Land Rover Bosch 5 2 1 Engine Management Systems Rover Manual

							BOSCH 5.2.1 ENGINE MANAGEMENT SYSTEM
Bosch 5.2.1 Engine Management System 137
BOSCH 5.2.1 ENGINE MANAGEMENT SYSTEM
Introduction
Bosch supplies the engine management system used on Discovery Series II and Range Rover 
beginning mid 1999 model year. It is referred to as the Bosch Motronic 5.2.1 system. The 
system supports  sequential fuel injection and waste spark ignition. The system is designed to 
optimize the performance and efficiency of the engine.
The key functions of the Bosch 5.2.1 engine management system are:
•  To control the amount of fuel supplied to each cylinder
•  To calculate and control the exact point of fuel injection 
•  To calculate and control the exact point of ignition on each cylinder
•  To optimize adjustment of the injection and ignition timings to deliver the maximum engine 
performance throughout all engine speed and load conditions
•  To calculate and maintain the desired air/fuel ratio, to ensure the 3 way catalysts operate at 
their maximum efficiency
•  To maintain full idle speed control of the engine
•  To ensure the vehicle adheres to the emission standards 
•  To ensure the vehicle meets with the fault handling requirements, as detailed in the ‘On-
board diagnostic II’ (OBDII) legislation
•  To provide an interface with other electrical systems on the vehicle
To deliver these key functions, the Bosch 5.2.1 engine management system relies upon a 
number of inputs and controls a number of outputs. As with all electronic control units, the ECM 
needs information regarding the current operating conditions of the engine and other related 
systems before it can make calculations, which determine the appropriate outputs. 
						

							BOSCH 5.2.1 ENGINE MANAGEMENT SYSTEM
138System Components
1. Mass Airflow & Temperature 
Sensor8. Idle Air Control Valve
2. Fuel Injectors 9. Ignition Coils
3. Spark Plugs/High Tension Leads 10. Engine Coolant Temperature 
Sensor
4. Fuel Pump Relay 11. Crankshaft Speed and Position 
Sensor
5. A/C Compressor Clutch & Cool-
ing Fan Relay12. Knock Sensor
6. Throttle Position Sensor 13. Camshaft Position Sensor
7. Heated Oxygen Sensor 
						

							BOSCH 5.2.1 ENGINE MANAGEMENT SYSTEM
Bosch 5.2.1 Engine Management System 139 System Inputs
The Bosch 5.2.1 system optimizes engine performance by interpreting signals from numerous 
vehicle sensors and other inputs. Some of these signals are produced by the actions of the 
driver, some are supplied by sensors located on and around the engine and some are supplied 
by other vehicle systems. 
The inputs are as follows:
•  Ignition switch (position II)
•  Throttle position sensor (TPS)
•  Crankshaft position sensor (CKP)
•  Camshaft position sensor (CMP)
•  Engine coolant temperature sensor (ECT)
•  Knock sensors (KS)
•  Air mass flow and temperature sensor (MAF)
•  Heated Oxygen sensors (HO2)
•  Immobilization signal
•  Fuel level signal
•  Vehicle speed sensor (VSS)
•  Rough road detection signal
•  Automatic temperature control (ATC) system request
•  Automatic gearbox information
•  Fuel tank pressure sensor 
Engine control module
The engine control module (ECM) is secured to a pressed steel bracket located at dash level on 
the right hand ‘A’ post. It features five separate electrical connectors. Each connector groups 
associated pin-outs together. 
The five connectors interlock when connected to the ECM. Therefore, they must be connected 
to the ECM in a specific order. Connector 1 must be used first, connector 2 second, connector 3 
third, and so on. The connectors can be disconnected only in the reverse order of this. It is not 
possible to remove the connectors from the ECM in any other order, the way in which the 
connectors interlock prevents this.
The main functions of the groups of pin outs incorporated into each connector are detailed in 
the following table.
Connector
numberConnector
colorMain functions
1  Black Main power supply and ground connections
2  Black Oxygen sensor inputs and Oxygen sensor 
3  Black All sensor inputs and outputs 
						

							BOSCH 5.2.1 ENGINE MANAGEMENT SYSTEM
140 The ECM is programmed during manufacture by writing the program and the engine ‘tune’ into 
the Flash EPROM (erasable programmable read only memory). This Flash EPROM can be 
reprogrammed in service, using TestBook. In certain circumstances, it is possible to alter the 
‘tune’ or functionality of the ECM using this process.
The engine management system (EMS) now used on Discovery Series II , is an  improvement 
over existing systems. The new EMS now improves the capability with respect to the 
monitoring, evaluating, diagnosing and correcting of many engine mechanical irregularities. It 
also has improved capability for monitoring and adapting its own operation to ensure that any 
mechanical variations do not affect the performance or the exhaust emissions of the engine.  
The ECM has advanced fault-handling capabilities. It can detect the type and severity of faults, 
store relevant engine operating conditions at the time a fault occurs and also store the time the 
fault occurred. The individual fault handling procedures the ECM completes will be explained 
throughout the section.  The ECM stores fault codes, referred to as ‘P’ codes. It is this ‘P’ code 
that Land Rover has to make available to third party scanning tools. The ‘P’ codes are defined 
within the OBDII legislation. Three environment variables are stored for each fault, in addition to 
Freeze Frame data.  Once recorded, details of a fault will stay in the ECM’s memory for 40 
‘trips’. 
A ‘trip’ is defined precisely by the on board diagnostic (OBD) legislation. It is a predetermined 
routine through which the engine or vehicle must pass before the ECM will attempt to  ‘validate’ 
a previously faulty signal. There are a number of OBD set routines. They are all grouped into 
one of several inspection/maintenance flags (IMF). These are:
•  Catalytic converter efficiency 
•  Purge (all markets) / evaporative emission leak detection diagnostic.
•  Oxygen sensor diagnostics
•  Oxygen sensor heater diagnostics
The above diagnostics all demand very strict engine conditions be met before they will run. By 
following the appropriate driving cycle, the IMF flags will indicate when the diagnostic 
completes. Most of the other diagnostics will operate within the first 30 seconds after engine 
starts.  Refer to the appropriate service literature for details on drive cycle, trip, and journey 
details for any given sensor/system.
TestBook can be used to view the diagnostic routines performed by the ECM, which need to be 
set before the relevant IMF becomes set. When a fault code is stored, it will indicate, via 
TestBook, the IMF required to ensure that successful repair can been verified. 
When certain fault conditions prevail, the EMS stores data relating to the value of certain engine 
inputs. These values, when stored, are known as ‘freeze frame data’. Freeze frame data is not 
the same as the three environmental variables stored when a fault is detected. Environmental 
variables are stored along with each fault (three variable conditions for each ‘P’ code), whereas 
freeze frame data is stored for the highest priority fault (different faults have different priorities, 
according to their likely impact on exhaust gas emissions). 
4  Black Most related vehicle system communications. 
5  Black Ignition coil control 
						

							BOSCH 5.2.1 ENGINE MANAGEMENT SYSTEM
Bosch 5.2.1 Engine Management System 141 Freeze frame data always records:
•  Engine speed 
•  Engine load 
•  ‘P’ code
•  Short term fuelling trim A / B
•  Long term fuelling trim A / B
•  Fuelling status A / B
•  Coolant temp
•  Road speed
The ECM will illuminate the malfunction indicator lamp (MIL) on detection of a fault, providing 
the fault has occurred on two consecutive driving cycles. This strategy ‘validates’ the fault, 
ensuring that the MIL does not illuminate needlessly. There is one exception to this, this being 
the ECM detecting that a catalyst-damaging misfire is currently occurring. In this case, the ECM 
will flash the MIL immediately the fault is detected. If the fault rectifies itself, the ECM will stop 
flashing the MIL, changing it to continuously ‘on’.
The MIL is illuminated by a bulb check facility when the ignition is switched to position II, a “MIL 
event fault”, or if the automatic gearbox requests it.
Ignition switch
The ignition switch supplies a signal to the ECM whenever it is turned to position II (‘ignition 
on’). Using this signal, the ECM is able to detect when the ignition switch is turned ‘on’ and 
when it is turned ‘off’. The ECM will initiate its ‘power-up’ sequence whenever the ignition is 
turned ‘on’. At this time it will energize the main relay (which, amongst other things, supplies the 
main feed to the ECM), energize the fuel pump relay and initiate a ‘self-check’ on the EMS 
system.
When it detects the ignition switch has been turned ‘off’, the ECM will stop the engine (if it was 
running) and record all the relevant information within its internal memory to enable the quick-
start functions to operate correctly. It will then initiate its ‘power-down’ sequence, which involves 
de-energizing the main relay.
Throttle position sensor
The throttle position sensor (TPS) is connected to the 
throttle valve shaft, located on the throttle body portion of 
the plenum chamber (see figure 50). It monitors the 
position and the rate of movement of the throttle valve, 
which is controlled by the driver via the throttle pedal and 
accelerator cable.  
						

							BOSCH 5.2.1 ENGINE MANAGEMENT SYSTEM
142 The throttle position sensor is a potentiometer. It receives a 5 volt supply from the ECM 
whenever the ignition switch is turned ‘on’. It then returns a proportion of the supplied voltage to 
the ECM to indicate its position and rate of movement. The actual position of the throttle valve, 
the direction in which it is moving (if it is moving) and, if so, the rate at which it is moving will 
determine the value of the voltage returned. The returned voltage will be in the range of 0.1 
volts (throttle fully closed) to 4.8 volts (throttle fully open). The ECM will supply 5 volts on the 
signal wire when the throttle potentiometer is disconnected. This voltage is used in the 
diagnostics of the wiring harness. The sensor has gold plated terminals to reduce the 
environmental impact. Care must be taken not to scratch the gold coating, particularly when 
using a multimeter connected directly to the sensor.
In addition to using the signal supplied by the throttle position sensor to determine the driver’s 
requirements, the ECM also uses the signal to check the plausibility of the signal supplied by 
the air flow meter. In circumstances where the signal supplied by the air flow meter indicates 
that only a small quantity of air is entering the engine, and the signal supplied by the throttle 
position sensor indicates a large throttle angle (i.e. throttle open), the ECM will store a ‘ratio 
fault’ indicating the throttle position and airflow have not matched.
The TPS sensor does not require any type of adjustment or calibration process. The Bosch 
5.2.1 ECM is able to ‘learn’ the closed throttle position using the signal it supplies. If the ECM 
detects a sensor failure, or the signal supplied by the throttle position sensor is deemed 
implausible, then it will introduce a substitute signal. The actual value of the substitute signal will 
be dependent upon a variety of signals received from other sensors located on and around the 
engine. Engine performance will be affected in these circumstances and the driver will notice 
the following:
•  The engine will idle poorly
•  The vehicle will default to 3rd / 4th gear (limp home strategy automatic vehicles only)
•  The engine will run poorly and respond poorly to throttle pedal movement
•  The gearbox will not kickdown (automatic vehicles only)
•  Altitude adaptations will be incorrect (engine performance affected even more when the 
vehicle is operated at high altitudes
Expected Values
TestBook will retrieve the fault code and perform the necessary diagnostics. The sensor can 
also be probed directly, providing the care point mentioned above is adhered to. TestBook also 
has the capability of displaying the value of the TPS signal received by the ECM. It displays this 
on the ‘live reading’ screen. It will also display the altitude adaptive value currently being used 
on this screen.
Throttle
AngleMax/Min
ValueNominal
ValueDiagnostic
Fault ValueNominal
Resistance
Closed 0.811 mV 0.894 mV 0.960 mV 1.013kW
Fully
Open0.162 mV 0.096 mV 0.040 mV 2.575kW 
						

							BOSCH 5.2.1 ENGINE MANAGEMENT SYSTEM
Bosch 5.2.1 Engine Management System 143 Crankshaft position sensor
The crankshaft position sensor is located in the engine 
block, just below number 7 cylinder (see figure 51). It 
protrudes through the cylinder block and is positioned 
adjacent to the face of the flywheel or flex plate. The 
sensor reacts to a ‘drilled reluctor’ incorporated into the 
flex plate to ascertain engine speed and position 
information. The sensor is located on a spacer and is 
secured in position by a single bolt. The spacer is 18 mm 
(0.709 in) thick on vehicles used with automatic 
transmission. The thickness of the spacer determines 
how far the sensor protrudes through the cylinder block 
and, therefore, sets the position of the sensor in relation 
to the flywheel or flex plate. The sensor and the spacer 
are covered by a protective heat shield. The sensor has 
three wires attached to it; one signal wire, one ground wire connected to the ECM and one 
ground wire connected to vehicle ground. This last wire acts as a shield to earth any stray 
electromagnetic radiation produced from the crankshaft signal. 
						

							BOSCH 5.2.1 ENGINE MANAGEMENT SYSTEM
144 The crankshaft sensor is an inductive type sensor which produces a sinusoidal output voltage 
signal. The following illustration shows a typical crankshaft signal over a 480° crankshaft 
revolution. This voltage is induced by the proximity of the moving toothed reluctor, which excites 
the magnetic flux around the tip of the sensor when each tooth passes. This output voltage will 
increase in magnitude and frequency as the engine rpm rises and the speed at which the 
reluctor passes the sensor increases. The signal voltage will peak at approximately 6.5 volts if 
connected to the ECM (further increases in engine speed will not result in greater magnitude). 
The ECM neither specifically monitors nor reacts to the output voltage (unless it is very small or 
very large) but does measure the time intervals between each pulse (i.e. signal frequency). The 
signal is determined by the number of teeth passing the sensor, and the speed at which they 
pass. The teeth are spaced at 6° intervals, with two teeth missing at 60° BTDC to give the ECM 
a hardware point of reference, so there is a total of 58 teeth.
The ECM outputs an engine speed signal to the automatic gearbox, the SLABS ECU, the 
instrument pack and the ACE ECU. The signal to the automatic gearbox TCM and the SLABS 
ECU are supplied via the CAN link, while the signals to the ACE ECU and the instrument pack 
are carried via a frequency dependent digital signal.
The signal produced by the crankshaft position sensor is critical to engine running. There is no 
backup strategy for this sensor and failure of the signal will result in the engine stalling and/or 
failing to start. If the sensor fails when the engine is running, then the engine will stall, a fault 
code will be stored and details captured, of the battery voltage, coolant temperature and air 
temperature at the time of the failure. If the signal fails when the engine is cranking, then the 
engine will not start and no fault will be stored, as the ECM will not detect that an attempt had 
been made to start the engine. In both cases the tachometer will also cease to function 
immediately and the MIL lamp will not extinguish.
During the power-down procedure, which occurs when the ignition is switched ‘off’, the ECM 
stores details of the position of the crankshaft. This enables the ECM to operate the injectors 
appropriately to aid quick engine start, which serves to reduce emissions when the engine is 
cold. 
						

							BOSCH 5.2.1 ENGINE MANAGEMENT SYSTEM
Bosch 5.2.1 Engine Management System 145 Camshaft position sensor
The camshaft position sensor is located in the timing cover and the tip of the sensor is 
positioned in close proximity to the camshaft gear. The camshaft gear incorporates four teeth. 
The camshaft position sensor is a hall-effect sensor which switches a battery fed supply ‘on’ 
and ‘off’. The supply is switched when the teeth machined onto the camshaft gear pass by the 
tip of the sensor. The four teeth are of differing shapes, so the ECM can determine the exact 
position of the camshaft at any time. Using this signal in conjunction with the signal supplied by 
the crankshaft position sensor, the ECM is able to detect the firing position of the engine (i.e. the 
exact position and stroke of each piston). Care must be taken  to avoid fitting an incorrect 
camshaft gear, as the gear used on engines equipped with GEMS EMS looks similar, but if this 
gear is used in place of the correct gear, a fault will be stored, as the two gears have a different 
tooth spacing pattern.
Unlike an inductive type sensor, a hall-effect sensor does not produce a sinusoidal output 
voltage (sine wave).
Camshaft/Crankshaft Signal Output 
Instead it produces a ‘square wave’ output. The edges are very ‘crisp’, rising very sharply and 
falling very sharply, giving the ECM a defined edge on which to base its calculations. An 
implausible signal will result in the following:
•  The MIL lamp illuminated after ‘validating’ the fault)
•  Loss of performance, due to the corrective ignition strategy being disabled. A default igni-
tion map is used which retards the timing to a safe position
•  Injector operation possibly 360° out of phase, i.e. fuel injected during compression stroke 
rather than during exhaust stroke
•  Quick crank/cam synchronization on start-up feature disabled
•  Some Oxygen sensor diagnostics disabled 
						

							BOSCH 5.2.1 ENGINE MANAGEMENT SYSTEM
146 In addition, the ECM will store a relevant fault code and capture the input signal supplied by the 
engine coolant temperature sensor, and the engine load calculation and the engine rpm at the 
time of failure. TestBook will display the live readings from the camshaft sensor.    
Engine coolant temperature sensor
The engine coolant temperature sensor is located near the 
top of the engine, adjacent to the coolant outlet pipe. The 
sensor features four electrical connections; two are used on 
Discovery Series II  applications and all four are used in 1999 
MY Range Rover applications. The sensor conforms to the 
conventional negative temperature coefficient (NTC) electrical 
characteristics.
The signal supplied by the engine coolant temperature sensor 
is critical to many fuel and ignition control strategies. 
Therefore, the Bosch 5.2.1 system incorporates a complex 
engine coolant temperature sensor default strategy, which it implements in the event of failure. 
The ECM uses several alternative inputs to determine the specific default value selected in 
these circumstances. The amount of time the engine has been running and the temperature of 
the air entering the engine are the primary inputs used to determine the default value. The 
software model of the temperature increasing will finish when it reaches a value of 150°F 
(65°C). This value is then used until the engine is switched off.
The following symptoms may be noticeable in the event of an engine coolant temperature 
sensor failure:
•  The MIL lamp illuminated (after ‘validating’ the fault)
•  Poor engine hot and cold start
•  Overheat warning lamp (incorporated within the Instrument pack) is illuminated 
•  Excessively hot or cold needle reading on the temperature gauge