On-board diagnostics system — operating principle and fault codes (BMW 5 Series E28)

Information about diagnostic devices

The proper functioning of injection system components and exhaust gas toxicity reduction is checked using a universal digital meter (multimeter) (see illustration below). Using a digital meter is preferable for several reasons. Firstly, it is quite difficult to measure the value of an analog meter (sometimes it's impossible), determine the result of the reading with an accuracy of up to hundredths and thousandths, while when examining circuits that include electronic components, such accuracy becomes especially important. The second, no less important, reason is the fact that the internal circuit of the digital multimeter has a fairly high impedance (the internal resistance of the device is 10 mOhm). Since the voltmeter is connected to the circuit being tested in parallel, the accuracy of the measurement is higher, the smaller the current that passes through the device itself. This factor is not significant when measuring relatively high voltage values (9÷12 V), but it becomes decisive when diagnosing elements that produce low-voltage signals, such as, for example, a lambda probe, where we are talking about measuring fractions of a volt.

Parallel monitoring of signal parameters, resistances and voltages in all control circuits is possible using splitter, connected in series to the engine control unit connector. In this case, with the engine turned off, running, or while the car is moving, the parameters of the signals at the terminals of the splitter are measured, from which a conclusion is made about possible defects.





The use of a high-impedance digital multimeter in diagnostics of the systems under consideration significantly increases the accuracy of the measurements taken

For diagnostics of electronic systems of the engine, automatic transmission, ABS, SRS special diagnostic scanners or BMW testers can be used DIS, MoDIC (programmable from PC). In addition, scanners and specialized diagnostic analyzers can be used for this purpose, for example CS 1000, Bosch FSA 560, KTS 300 (HAMMER), Sun 2013, or a regular personal computer with a special adapter, cable and installed OBD browser program (for example, the Bosch ESI [tronic] program in Russian, the Car Scanner program.

Universal KL-line adapter, serves to match signals of the RS-232 port and ISO-9141 (K-line) and ALDL interfaces. Various cables required for diagnostics of a specific car brand can be connected to the adapter connectors. Switches and indicator elements installed in the adapter allow you to select the necessary operating modes and roughly evaluate the operation of the output lines. Thus, the glow of the green LED marked L-line indicates the connection of the L line to the car body. The glow of the red LED marked K-line indicates the high potential that is present at this moment on the K line. When the connection with the car is established, the blinking of the indicators may be imperceptible to the eye due to the high exchange rate. Connection to the computer is made directly to the 25-pin COM port or using the "RS-232 Cable 25 pin - 9 pin" to the 9-pin COM port.



Some scanners, in addition to the usual diagnostic operations, allow, when connected to a personal computer, to print out the basic diagrams of electrical equipment stored in the memory of the control unit (if pledged), program the anti-theft system, monitor signals in the car circuits in real time.



To diagnose electronic control systems of a car, hand-held scanners MoDIC, KTS 300 (Bosch) or a personal computer can be used.

Adapter for matching K and L diagnostic lines with PC COM port

Reading of fault codes recorded in the memory of the self-diagnostic system on some models can also be done using the "check engine" indicator on the dashboard.

Connecting a PC for Car Diagnostics

For diagnostics, devices from ToolRama, Inc. can also be used, for example. (3500 NW Boca Raton Blvd., Boca Raton, Florida, 33431, USA 1 877 866 5726 - 561 750 4511 - 561 338 8447 FAX) with cartridges for a specific car model.



All tester cartridges can be used in the scanner as well. In this case, the functions will be limited to reading and clearing memory only.

• r000 tester with T051A (B or C) cartridge or P000 scanner with T041 cartridge,
• universal cable N000,
• connector N001.

The scanner only reads the fault memory and clears the fault memory. The tester can additionally activate and display current data.

The OBD II cartridge performs the following functions:

• Read and clear OBD II trouble codes. Display oxygen sensor test results.
• Continuous monitoring of ignition systems, injection systems and components.
• Displays a list of current data and recorded intermittent failures:
• Absolute pressure in the intake manifold;
• Oxygen sensor voltage;
• Engine coolant temperature;
• Estimated engine load;
• Car speed;
• Fuel quality;
• Air flow (by mass);
• Ignition timing;
• Throttle position;
• Intake air temperature.

You can find more information about the devices on the websites programatools.com, bosch.de.

General description of the OBD self-diagnosis system

The OBD system includes several diagnostic devices that monitor individual parameters of the toxicity reduction systems and record detected failures in the on-board processor memory in the form of individual fault codes. The system also checks sensors and actuators, monitors vehicle maintenance cycles, and provides the ability to memorize even short-term failures during operation and clear the memory block.

Some of the models described in this Manual are equipped with an on-board diagnostics system. The main element of the system is the on-board processor, more often called the electronic control module (ECM) or the powertrain control module (PCM). The PCM is the brain of the engine management system. Initial data comes to the module from various information sensors and other electronic components (switches, relays, etc.).



Based on the analysis of data received from information sensors, and in accordance with the basic parameters stored in the processor memory, the RCM generates commands to operate various control relays and actuators, thereby adjusting the engine operating parameters and ensuring maximum efficiency with minimal fuel consumption.

Reading the OBD processor memory data is performed using a special scanner connected to the 20-pin diagnostic connector located on the left in the engine compartment.

The black, 20-pin X 1532 diagnostic connector is located in the left rear of the engine compartment, to the right of the shock absorber dome (arrow). M30 engine shown

In principle, reading the fault codes stored in the memory of the self-diagnostic system can be done using the "Check Engine" lamp (refer to the section Reading fault codes).

Pin assignment of the 20-pin diagnostic connector

Information sensors

Oxygen sensors (lambda probes) - The sensor generates a signal, the amplitude of which depends on the difference in oxygen content (O2) in the engine exhaust gases and the outside air before and after the catalytic converter.

Crankshaft position sensor (CPS) - The sensor informs the PCM about the position of the crankshaft and engine speed. This information is used by the processor when determining the fuel injection moments and setting the ignition timing.

Piston Position Sensor (CYP) - Based on the analysis of signals received from the sensor, the RCM calculates the position of the piston of the first cylinder and uses this information to determine the timing and sequence of fuel injection into the engine combustion chambers.

TDC sensor - The signals generated by the sensor are used by the PCM to determine the ignition timing settings at the moment of engine start.

Engine Coolant Temperature (ECT) Sensor - Based on the information received from the sensor, the ECM/PCM makes the necessary adjustments to the air-fuel mixture composition and ignition timing, and also monitors the operation of the EGR system.

Intake Air Temperature (IAT) Sensor - The PCM uses the information received from the IAT sensor to make fuel flow adjustments, set the ignition timing and control the operation of the EGR system.

Throttle Position Sensor (TPS) - The sensor is located on the throttle body and is connected to the throttle shaft. Based on the amplitude of the signal emitted by the TPS, the PCM determines the throttle opening angle (controlled by the driver using the gas pedal) and accordingly adjusts the fuel supply to the combustion chamber intake ports. Sensor failure or loosening of its fastening leads to injection interruptions and disturbances in the stability of idle speed.

Absolute pressure sensor in the pipeline (MAP) - The sensor monitors variations in the vacuum depth in the intake manifold associated with changes in crankshaft speed and engine load and converts the information received into an amplitude signal. The PCM uses the information supplied by the MAP and IAT sensors for fine adjustments to fuel delivery.

Atmospheric pressure sensor - The sensor generates an amplitude signal proportional to changes in atmospheric pressure, which is used by the PCM to determine the duration of fuel injection moments. The sensor is built into the PCM module and is not subject to individual maintenance.

Knock sensor - The sensor reacts to changes in the vibration level associated with detonations in the engine. Based on the information received from the sensor, the PCM makes the appropriate adjustment of the ignition advance angle.

Vehicle Speed Sensor (VSS) - As its name suggests, the sensor informs the processor about the current speed of the vehicle.

EGR valve opening value sensor - The sensor notifies the PCM of the amount of displacement of the EGR valve plunger. The received information is then used by the processor to control the operation of the exhaust gas recirculation system.

Fuel tank pressure sensor - The sensor is a component of the fuel vapor trapping system (EVAP) and serves to monitor the pressure of gasoline vapors in the tank. Based on the information received from the sensor, the PCM issues commands to operate the electromagnetic valves for purging the system.

Power Steering Pressure Switch (PSP) - Based on the information received from the PSP switch sensor, the PCM increases the idle speed by activating the IAC sensor in order to compensate for the increasing loads on the engine associated with the operation of the power steering during maneuvers.

Transmission sensors - In addition to the data received from the VSS, the PCM also receives information from sensors located inside or connected to the transmission. These sensors include: (a) the secondary (main) shaft speed sensor and (b) the intermediate shaft speed sensor.

Air Conditioner Clutch Control Switch Sensor - When power is supplied from the battery to the electromagnetic valve of the K/V compressor, the corresponding information signal is sent to the PCM, which evaluates it as evidence of an increase in the load on the engine and adjusts its idle speed accordingly.

Executive devices

PGM-FI Main Relay (fuel pump relay) - The PCM activates the fuel pump relay when the ignition key is turned to the START or RUN position. When the ignition is turned on, the relay is activated to increase the pressure in the fuel system. More detailed information on the main relay is provided in Chapter Power supply system.

Fuel injectors - The PCM ensures individual activation of each injector in accordance with the established ignition sequence. In addition, the module controls the duration of the injector opening, determined by the width of the control pulse, measured in milliseconds and determining the amount of fuel injected into the cylinder. More detailed information on the operating principle of the injection system, replacement and maintenance of injectors is given in Chapter Power supply system.

Ignition Control Module (ICM) - The module controls the operation of the ignition coil, determining the required basic advance based on the commands generated by the PCM. All vehicle models discussed in this Manual use an ICM built into the ignition distributor, for more details see Chapter Ignition system.

Idle Air Control Valve (IAC) - The IAC valve controls the amount of air bypassed through the throttle valve when the latter is closed or in the idle position. The PCM controls the opening of the valve and the formation of the resulting air flow.

Carbon adsorber purge solenoid valve - The valve is an integral part of the fuel evaporative emission (EVAP) system and, when triggered by the PCM, releases the fuel vapors accumulated in the adsorber into the intake manifold for the purpose of burning them during normal engine operation.

Carbon adsorber purge control solenoid - The solenoid is used by the PCM when the OBD-II system checks for proper operation of the EVAP system.

Reading fault codes

If a fault is detected that is repeated in two consecutive trips, the PCM issues a command to turn on the "Check Engine" warning lamp, also called the malfunction indicator, built into the instrument cluster. The lamp will remain lit until the memory of the self-diagnostic system is cleared of the codes of detected faults stored in it. Reading fault codes in the OBD system can be done in various ways. The main method is reading using the devices described above, connected to the DLC connector of the OBD system. Other methods are not available on all models. The flashing code can be read from the "Check Engine" lamp.

Without starting the engine, turn on the ignition - the "Check Engine" indicator light should light up, otherwise it should be replaced.

On early models, if there is a fault, the indicator lamp will flash several times for 1 second and go out before coming on continuously. The number of flashes of the lamp (from 1 to 4) corresponds to the fault code (list below).

Method for reading flashing codes from the "Check engine" lamp (possible on some models)

Flashing code output diagram for the control lamp



Turn on the ignition. Fully depress and release the accelerator pedal five times within five seconds. If the processor memory contains codes of previous malfunctions, they will begin to be sequentially displayed by the "Check Engine" indicator lamp on the vehicle's dashboard. Read the flashing code.

The lamp lights up for 5 seconds, lights up again for 2.5 seconds after 0.5 seconds, and a code is issued after an interval of 2.5 seconds. The value of each code digit corresponds to the number of flashes with an interval of 0.5 seconds. The most significant digits of the code are issued first, and the ones are issued last. The intervals between code digits are 2.5 seconds. After the code is issued, the lamp remains lit. Repeat the procedure to read subsequent codes. If the first code issued is 1444, 2444 or 4444, no faults have been recorded.

Codes 1000 or 2000, given by one or two flashes and a long pause, followed by a constant lamp glow, indicate the end of the code output.

Starting the engine automatically interrupts access to the diagnostic system.

Clear OBD memory

When a fault code is entered into the PCM memory, the "Check Engine" indicator light on the vehicle's instrument panel lights up. The code remains stored in the module's memory.

To clear the ECM memory, connect a scanner to the system and select the CLEARING COEDS function in its menu (Removing codes). Next, follow the instructions displayed on the device, or immediately remove the EFI fuse from its socket in the fuse box for 30 seconds.

Alternatively, clearing the system memory can be done by removing the fuse link (main fuse of the on-board electrical system), installed near the positive terminal of the battery (you can also simply disconnect the positive cable from the battery).

It should be noted that clearing the OBD memory by disconnecting the negative battery cable will erase the engine settings and disrupt the stability of its speed for a short time after the initial start.

If your car stereo system is equipped with a security code, make sure you have the correct combination to activate the audio system before disconnecting the battery!

Disconnecting the battery also erases your receiver's favorite radio station settings.

To avoid damaging the ECM, disconnect and connect it only with the ignition off!

Make sure that the system memory is cleared before installing new emission control components on the engine. If the fault memory is not cleared before starting the system after replacing a failed information sensor, the PCM will enter a new fault code. Clearing the memory allows the processor to reconfigure to the new parameters. However, in the first 50 to 20 minutes after the initial start of the engine, some disruption of the stability of its speed may occur.

Error codes

Motronic 1.1, 1.2, 1.3 – failure lamp flashes

1	Air flow sensor
2	Lambda probe
3	Coolant temperature sensor
4	Throttle Closed Position Switch

Motronic 1.1, 1.2, 1.3

1	Electronic control unit
3	Fuel Pump Relay Circuit
5	Idle Speed Control Valve Circuit
7	Air flow meter
10	Mixture quality control, lambda sensor
15	Failure indicator light
16	Injectors cylinders 1, 3, 5
17	Injectors for cylinders 2, 4, 6
23	Heating of the lambda probe or its relay
28	Lambda probe circuit
29	Engine speed sensor
33	Kick-down valve
37	Power supply of the electronic control unit is higher than 16V
43	CO adjustment potentiometer
44	Air temperature sensor
45	Coolant temperature sensor
51	Ignition timing offset
52	Throttle Position Limit Switch
53	Throttle Position Limit Switch
54	AT rotation converter lock
100	Ignition booster
101	Engine failure

Diagnostic codes for DME 1.7 (518i) systems, read using a tester

1	Fuel pump relay or its circuit to the control unit (terminal 1)
3	Open circuit, short circuit in injectors 1 and 3
8	Short circuit of the "Check engine" warning lamp circuit
12	Open circuit, short circuit in the throttle potentiometer circuit
16	Camshaft position sensor. Signal disappears at 2500 rpm.
29	Short circuit in the idle control circuit (terminal 29)
32	Open circuit, short circuit in injectors 2 and 4
36	Open circuit, short circuit in the fuel tank ventilation valve circuit
37	Open circuit, short circuit of the lambda probe heating circuit (terminal 37)
41	Open circuit, short circuit in the air flow meter circuit
54	The control unit supply voltage is below 9V or above 16V
70	Open circuit, short circuit of the lambda probe circuit
73	Incorrect vehicle speed sensor signal
77	Open circuit, short circuit in the intake air temperature sensor circuit
78	Open circuit, short circuit in the coolant temperature sensor circuit
85	Air conditioning compressor. Open circuit at terminal 86 and short circuit at terminal 85
100	Lost connection of ignition output signal from final stage
200	Internal memory defect of the control unit
201	Too rich or too lean mixture in the last 8 seconds

Diagnostic codes for DME 3.1 systems (520i, 525), read using a tester

0	Unspecified fault in the memory unit
1	Fuel pump relay or its circuit to the control unit (terminal 1)
2	Open circuit, short circuit of the idle speed actuator (closed) or its circuit to the control unit (terminal 2)
3	Open circuit, short circuit in the injector 1 circuit to the control unit (terminal 3)
4	Open circuit, short circuit in the injector 3 circuit to the control unit (terminal 4)
5	Open circuit, short circuit in the injector 2 circuit to the control unit (terminal 5)
6	Open or short circuit in injector circuits
8	Open or short circuit of the "Check engine" warning lamp circuit
12	Open or short circuit in the throttle potentiometer circuit
16	Camshaft Position Sensor Signal
18	Short circuit to the housing or positive terminal 18 of the control unit
19	Short circuit to the housing or positive terminal 19 of the control unit
23	Open circuit of ignition coil output of cylinder 2 (terminal 23)
24	Open circuit of ignition coil output of cylinder 3 (terminal 24)
25	Open circuit of ignition coil output of cylinder 1 (terminal 25)
26	The control unit supply voltage is lower than the battery voltage (with the engine off)
29	Short circuit in the idle speed actuator circuit (open), (terminal 29)
31	Open circuit, short circuit in the injector 5 circuit to the control unit (terminal 31)
32	Open circuit, short circuit in the injector 6 circuit to the control unit (terminal 32)
33	Open circuit, short circuit in the injector 4 circuit to the control unit (terminal 33)
34	Open circuit, short circuit of component circuits to the control unit
36	Open circuit, short circuit in the fuel tank ventilation valve circuit
37	Open circuit, short circuit in the lambda probe heating circuit
41	Open circuit, short circuit in the air mass meter circuit
46	Short circuit to the housing or positive terminal 46 of the control unit
48	Air conditioning compressor does not turn off at speeds below 8 km/h
50	Open circuit of ignition coil output of cylinder 4 (terminal 50)
51	Open circuit of the ignition coil output of cylinder 6 (terminal 51)
52	Open circuit of ignition coil output of cylinder 5 (terminal 52)
54	The control unit supply voltage is below 10V or above 14V
55	Open circuit in ignition circuits
64	Ignition advance circuit - short circuit to the body of terminal 64 of the control unit
67	No signal from the crankshaft speed/position sensor, Ignition and injection are off
70	Open circuit, short circuit of the lambda probe circuit
73	Vehicle speed sensor
77	Open circuit, short circuit in the intake air temperature sensor circuit
78	Open circuit, short circuit in the coolant temperature sensor circuit
81	Anti-theft alarm triggered after engine start
85	Air conditioning compressor operates after engine start, while no switch signal was received
100	Short circuit to the housing or positive terminal 100 of the control unit
200	Internal defect of RAM or ROM/EPROM of the control unit
201	Internal fault memory defect
202	Emission control systems out of control

Diagnostic codes for Motronic M3.3 (540i) systems

1211	Engine control unit
1212	Lambda probe 2
1213	Lambda probe signal control limits 2 exceeded
1215	Air mass/air flow meter
1216	Throttle potentiometer
1221	Lambda probe 1
1222	Lambda probe signal control limits 1 exceeded
1223	Coolant temperature sensor
1224	Intake air temperature sensor
1225	Knock Sensor 1
1226	Knock Sensor 2
1227	Knock Sensor 3
1228	Knock Sensor 4
1231	Supply voltage
1232	Throttle Closed Position Switch
1233	Fully Open Throttle Position Switch
1237	Air Conditioning Pump Relay
1243	No engine speed sensor signal
1244	Camshaft position sensor
1247	Connection to the engine control unit housing
1251	Injector cylinder 1
1252	Injector cylinder 5
1253	Cylinder 4 injector
1254	Cylinder 8 injector
1255	Cylinder 6 injector
1256	Injector cylinder 3
1257	Cylinder 7 injector
1258	Injector cylinder 2
1261	Fuel pump relay
1262	Idle speed control valve.
1263	Evaporative Canister Purge Valve
1264	Lambda probe heating relay
1265	Short circuit in the fault indicator lamp circuit
1267	Air pump
1271	Ignition coil cylinder 1
1272	Ignition coil cylinder 5
1273	Ignition coil cylinder 4
1274	Ignition coil cylinder 8
1275	Ignition coil cylinder 6
1276	Ignition coil cylinder 3
1277	Ignition coil cylinder 7
1278	Ignition coil cylinder 2
1281	Low voltage supply to the engine control unit
1282	Engine control unit memory fault
1283	Connecting the injector to the body
1286	Knock control circuit
1444	No registered faults

Automatic transmission diagnostic codes stored in the control unit memory

1	Transmission relay
2	EPROM memory checksum
3	Kick-down switch
4	Program switch
5	Accelerator pedal signal, throttle signal
6	Solenoid valve solenoid valve 1
7	Solenoid valve solenoid valve 2
8	Solenoid valve 1, Solenoid valve 2
9	P/N shift solenoid blocked
10	Solenoid valve 1, switching solenoid P/ blocked
11	Solenoid valve 2, P/N switching solenoid blocked
12	Solenoid valve 1, solenoid valve 2, switching solenoid P/ blocked
13	Rotary Converter Clutch Solenoid Valve
14	Solenoid valve 1, solenoid valve of the rotation converter clutch
15	Solenoid valve 2, solenoid valve of the rotation converter clutch
16	Solenoid valve 1, solenoid valve 2, solenoid valve of the rotation converter clutch
17	P/N shift solenoid blocked, torque converter clutch solenoid valve
18	Solenoid valve 1, P/N shift solenoid blocked, torque converter clutch solenoid valve
19	Solenoid valve 2, P/N shift solenoid blocked, torque converter clutch solenoid valve
20	Supply voltage of the solenoid valve and pressure regulator (DR)
21	Engine RPM Reference Signal (1 per crankshaft revolution)
22	Pressure regulator
23	Interference with ignition timing adjustment
24	Output RPM Sensor, Downshift Blocked
25	Overrev protection
26	Injection signal (ti)
27	Output speed sensor (DZF) or rotation converter
28	Malfunction indicator (except GS 1.2)
29	Program checksum
30	Battery supply voltage
31	Selector lever position

Automatic transmission diagnostic codes not stored in the control unit memory, determined during monitoring

200	Kick-down switching is missing
201	Switching only kick - down
202	S program is missing
203	M program is missing
204	Program switching does not occur
205	No engine intervention
206	Incorrect display of faults
207	Shifts only under full load (no EML)
300	Diagnostic line failure
301	Control unit supply voltage deviation
302	Selector lever position
303	The position of the selector lever is not detected

Automatic Cabin Air Conditioner Diagnostic Codes

01	Right temperature control knob
04	Right heating sensor
07	Evaporator sensor
10	Outside air temperature sensor
13	Interior sensor
16	Interior Fan Sensor
22	Additional fan relay (Clutch relay KV - DME)
25	Left temperature control knob
28	Left heating sensor
31	Air flow control
32	Air flow selector lever to the feet
34	Air mixing control
38	Additional water pump relay
40	Left water valve
44	Relay KV/Stage 1 additional fan
46	Right water valve
47	Clutch relay KV DME/EML
48	Rear window heating relay
52	Fresh air flap motor
55	Air circulating damper motor
58	Left ventilation flap motor
61	Right mixed air flap motor
64	Left mixed air flap motor
67	Rear Cabin Flap Motor
70	Left footwell air flow flap motor
73	Motor of the right air flow flap to the feet
76	Defrost flap motor
79	Right ventilation flap motor