteners provided.

9. Check the condition of all accessible terminal connections, check the reliability of the fastening of the electrical wiring contact connectors. If traces of corrosion are found on the inner surface of the connector, (white or green deposits, rusty coating), and if excessively dirty, remove the connector from the corresponding terminal and clean thoroughly, using a special spray if necessary. Seriously damaged connectors are subject to replacement, in some cases together with the wiring harness.

10. After cleaning the connector from corrosion, pack it with preservative grease before installing it in place.

11. The vehicles discussed in this Manual use a crankshaft position (CKP) sensor, which determines the TDC position of the piston of the first cylinder. Excessive contamination or dustiness of the sensor may cause misfires.

12. Carefully inspect the hoses and tubes of all vacuum lines in the engine compartment. Check the tightness of the fastening clamps, make sure there are no deformations, cracks, cuts, delamination or other physical damage to the hoses and tubes. Carefully examine the fittings for signs of leaks (see chapter Vehicle settings and routine maintenance).



13. Assess the condition and check the patency of the PCV system hoses. Excessive contamination or obstruction of the hoses will result in instability of engine speed, especially at idle.

14. Moving from the fuel tank to the fuel distribution line (through the fuel filter) along the fuel lines, carefully examine the condition of the fuel lines. Pay special attention to the joints of the tubes, where cracks most often form, through which leaks begin to develop. Replace damaged sections of the fuel lines.

15. Check the condition of the air cleaner filter element. An excessively dirty filter can significantly increase the total aerodynamic resistance of the intake air tract, which directly affects the power developed by the engine. Replace the filter element if necessary.

16. Start the engine and let it idle.

When performing any work in the engine compartment with the engine running, exercise extreme caution - try not to touch the hot surfaces of the power unit and exhaust system, do not allow hair or clothing to get into moving components (cooling fan, auxiliary drive belt)!

17. Moving from the air intake to the air cleaner and further to the throttle body, make sure there are no signs of air leaks developing in the intake tract. You can use a soap solution to identify the sources of leaks. Make the necessary corrections.

18. Drive the car onto a lift and examine the condition of the exhaust system components. Make sure there are no signs of developing leaks - the easiest way to detect leaks in the exhaust tract is to plug its outlet - a characteristic whistle and smoke will help to localize the damaged area. Tighten loose clamps/replace failed gaskets, replace damaged sections.



19. At the final stage of testing, with the engine running, pull the contact connectors of its electrical wiring one by one - a change in the nature of the engine's operation will indicate poor contact quality - make the necessary corrections, replace the faulty sections of the electrical wiring.

20. If, during the preliminary checks, it is not possible to identify the cause of the engine malfunction, the vehicle should be taken to a service station for more thorough diagnostics using special equipment.

Original publication posted on the website: «BMWMan.ru»