1998 BMW 540i Ac system

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OBD-3
On-Board
~iactnosticsl
Additional MIL information:
A fault code is stored within the ECM upon the first
occurrence of a fault in the system being checlted.
Two complete consecutive drive cycles with the iault
present illuminate the MIL. The exception to the two-fault
requirement is a catalyst-damaging fault, which illuminates
the MIL immediately.
If the second drive cycle was not complete and the fault
was not checked, the ECM counts the third drive cycle as
the next consecutive drive cycle. The MIL illuminates
if the
system is checked and the fault is still present.
Once the MIL is illuminated, it remains illuminated until the
vehicle completes three consecutive drive cycles without
detecting a fault.
0 An existing fault code is cleared from memory
automatically when the vehicle completes
40 consecutive
drive cycles without the fault being detected.
In order to automatically clear a catalyst-damaging fault from
memory, the condition underwhich the fault occurred must be
evaluated for 80 consecutive drive cycles without the fault
reoccurring.
A generic scan tool connected to the BMW data link
connector (DLC) or OBD
I1 plug can display diagnostic trouble
codes (DTCs), along with the conditions associated with the
illumination of the MIL. Using a more advanced or
BMW-
dedicated scan tool, additional proprietary information is
normally available.
Scan tool and scan tool display
The complexity of the OBD I1 system requires that all
diagnostics begin by connecting a scan tool to the vehicle.
Aftermarltet scan tools can be connected to either the 16-pin
OBD
I1 plug or the 20-pin BMW DLC in the engine
compartment
(ii installed). Data from the OBD II plug may be
limited, depending on scan tool and vehicle.
OBD
I1 standards reouire that the 16-oin OBD I1 oluo be
located within three
(3) feet of the driier and not're&ire any
tools to access.
Starting with June 2000 production, the 20-pin BMW DLC,
previously located in the engine compartment, was
discontinued. Diagnostic, coding and programming functions
are incorporated into the OBD
II plug, located under left side
of dashboard.
On cars built up to 06
/ 2000: when accessing emissions
related DTCs through the 16-pin OBD
I1 plug, malte sure the
BMW 20-oin DLC
caD is installed.

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- -
On-Board Diagnostics
Professional diagnostic scan tools available atthe time of this
printing include the BMW factory tools
(DISplus, GTI,
MoDiC) and a small number of aftermarket BMW-specific
tools. See
020 Maintenance.
In addition to the professional line of scan tools, inexpensive
generic OBD
II scan tool software programs and handheld
units are readily available. Though limited, they are
nonetheless powerful diagnostic tools. These tools read live
data streams and freeze frame data as well as a host of other
valuable diagnostic data.
Diagnostic monitors
Diagnostic monitors run tests and checks on specific
emission control systems, components, and functions.
A complete drive cycle is requiredforthe tests to bevalid. See
Drive cycle in this repair group. The diagnostic monitor
signals the
ECM of the loss or impairment of the signal or
component and determines if a signal or sensor is faulty
based on
3 conditions:
* Signal or component shorted to ground
Signal or component shorted to
B+
Signal or component missing (open circuit)
The OBD
II system monitors all emission control systems that
are installed. Emission control systems vary by vehicle model
and year. For example, a vehicle may not be equipped with
secondary air injection, so no secondary air readiness code
would be present.
OBD
II software monitors the following:
Oxygen sensors
Catalysts
Engine misfire
- Fuel tank evaporative control system
Secondary air injection Fuel system
Oxygen sensor monitoring. When driving conditions allow,
response rate and switching time of each oxygen sensor is
monitored. The oxygen sensor heater function is also
monitored. The OBD
II system differentiates between
precataylst and post-catalyst oxygen sensors and reads each
one individually. In order
forthe oxygen sensor to be
effectively monitored, the system must be in closed loop
operation.

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On-Board Diagnostics
Catalyst monitoring. Thisstrategy monitors the outputofthe
precatalyst and post-catalyst oxygen sensors, comparing the
oxygen content going into the catalytic converter to the
oxygen leaving the converter.
The diagnostic executive
lknows that most of the oxygen
should be used up during the oxidation phase. If it detects
higherthan programmed values, afault is set and the MIL
illuminates.
Misfire detection. This strategy monitors crankshaft speed
fluctuations and determines if an enoine misfire occurs bv
monitoring variations in speed between each crankshaft
sensortrigger point. This strategy is so finely tuned that it can
determine the severity of the misfire.
The system determines
if a misfire is occurring, as well as
other pertinent misfire
information such as:
Specific
cylinder(s)
Severity of the misfire event
Emissions relevant or catalyst damaging
Misfire detection is an on-going monitoring process that is
only disabled under certain limited conditions.
Secondary air injection monitoring. Secondary air
injection is used to reduce HC and CO emissions during
engine warm up. Immediately following a cold engine start
(-1 0" to 40°C), fresh air (and therefore oxygen) is pumped
directly into the exhaust
manifold. By injecting additional
oxygen into the exhaust manifold, catalyst warm-up time is
reduced.
Secondary air system components are:
Electric air injection pump
* Electric pump relay
* Non-return valve
Vacuum
I vent valve
- Stainless steel air injection pipes
Vacuum reservoir
The secondary air system is monitored via the use
of the pre-
catalyst oxygen sensors. Once the air pump is active and air
is injected into the system, the signal at the oxygen sensor
reflects a lean condition. If the oxygen sensor signal does not
change, a fault is set and the faulty
bank(s) identified. If after
completing the next cold startafault is again present, the MIL
illuminates.

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OBD-6
On-Board Diagnostics
Fuel system monitoring. This monitor looks at the fuel
delivery needed (long
/short term fuel trim) for proper engine
operation based on programmed data. If too much or not
enough fuel is delivered over a predetermined time, a DTC is
set and the MIL illuminates.
Fuel trim refers to adiustments to base fuel schedule.
Lono- ., term fuel trim refers to gradual adjustments to the fuel
calibration adjustment as compared to short term fuel trim.
Long term fuel trim adjustments compensate for gradual
changes that occur over time.
Fuel system monitoring monitors the calculated injection time
(ti) in relation to enginespeed, load and precatalyticconverter
oxygen
sensor(s) signals.
Using this data, the system optimizes fuel delivery for all
engine operating conditions.
Evaporative system monitoring. This monitor checks the
the fuel storage system and related fuel lines for leaks. It can
detect very small leaks anywhere in the system.
A leak detection unit (LDP or DMTL) is used to pressurize the
evaporative control system on a continuous basis (as the
drive cycle allows) and to
check system integrity.
Drive cycle
The OED II drive cycle is an important concept in
understanding OBD
II requirements. The purpose of the drive
cycle is to run ail of the emission-related on-board diagnostics
over a broad range of driving conditions.
A drive cycle is considered complete when all of the
diagnostic monitors have run their tests without interruption.
~ora drive cycle to be initiated, the vehicle must be started
cold and brought up to
1 60°F and at least 40°F above its
original starting temperature.
Readiness codes
Inspection/maintenance (I/M) readiness codes are mandated
as part of OBD
II. The readiness code is stored aftercomplete
diagnostic monitoring of specified components and systems
is carried out. The readiness code function was designed to
prevent manipulating an
I/M emission test procedure by
clearing faults codes or disconnecting the ECM or battery.

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On-Board Diagnostics
Readiness codes indicate whether the OED Ii system is
actually ready to monitor the various emission control
systems on the vehicle. The vehicle must complete a drive
cycle to set readiness codes. The code is binary:
0 for ready
1 for not ready
f
4 The parameters which are monitored for readiness are:
llM readiness codes
1. Catalyst efficiency
2. Catalyst heating
3. Fuel tank evaporative control
4. Secondary air injection
5.
NC refrigerant
6. Oxygen sensors
7. Oxygen sensor heaters
8. Exhaust gas recirculation
Readiness codes are set to 1 (not ready) in the following
cases:
~9~~.f~[<+t~t~p:,~;:#j~~{]~y~ ,,... , , 8701Dbd001
The battery or ECM is disconnected.
When
all zeros are displayed, the system has established
DTCs are erased after completion of repairs and a drive
cycle is not completed.
readiness. Readiness codes
can be displayed using BMW
and aftermarket scan tools.
An
OED II scan tool can be used to determine IIM readiness.
Diagnostic trouble codes (DTCs)
SAE standard J2012 mandates a 5-digit diagnostic trouble
code (DTC) standard. Each digit represents a specific value.
Emission related DTCs
start with the letter P for power train.
When the engine service
light (MIL) is illuminated it indicates
that a DTC has been stored.
DTCs are stored as soon as they occur, whether or not the
engine service light illuminates.
DTCs store and display a time stamp.
DTCs record the current fault status: Present, not currently
present, or intermittent.

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OBD-8
I On-Board Diagnostics
DTC digit interpretation
1st digit
P powertrain
B body
C chassis
2nd digit
0 SAE
1 BMW
3rd digit
0
1
2
3
4
5
6
7
4th - 5th digits total
system
airlfuei induction
fuel injection
ignition system or misfire
auxiliary emission control
vehicle speed
& idle control
ECM
inputs/outputs
transmission
individual circuits or
components
DTC example: P 0 3 0 6
P: A powertrain problem
0: SAE sanctioned or 'generic'
a 3: Related to an ignition system / misfire
06 Misfire detected at cylinder #6
DTCs provide a freeze frame or snap-shot of a vehicle
performance or emissions fault at the moment that the fault
first occurs. This information is accessible through generic
OED I1 scan tools.
Freeze frame data contains, but is not limited to, the following
information:
Engine load (calculated)
Engine rpm
Short and
long term fuel trim
Vehicle speed
Coolant temperature Intake manifold pressure
Open/closed loop operation
Fuel pressure (if available)
DTC

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On-Board Diagnostics
DIAGNOSTIC TROUBLE CODES
(DTCs)
Below is a listing of E39 powertrain (automatic transmission
and engine)
SAE P-codes, the corresponding BMW fault
codes, and the fault code definitions.
BMW fault codes expand on the SAE sanctioned DTCs and
are accessible primarily through the BMW diagnostic scan
tool or a BMW-specific scan tool.
l~utomatic transmission diagnostic trouble codes
P-code
IBMW-FC I DTC Definition
Ip0560 196 ISystem Voltage I
IPO~OO I129 l~eriai Communication Link I
1~0715 116 I InpuVTurbine Speed Sensor 'A' Circuit I
PO600
PO601
PO603
PO606
PO705
PO705
PO709
144
80
81
82
8
60
60
PO71 5
PO71 6
PO717
PO720
PO720
PO720
I I
PO721 159 loutput Speed Sensor Circuit RangeIPerformance I
Serial Communication Link
Internal Control Module Memory Check Sum Error
Internal Control Module Keep Alive Memory (KAM) Error
ECMIPCM Processor
Transmission Range Sensor 'A' Circuit Maliunction (PRNDL Input)
Transmission Range Sensor
'A' Circuit Malfunction (PRNDL input)
Transmission Range Sensor
'A' Circuit Intermittent
I I'
1~0722 132 IOutput Speed Sensor Circuit No Signal I
33
33
33
32
42
59
PO720
I I
PO727 1150 I Engine Speed Input Circuit No Signal
InpuVTurbine Speed Sensor 'A' Circuit
inpuVTurbine Speed Sensor 'A' Circuit RangeiPerformance
InpuVTurbine Speed Sensor 'A' Circuit No Signal
Output Speed Sensor Circuit
Output Speed Sensor Circuit
Out~ut Speed Sensor Circuit
PO720 1106 /output Speed Sensor Circuit
62
Output Speed Sensor Circuit
PO730
PO730
PO731
PO731
PO731 I I
100
102
50
51
100
PO731
incorrect Gear Ratio
Incorrect Gear Ratio
Gear 1 incorrect Ratio
Gear 1 incorrect Ratio
Gear 1 Incorrect Ratio
PO732 152 /Gear 2 Incorrect Ratio
131
Gear
1 Incorrect Ratio

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OBD-12
On-Board Diagnostics
Automatic transmission diagnostic trouble codes (continued)
P-code
PI747
PI747
PI 747
PI748
PI748 I I
PI748
PI748
PI748
PI 748
PI 749
PI 750
P1750
PI761
PI761
BMW-FC
150
151
156
15
80
-- PI762
PI763
PI764
PI765
PI765
PI765
P1770
DTC Definition
CAN-BUS Monitoring
CAN-Bus Monitoring
CAN-Bus Monitoring
Transmission Control Module Self-Test
Transmission
Control Module Self-Test
PI748 182 l~ransmission Control Module Self-Test
81
103
105
110
I I
Transmission Control Module Self-Test
Transmission Control Module Self-Test
Transmission Control Module Self-Test
Transmission Control Module Self-Test
19
19
19
147
154
158
146
PI 790
PI791
P1792
PI 794
PI 801
P1802
PI 803
PI 831 Shiftiock Solenoid High input
Shiftlock Solenoid
Low Input
Shiftlock Solenoid Open Circuit
CAN Throttle Valve
CAN Throttle Valve
CAN Throttle Valve
CAN
Torpue Interlace
CAN Torque Reduction
PI 780
I I -
108
54
96
2 19
PI 780 1163 ICAN Torque Reduction
152
80
81
82
80
16
17 18
1 Secondary Pressure Solenoid Communication Error
(M52: Internal
Transmission Control Module Memory Error)
Secondary Pressure Solenoid Circuit
Rangelperformance (System Voltage Input Low)
Secondary Pressure Solenoid Circuit
RangeIPerformance (System Voltage Input Low)
Shiftioclc Solenoid
Shiftiocic Solenoid
internal Transmission Control Module Memory ChecksumlEPROM Error
internal Transmission Control Module Memory
ChecksumIEEPROM Error
internal Transmission Control Module Watchdog Error
internal Transmission Control Module Memory Checksum Error
Shift Solenoid
'A' Low Input
Shift Solenoid
'8' Low Input
Shift Solenoid
'C' Low input
Pressure Control Solenoid
'A' Circuit High
Pressure Control Solenoid 'B' Circuit High
PI832
PI833 13 IPressure Control Solenoid 'C' Circuit High
2