1999 BMW 540i electrical

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Fuel Tank and Fuel Pump
Warnings and cautions
Observe the following warnings and cautions when servicing
the fuel system.
WARNING-
* The fuel system is designed to retain pressure even when
the ignition is off. When working with the fuelsystem, loos-
en the fuel lines slowly to allow residual
fuel pressure to
dissipate. Avoid spraying fuel. Use shop rags to capture
leaking fuel.
Before beginning any work on the fuel system, place a
fire extinguisher in the vicinity of the work area.
Fuel is highly flammable. When working around fuel, do
not disconnect any wires that could cause electrical
sparks. Do not smoke or worknearheaters or other fire
hazards.
* Always unscrew the fuel tank cap to release pressure
in the
tanlc before working on the tank or lines.
When disconnecting a fuel hose, wrap shop rag around
end of hose to prevent spray of fuel under pressure.
Do not use a work light with an incandescent bulb near
any fuel. Fuel may spray on the hot bulb causing a fire.
0 Make sure the worlc area is properly ventilated.
CAUTION-
- Prior to disconnecting the battery, read the battery discon-
nection cautions given in
001 General Cautions an4
Warnings.
Before
making any electrical tests with the ignition
turned on, disable the ignition system as described in
120 Ignition System. Be sure the battery is discon-
nected when replacing components.
To prevent damage to the ignition system or other DME
components, including the engine control module
(ECM), always connect and disconnect wires and test
equipment with the ignition off.
Cleanliness is essential when
worl~ing with the fuel sys-
tem. Thoroughly clean the fuel line unions before dis-
connecting any of the lines.
Use only clean tools. Keep removed parts clean and
sealed or covered with a clean, lint-free cloth, especial-
ly if completion of the repair is delayed.
Do not move the car while the fuel system is open.
Avoid using high pressure compressed air to blow out
lines and components. High pressure can rupture inter-
nal seals and gaskets.
Always replace seals, O-rings and hose clamps.

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.-- -
/ Fuel Tank and Fuel Pump - .. -. -- 1
Fuel pump fuse and relay
Troubleshooting of any fuel pump fault should begin with
checking the fuel pump fuse and the fuel pump relay. The
DME main relay should also be checked. The fuel pump relay
is located behind right side luggage compartment interior
panel.
I Fuel pump relay
BLU =blue ERN = blo$,m GRN =groan GRY = grsy ORG =orange PNI< =pink RED =red VIO =violel WHT = wlilte
rk-; I I 1 ECM
I I I 31 8 ,._--___.I
NOTE-
Special tools are required for some of the tests described
here.
4 Fuel pump circu~t is fuse-protected.
0 6-cylinder models with Siemens DME MS41 .I, MS42, V-8
models with Bosch DME M5.2, M5.2.1 englne manage-
ment: Fuse
F54,15A (luggage compartment fuse panel)
6-cylinder models with Siemens DME MS43 engine man-
agement: Fuse
F22,25A (glove compartment fuse panel)
V-8 models with Bosch DME M7.2: Fuse F54,25A (lug-
gage compartment fuse panel)
- Fuse 31 in glove compartment fuse panel supplies power to
coil side of fuel pump relay. Engine control module (ECM)
supplies switched ground to relay. During starting, fuel pump
runs as long as ignition switch is in START position and con-
tinues to run once engine starts. If electrical system fault in-
terrupts power to fuel pump, engine will not run.
. .
Operating fuel pump for tests
- To operate fuel pump for testing purposes without having to
run engine, bypass fuel pump relay to power pump directly.
< To run fuel pump, open luggage compartment and release
right side trim panel.

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- Fuel Tank and Fuel pump]
Remove fuel pump
relay (arrow).
4 Connect relay socitet terminal 6 (redlviolet wire) to relay
socket terminal
2 (whitelblue wire) with a fused jumper wire.
After completing tests, remove jumper harness.
CA
UTIOG
Relay locations may vary Use care when identifying relays
and making electrical checks at
the fuse/relay panel. See
610 Electrical Component Locations for additional re-
lay information.
The fuel pump relay has a 1.5
md red/violet wire at
terminal
6 in the relay socket. Terminal2 has a 2.5md
white/blue wire. See ELE Electrical Wiring Diagrams
for additional wiring information.
NOTE-
* The fuel pump will run as soon as the jumper wire Is at-
tached.
The jumper wire should be 1.5
md (14 ga.) and include
an in-line fuse holder with a 15A fuse. To avoid
fuse/relay
panel damage from repeated connecting and disconnect-
ing, also include a toggle switch in the jumper harness.
- If pump does not run with jumper installed, fault could be in
fuel pump, fuses
F31 or F22 1 F54, or wiring to pump. Check
pump, fuses and its wiring as described below.
Fuel pump electrical circuit, testing
- The test given below assumes that the fuel pump relay circuit
is functioning correctly as described earlier. Access to the
pump is from below the rear seat bottom cushion.
- Remove rear seat lower cushion by lifting front edge off left
and right catches.

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.- -
Fuel Tank and Fuel purnpl
Fuel pump power consumption, testing
To achieve accurate test results, the battery voltage at the
fuel pump connector should be
12.6 volts. Charge the battery
as necessary.
A higher than normal power consumption may indicate a
worn fuel pump, which may cause intermittent fuel starvation
due to pump overheating and seizure. The only remedy is
pump replacement.
A lower than normal power consumption
may indicate a blockage. Be sure to check that the return line
and the pump pickup are not obstructed before replacing the
pump.
- Expose right side access cover:
Peel forward lip of carpet.
Release rubber grommet from center of access cover insu-
lation.
Peel back insulation at perforations to expose fuel tank ac-
cess cover.
Remove right side cover to expose electrical harness con-
nector.
Disconnect harness connector from tank sending unit by slid-
ing lock back. Lift off connector.
Test fuel pump for current draw by attaching digital ammeter
between pump and harness (terminal
2, whitelblue wire) and
connect a jumper wire between pump and harness (terminal
1, brown wire) as shown.
CAUTION-
Do not allow the test leads to short to ground.
NOTE-
See 600 Electrical Systern-General for information on elec-
trical tests
using a digital multirneter.
Run pump as described in Operating fuel pump for tests.
- Compare ammeter reading with specification listed in ac-
companying table.
Fuel
pump current
Current consumption (average) 9.5 amps

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.-
I Fuel Tank and Fuel Pump
- Expose right side access cover:
Peel forward lip of carpet.
Release rubber grommet from center of access cover insu-
lation.
Peel back insulation at
perforations to expose fuel tank ac-
cess cover.
Remove right side cover to expose electrical harness con-
nector.
WARNING -
Fuel may be spilled. Do not smolce or work near heaters or
other fire hazards.
When disconnecting fuel hose, wrap shop rag around
end of hose to prevent spray of fuel under pressure.
Remove
tank sending unit:
Release electrical harness by sliding lock back, then lifting
off connector.
a Disconnect hose (arrow).
Unscrew threaded collar from fuel
pumpifuel level sender.
NOTE-
BMW special spanner 16 1 020 should be used to remove
and install the threaded collar. Damage to the collar may re-
sult if the special tool is not used.
Slowly withdraw assembly from tank, allowing fuel to drain
off. If necessary, push level sender arm toward sending
unit to facilitate removal.
CAUTION-
Do not bend fuel level sender arm.
To remove fuel pump, press locking tabs (arrows) towards
pump body.
Lifl out pump, using care not to damage hoses.

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.- .
Fuel Tank and Fuel Pump
- To reinstall:
Use new sealing ring at tank collar.
* Align tab of sending unit with matching recess in opening
of tank.
Be sure that fuel line connections point in same direction
as they came out.
Reconnect harness connector and hose.
Fill tank and check for leaks by running engine.
Install access cover and its mounting fasteners.
CAUTIOI\C
After finishing repairs but before starting engine, be sure
there is at least
5 liters (1.5 gallons) of fuel in the tank. The
NOTE-
It is common practice to replace the fuel filter when the fuel
pump
unit is replaced. See 020 Maintenance.
Tightening torque
Tank collar locking ring to tank 35 Nm (26 lb-ft)
Fuel level sender (left side),
removing and installing
The procedure for removing and replacing the left side fuel
level sender is
simllar to that used for the r~ght side. There is
no fuel pump on the left side.
- Remove rear seat lower cushion by lifting off catches at front.
- Expose left side access cover:
- Peel forward lip of carpet.
Release rubber grommet from center of access cover
insulation.
Peel back insulation at
perforations to expose fuel tank
access cover.
Remove cover to expose electrical harness connector.
WARNING-
Fuel may be spilled. Do not smoke or work near heaters or
other fire hazards.
When disconnecting fuel hose, wrap shop rag around
end of hose to prevent spray of fuel under pressure.

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/ ~uel Tank and Fuel Pump
4 Remove tank sending unit:
Disconnect electrical harness connector.
Disconnect hose (arrow).
- Unscrew threaded collar from fuel level sender.
NOTE-
BMW special spanner 16 1 020 should be used to remove
and install the threaded collar. Damage to the collar may
result if the special tool is not used.
Slowly withdraw assembly from tank, allowing fuel to drain
off. If necessary, push level sender arm toward sending
unit to facilitate removal.
CA UTIOW-
Do not bend fuel level sender arm.
4 Once level sensor unit has been lifted partially out of tank,
disconnect tank siphon hose by pressing tabs (arrows).
- Installation is reverse of removal
Attach tank siphon hose to sender unit firmly.
Use new sealing ring at tank collar.
. Be sure that fuel sender float points in same direction as
during removal.
- Reconnect harness connector.
Fill tank and
check for leaks by running engine.
CAUTION-
After finishing repairs but before starting engine, be sure
there is at least
5 liters (1.5gallons) of fuel in tan/(. The fuel
pump will be damaged if run without fuel.
Tightening
torque
Tank collar loclting rlng to tanlt 35 Nm (26 lb-ft) -

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Fuel Tank and Fuel pump/
- Remove suction hose from tank filler neck carefully to avoid
damaging filler neck baffle plate.
CAUTION-
After finishing repairs but before starling engine, be sure
there is at least
5 liters (1.5 gallons) of fuel in tanlc. The fuel
pump will be damaged if run without fuel.
Fuel tank, removing and installing
- Remove fuel tank filler cap and drain tank as described
earlier.
- Disconnect negative cable from battery.
CAUTION-
Prior to disconnecting the battea read the battery discon-
nection cautions given in
001 General Cautions and
Warnings.
- Remove rear seat bottom cushion. Peel forward lip of carpet
from beneath seat cushion and carefully peel back insulation
to expose fuel tank access cover on left and right sides. Re-
move covers.
Disconnect right side supply hose and
electr~cal harness
connector (arrows).
D~sconnect left side return hose and electrical harness
connector.
Working inside car, disconnect parking
bralte cable ends
from parking brake lever. See
340 Brakes.
Lift car and support safely.
Make sure the car is stable and
we/ supported at all times.
Use a professional automotive lift
orjack stands designed for
the purpose. A floorjaclc is not adequate support.
- Remove complete exhaust system and heat shield. See 180
Exhaust System.
- Remove drive shaft. See 260 Driveshaft