OBD system — general information

The material below is descriptive only and is not tied to any particular make or model of vehicle.

Information about diagnostic tools

Checking the correct functioning of the components of the injection systems and reducing the toxicity of exhaust gases is carried out using a universal digital meter (multimeter). The use of a digital meter is preferred for several reasons. Firstly, it is quite difficult for analog devices to (sometimes impossible), to determine the result of the indication with an accuracy of hundredths and thousandths, while when examining circuits that include electronic components, such accuracy is of particular importance. The second, no less important, reason is the fact that the internal circuit of a digital multimeter has a fairly high impedance (the internal resistance of the device is 10 million ohms). Since the voltmeter is connected in parallel to the circuit under test, the measurement accuracy is the higher, the less parasitic current will pass through the device itself. This factor is not significant when measuring relatively high voltage values (9-12 V), however, it becomes decisive in the diagnosis of elements that produce low-voltage signals, such as, for example, a lambda probe, where we are talking about measuring fractions of a volt.


The most convenient devices for diagnosing engine control systems of modern car models are manual scanner-type readers. First generation scanners are used to read fault codes for OBD-I systems. Before use, the reader should be checked for compliance with the model and year of manufacture of the vehicle being checked. Some scanners are multifunctional due to the possibility of changing the cartridge depending on the model of the car being diagnosed (Ford, GM, Chrysler, etc.), others are tied to the requirements of regional authorities and are intended for use in certain areas of the world (Europe, Asia, USA, etc.).



Recently, reading devices such as hand-held scanners such as Actron Scantool or AutoXray XP240 have become absolutely indispensable for diagnosing engine control systems of modern cars.



Diagnostic scanner New Generation Star (NGS) (The scanners FDS 2000, Bosch FSA 560 [www.bosch.de] and KTS 500 [0 684 400 500] are also widely used).


With the introduction of a second-generation on-board diagnostic system that meets the latest environmental legislation (OBD-II) Readers of a special design began to be produced. Some manufacturers have launched scanners designed for use by amateur mechanics at home - ask in car accessories stores.





Another very convenient diagnostic tool is the expensive specialized diagnostic computer of the ADC2000 type from Launch HiTech), or a regular personal computer complete with a special cable and adapter (set 1 687 001 439).

The adapter is designed to match the diagnostic lines K and L (see illustration OBD II system diagnostic connector, - when connecting, use a standard OBD-II J1962 cable) with the computer's COM port.


Some scanners, in addition to the usual diagnostic operations, allow, when connected to a personal computer, to print circuit diagrams of electrical equipment stored in the memory of the control module (if any), program the anti-theft system, observe the signals in the fuse circuits in real time.

A free version of the OBD II browser can be downloaded from the website of the compilers of this Manual arus.spb.ru.

In principle, reading the fault codes recorded in the memory of the self-diagnosis system can be done using the MIL failure indicator lamp and a jumper wire installed between specific terminals of the 16-pin diagnostic connector.

General description of the OBD system

OBD II system diagnostic connector, - when connecting, use a standard OBD-II J1962 cable

The purpose of some of the pins of the standard 16-pin DLC connector of the OBD II system:

On OBD II-equipped modules, the nameplate under the hood must have an entry «OBD II compliant», and the DLC diagnostic connector must be 16-pin. As a rule, the OBD II system is mandatory for North American models from 1996 and European models from 2000 onwards.

The OBD system includes several diagnostic devices that monitor individual parameters of the toxicity reduction systems and fix the detected failures in the on-board processor memory in the form of individual fault codes. The system also checks sensors and actuators, controls the vehicle's operating cycles, provides the possibility of freezing parameters and clearing the memory block.

All models described in this manual are equipped with a second generation on-board diagnostic system (OBD-II). The main element of the system is the onboard processor, often called the electronic control module (ECM). The ECM is the brain of the engine management system. The initial data is fed to the module from various information sensors and other electronic components (switches, relays, etc.). Based on the analysis of the data coming from the information sensors and in accordance with the basic parameters stored in the processor memory, the ECM generates commands for the operation of various control relays and actuators, thereby adjusting the engine's operating parameters and ensuring maximum engine efficiency with minimum fuel consumption. The OBD-II processor memory data is read using a special scanner connected to the 16-pin diagnostic connector for reading the database (DLC), located under the decorative cover on the center console in front of the parking brake lever (see illustrations The DLC diagnostic connector is located in the center console in front of the parking brake lever under a decorative cover, Location of the DLC connector in the console and OBD II system diagnostic connector, - when connecting, use a standard OBD-II J1962 cable).

In principle, reading the fault codes recorded in the memory of the self-diagnosis system can be done using a jumper wire installed between specific terminals of the 16-pin diagnostic connector.

Engine management/emission control system components are subject to a special extended warranty. You should not attempt to independently diagnose ECM failures or replace system components until the expiration of these obligations - contact Opel branded service stations.

Information sensors (depending on vehicle configuration)

Oxygen sensors (lambda probes)

The sensor generates a signal whose amplitude depends on the difference in oxygen content (O2) in engine exhaust gases and outside air.

Crankshaft position sensor (TFR)

The sensor informs the ECM about the crankshaft position and engine speed. This information is used by the processor when determining fuel injection timing and setting the ignition timing.

Piston position sensor (CYP)

Based on the analysis of the signals from the sensor, the ECM 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's combustion chambers.

TDC sensor (TDC)

The signals generated by the sensor are used by the ECM in determining ignition timing settings at the time of engine start.

Engine coolant temperature sensor (EATING)

Based on the information coming from the sensor, the ECM / makes the necessary adjustments to the composition of the air-fuel mixture and the ignition timing, and also monitors the operation of the EGR system.

Intake air temperature sensor (IAT)

The ECM uses information from the IAT sensor to make adjustments to fuel flow, ignition timing, and EGR system operation.

Throttle position sensor (TPS)

The sensor is located on the throttle body and is connected to the throttle valve shaft. From the amplitude of the TPS signal output, the ECM determines the throttle opening angle (controlled by the driver from the gas pedal) and adjusts the fuel supply to the inlet ports of the combustion chambers accordingly. The failure of the sensor, or the weakening of its fastening, leads to interruptions in injection and violations of the stability of the idle speed.

Absolute pressure sensor in the pipeline (IDA)

The sensor monitors variations in the depth of depression in the intake manifold associated with changes in crankshaft speed and engine load and converts the information received into an amplitude signal. The ECM uses the information provided by the MAP and IAT sensors to make subtle fuel adjustments.

Atmospheric pressure sensor (BARO)

The sensor produces an amplitude signal proportional to changes in atmospheric pressure, which is used by the ECM to determine the length of the fuel injection timings. The sensor is built into the ECM and is not individually serviceable.

Knock sensor (KS)

The sensor reacts to changes in the level of vibrations associated with detonations in the engine. Based on the information from the sensor, the ECM adjusts the ignition timing accordingly.

Vehicle speed sensor (VSS)

As its name implies, the sensor informs the processor about the current vehicle speed.

EGR valve opening sensor

The sensor notifies the ECM of the amount of displacement of the EGR valve plunger. The information received is then used by the processor when controlling the operation of the exhaust gas recirculation system.

Fuel tank pressure sensor

The sensor is an integral part of the fuel vapor recovery system (EVAP) and serves to monitor the vapor pressure of gasoline in the tank. Based on the information coming from the sensor, the ECM issues commands to operate the system purge solenoid valves.

Power steering pressure switch (PSP)

Based on information from the PSP sensor-switch, the ECM provides an increase in idle speed due to the activation of the idle speed stabilization system sensor (IAC) 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 coming from the VSS, the ECM also receives information from sensors placed inside the transmission or connected to it. These sensors include:

• secondary speed sensor (indigenous) shaft
• intermediate shaft speed sensor.

Sensor-switch for controlling the inclusion of the clutch clutch of the air conditioner

When battery power is applied to the A/C compressor solenoid valve, the corresponding information signal is sent to the ECM, which regards it as evidence of an increase in engine load and adjusts its idle speed accordingly.

Executive devices

Fuel pump relay

The ECM activates the fuel pump relay when the ignition key is turned to the START or RUN position. When the ignition is turned on, the activation of the relay provides a pressure rise in the power system. For more information on the main relay, see Chapter Power and exhaust systems.

Injector (s) fuel

The ECM ensures that each of the injectors is turned on individually in accordance with the established firing order. In addition, the module controls the duration of the opening of the injectors, determined by the width of the control pulse, measured in milliseconds, which determines the amount of fuel injected into the cylinder. More detailed information on the principle of operation of the injection system, replacement and maintenance of injectors is given in Chapter Power and exhaust systems.

Ignition control module (ICM)

The module controls the operation of the ignition coil by determining the required base advance based on commands issued by the ECM.

Idle speed control valve (IAC)

The IAC valve controls the amount of air that bypasses the throttle when the throttle is closed or in the idle position. The opening of the valve and the formation of the resulting air flow is controlled by the ECM.

Carbon canister purge solenoid valve

The valve is an integral part of the fuel vapor recovery system (EVAP) and, triggered by the ECM command, releases the accumulated fuel vapors in the adsorber into the inlet pipeline in order to burn them during the normal operation of the engine.

Carbon canister purge control solenoid

The solenoid is used by the ECM when the OBD-II system checks that the EVAP system is functioning properly.

Reading fault codes and clearing processor memory

If a malfunction is detected that repeats in a row in the spirit of trips, the ECM issues a command to turn on the warning lamp built into the instrument panel «Check engine», also called the failure indicator (MIL). At the same time, the control unit switches to emergency mode. The lamp will continue to burn until the memory of the self-diagnosis system is cleared of the fault codes entered in it (see below).

Reading codes with a scanner

Fault codes are read by connecting a special reader (see above) to the 16-pin DLC diagnostic connector (see illustrations The DLC diagnostic connector is located in the center console in front of the parking brake lever under a decorative cover, Location of the DLC connector in the console and OBD II system diagnostic connector, - when connecting, use a standard OBD-II J1962 cable), - follow the instructions in the device menu. The list of codes is given in Specifications.

Reading Codes with the MIL

1. Stop the engine and turn off the ignition. Open the decorative cover of the center console in front of the parking brake lever (see illustrations The DLC diagnostic connector is located in the center console in front of the parking brake lever under a decorative cover and Location of the DLC connector in the console) and short to ground terminal 6 (or 5) 16-pin DLC diagnostic connector, - proceed very carefully, try not to bend the terminals. It should be remembered that bad contacts in the terminal connections can cause failure of the control module, or malfunction of the processor memory.



2. Turn on the ignition. The diagnostic codes stored in the memory of the control module are read by flashes produced by the MIL / «Check engine» on the dashboard of a car (see chapter Manual).

3. Each fault code consists of four groups of flashes (discharges). The number of flashes in the group corresponds to the value of the code bit. A short pause separates the bits of the code, a long pause serves to separate the codes. Each code is displayed three times in a row. Codes are issued in ascending order of numbers. Zero corresponds to 10 flashes of the control lamp.

4. The highlighted code allows you to determine only the circuit of the system, the failure of which was recorded by the self-diagnosis system. So, if the code indicates a malfunction of the coolant temperature sensor (ECT), the possibility of malfunctioning of the control module itself is not excluded. You can establish the truth either by replacing the sensor, or by conducting appropriate control measurements.

5. When checking the circuit, first of all, disconnect the corresponding electrical wiring and check the condition of its contact connections. If necessary, clean the terminals, completely removing traces of oxidation from them.

6. Check that the cable is securely attached to the cable lug.

7. Check the resistance of the suspect element - if the nominal resistance of the element is low, factors such as accuracy and internal resistance of the meter should be taken into account.

8. Check the integrity of the wires going to the control module (if necessary, check the wiring diagrams - see Chapter Onboard electrical equipment).

When reading codes indicating an excessive underestimation of the signal level, first of all, you need to make sure that the ground of the corresponding component is reliable. An overestimation of the signal level is most often associated with a broken electrical wiring.

Information content of bits of a 5-bit code of the form P0380

View code bits R 0 3 8 0 have the following meaning (from left to right):

1 rank (left)	Code source
P	power unit
B	body
WITH	chassis
2nd category	Code source
0	standard SAE
1	advanced - manufacturer-specified
3rd category	System
0	system as a whole
1	air mixing (air/fuel induction)
2	fuel injection
3	ignition system or misfiring
4	additional release control (auxillary emission control)
5	vehicle speed and idle control
6	input and output signals of the control unit
7	transmission
4.5 digits	Sequence number of component or circuit failure (00-99)

Clearing the OBD II memory

To clear the ECM memory, turn off the ignition, remove the jumper that grounds the DLC connector, and disconnect the battery terminal for at least 60 seconds, or connect a scanner to the system and select the CLEARING CODES function in its menu (Deleting codes), - then follow the instructions displayed on the device.

Clearing the OBD memory by disconnecting the negative cable from the battery is associated with the removal of the engine settings and the violation of the stability of its revolutions for a short time after the initial start, as well as erasing the clock and radio settings.

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

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

The code stored in the memory is deleted automatically if the corresponding malfunction does not appear within 20 successive engine starts (the number of revolutions must be at least 450 per minute).

Make sure that the system memory is cleared before installing new emission control system components on the engine. If the fault memory is not cleared before starting the system after replacing a failed information sensor, the ECM will store a new fault code in it. Clearing memory allows the processor to reconfigure to new parameters. In this case, the first 15-20 minutes after the initial start of the engine until the end of the ECM adaptation, there may be some violation of the stability of its revolutions.