No Start Testing
DIAGNOSTIC NOTES
^ Before using this section you should have performed the SELF-DIAGNOSTIC PROCEDURES which verify that the
DME control unit and "CHECK ENGINE" light diagnostic capabilities are operational, as well as no trouble codes were stored.
^ Always use the FLOW OF DIAGNOSIS for proper testing sequence.
^ Certain basic faults can be undetectable by the self-diagnostic system of the DME control unit and in some cases can actually interfere with the self-checking and fault memory operation.
Low battery voltage, for example, can cause erroneous faults to set in control unit fault memories or can cause a system to go "Fail Safe" without setting a fault in memory. On the other hand, system fault memories are cleared whenever the control unit or the battery is disconnected. Therefore, all fault memories should be read prior to any vehicle power interruption or troubleshooting.
COMPLAINT VERIFICATION
Whenever possible the repairing technician should personally verify the complaint. Having experienced the malfunction, the technician is less likely to try to repair non-existent faults.
MALFUNCTION VERIFICATION
Today's sophisticated automotive systems are easily misunderstood, which can lead to repairs that attempt to force a particular system to perform in a way that it was never intended to operate. Therefore, the troubleshooting technician should compare the system operation to the nominal system operation as described in the section DESCRIPTION AND OPERATION. Furthermore, the technician is also encouraged to compare the problem vehicle system operation with a known good vehicle.
PREVIOUS REPAIRS
The vehicle repair history can provide explanations to unusual complaints which seem to elude normal troubleshooting attempts. Incorrect components or unapproved repairs can have subtle influences on seemingly unrelated systems.
BATTERY STATE OF CHARGE
Batteries in a state of partial discharge can have a dramatic effect of DME control units and related components.
POSITIVE BATTERY CABLE INTEGRITY
All B+ connections must be in perfect condition for trouble-free electronic system operation. Refer to ELECTRICAL AND ELECTRONIC DIAGRAMS for B+ interconnects.
FUSIBLE LINK INTEGRITY
Fusible links are employed to prevent possible damage to electrical components and wiring harnesses. These links and their connections must be without dynamic resistance. Dynamic resistance can only be checked using the voltage drop method of testing.
NEGATIVE GROUND CONNECTIONS
As all electrical circuits are a circle, all B- connections must also be checked and verified to be in perfect condition. A poor "common" ground point will cause seemingly unrelated systems to influence one another. High current systems which encounter a poor "common" ground can back feed through other electrical systems causing unusual operation and perhaps inexplicable component failure. As with the B+ side of the electrical system, the ground side should be checked dynamically using the voltage drop technique.
POWER TRAIN CABLE ATTACHMENTS
Metal cables attached to the engine or transmission which appear overheated and/or discolored indicate the need to thoroughly test all ground connections.
POWER SUPPLY RELAYS
Fuel pump and main relays as well as their plug connections can be a source of intermittent operation which will not set a fault in the DME fault memory.
ENGINE REFERENCE/SPEED SENSOR
Monolithic sensors should be checked statically and dynamically. Physical mounting and condition of the sensor and pulse wheel must be assured.
HIGH TENSION COIL AND SECONDARY COMPONENTS WIRING
The secondary ignition system should be checked visibly as well as with a suitable engine analyzer and scope. All components should be examined for tight connections and freedom from carbon tracking, moisture and corrosion.
FUEL DELIVERY AND FUEL RAIL PRESSURE
Fuel delivery must begin at once when cranking and the pressure in the fuel rails must be within specifications. Fuel pressure retention must be maintained between the fuel pump outlet and the pressure regulator after engine shutdown.
VALVE CLEARANCE AND SPARK PLUGS
These two service items, if out of specification, can significantly impair engine performance. Valve clearance should be adjusted "cold" with each piston at top dead center when adjusting the respective valves. Spark plug type, condition and gap must verified according to specification.
AIR/FUEL RATIO
Adaptive engine management systems efficiently compensate for conditions which may affect the combustion process. However, when troubleshooting idle quality or driveability complaints, it is still necessary to consider the following:
^ Injector spray pattern quality
^ Presence of unmetered air leaks
^ Evaporative purge system
^ Excessive engine oil dilution
^ Substandard fuel or unapproved additives
^ Carbon build-up
Relay Location:
1. Check the fuel pump fuse (#11) at the engine compartment fuse box.
2. With the ignition switch in the run (ON) position and the fuel pump relay disconnected, make the following voltage measurements at the relay connector:
Relay Terminal Designation:
Refer to: ELECTRICAL AND ELECTRONIC DIAGRAMS
^ Terminal 6 and ground = Battery If not check the wire to battery power for an open
^ Terminal 8 and ground = Battery If not check the wire to the DME main relay for an open
^ Terminal 6 and terminal 4 = Battery If not check the wire for an open
^ If all voltages are correct, go to step 4
3. With the ignition switch OFF, remove the DME main relay and make the following measurements at the relay connector.
^ Terminal 6 and ground = Battery If not check the wire for an open
^ Terminal 8 and ground = Battery If not check the wire for an open
^ Terminal 6 and terminal 4 = Battery If not check the wire for an open
^ If all of the voltages are correct, replace the DME main relay.
4. With the ignition switch OFF, disconnect the DME control unit connector. Connect the BMW universal adapter or equivalent between the control unit and the wire harness side of the connector. Make the following measurements at the universal adapter. NOTE: If the BMW universal adapter or equivalent is not available, terminals should be CAREFULLY back-probed.
^ Terminal 27 and ground = Battery If not check the wire to the ignition coil for an open
^ Terminal 18 and ground = Battery If not check the wire for an open
^ Terminal 18 and terminal 19 = Battery If not check the wire to ground for an open
^ Terminal 18 and terminal 2 = Battery If not check the wire to ground for an open
^ Terminal 18 and terminal 14 = Battery If not check the wire to ground for an open
^ Terminal 18 and terminal 24 = Battery If not check the wire to ground for an open
^ Terminal 37 and ground = Battery If not check the wire to the main relay for an open. If the wire is OK, replace DME main relay.
^ Terminal 38 and ground = 0 Volts If not check the wire for a short to voltage. If wires are OK, refer to diagnosis of On-Board Computer or Antitheft System in BODY ELECTRICAL SAFETY AND ENTERTAINMENT.
^ Terminal 1 and ground = Battery If not check the wire for an open or short to ground, ignition coil, and wire between coil and ignition switch.
^ If all voltages are correct continue with step 5.
5. With the ignition OFF, connect a fused jumper from terminal 6 to terminal 2 of the fuel pump relay. Attempt to start the engine.
^ If the engine starts, replace the relay.
^ If the engine does not start, continue with step 6.
6. With the jumper from step 5 still in place, remove the cover from the fuel pump.
7. Disconnect the pump connector, turn the ignition switch to the run (ON) position and make the following voltage measurement at the pump connector (female half).
^ Green/violet wire terminal 2 and ground = Battery If not check the wire to the fuel pump relay for an open. If wire is OK, replace the fuel pump relay.
^ Green/violet and brown wire (terminal 2 and 1) = Battery If not check the wire to ground for an open
^ If all voltages are correct, remove the fused jumpers.
^ Check the function of the fuel pump, fuel lines and filter. Repair/replace as necessary.
^ If the fuel pump is OK, reconnect pump and continue step 8.
8. With the ignition switch OFF, disconnect the engine speed/reference sensor connector.
9. Turn the ignition switch to the run (ON) position and make the following voltage measurements at the engine speed/reference sensor connector (female half)
^ Terminal 1 and ground = Approx. 5 volts If not check wire to terminal 47 of the DME control unit connector for an open and short to voltage or ground
^ Terminal 1 and terminal 2 = Approx. 5 volts If not check wire to terminal 48 of the DME control unit connector for an open and short to voltage or ground
^ If voltages are correct measure resistance of engine speed/reference sensor. Resistance should be approximately 540 ohms. Repair or replace wires or sensor as necessary.
^ If sensor is OK, continue with step 10.
10. With the ignition switch OFF, disconnect the DME control unit harness connector. Make the following voltage measurements
DME Control Unit Harness Connector:
^ Terminal 8 and ground = 0 volts If not check wire to sensor for a short to voltage
^ Terminal 31 and ground = 0 volts If not check wire to sensor for a short to voltage
^ If all voltages are correct, check wires and sensor for continuity and shorts to ground. Resistance to ground should be greater than 500k ohms. Repair/replace cylinder identification sensor and/or wires as necessary.
11. If OK, replace the idle control valve and try to start the engine.
^ If the engine starts, retain the new idle control valve.
^ If the engine still does not start, the DME control unit may be defective.