What is automatic on-board diagnostic system OBD?

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1 board diagnostics system OBD

OBD is the abbreviation of the English On-Board Diagnostics, the Chinese translation for the ldquo; board diagnostics system rdquo ;. The system will monitor the operating conditions of the engine at any time whether excessive vehicle exhaust, once exceeded, a warning will be issued immediately. When the system fails, the failure (MIL) lamp or check engine (Check Engine) warning light, while the powertrain control module (PCM) fault information stored in the memory, can be read out from the PCM fault code through certain procedures . The prompt fault code, maintenance personnel can quickly and accurately determine the nature and location of the fault.

OBD Principle

OBD real-time monitoring of the engine, catalytic converter, particulate trap, an oxygen sensor, the emission control system, fuel system, and other systems and components of the EGR . Then different information related to the discharge member, coupled to the electronic control unit [ECU, it can detect, analyze the function associated with the discharge failure], when discharge failure occurs, recording the fault information and related ECU code and emitted by the lamp failure warning, inform the driver. ECU via standard data interface, to ensure the access and processing fault information.

Function of OBD Ⅱ

After the program OBD Ⅱ embodiment, a technician may use any of a single diagnostic instrument in accordance with any diagnostic standard production cars. One OBD Ⅱ mature functional when the system fault light is lit, all the data recording sensors and actuators, the diagnosis can best meet the need for maintenance. States face increasingly stringent vehicle emission regulations, OBD Ⅱ emission control monitoring system efficiency goal is: With the loss in efficiency of the car is running, according to the Federal Test Procedure, when the vehicle emission level has reached a new car emission standards of 1.5 times lighting the lamp failure and fault code memory. In addition, OBDⅡ requestedSome additional sensor hardware configuration, such as additional heating an oxygen sensor disposed downstream of the catalytic converter in the exhaust gas. More sophisticated use of a crankshaft or camshaft position sensor, in order to more accurately detect whether misfire, a new model configuration of all 16-pin diagnostic interface. As a result, the capacity of the computer is greatly improved, not only to track the damaged parts, but also meets the stringent restrictions on vehicle emissions.

OBD Ⅱ standardized

OBD Ⅱ process design requirements to avoid confusion between systems, which not only requires the use of a standard 16-pin diagnostic interface, but also the use of specific code and description of parts in the manufacturer’s file, which is to achieve harmonization and standardization of the following aspects. Means

(1) General terms and acronyms

For example, to provide crankshaft position and speed information for the computer is called a crank position sensor, abbreviations are ldquo; CKPrdquo ;, said computers are unified as ldquo; PCMrdquo ;.

(2) General Data diagnostic interface

Each car is equipped with a standard shape and size 16-pin diagnostic interface, the same for each pin signal distribution, and at the same position, installed in the instrument under disc, somewhere between the dashboard and the car left the center line of the right of 300mm. It should be noted that some of the terminals are diagnostic interface, designated as a specific signal as shown in the table. While other terminals may allow manufacturers to use, or not used in current car models.

(3) the Generic Diagnostic Test Mode

test patterns, all of the cars are common OBD Ⅱ using OBD Ⅱ scan tool can be tested.

(4) General Scan Tool

satisfies the scan tool OBD Ⅱ requirements, must pass through to access and interpret any vehicle emissions related diagnostic trouble codes, the scanning tool has a wire harness with a standard 16-pin connector contact.

(5) General diagnostic trouble code

At the time of Shanghai Buick, Guangzhou Accord other car fault diagnosis, self-diagnosis system can display standard OBD Ⅱ Fault codes, such as ldquo; PO125rdquo; , ldquo; PO204rdquo ;, represent the speed signal when the engine does not reach 10 deg.] C 5min injector 4 and the output driver in response to the control signal incorrectly.

SAE J2010 standard provides for a five fault code, bit 1 is the letter followed by four numbers.

represents the first letter of the code is provided a system failure. There are currently assigned letters 4: ldquo; Prdquo; representative of the power system, ldquo; Brdquo; representative of the vehicle body, ldquo; Crdquo; Representative chassis, ldquo; urdquo; Representative undefined system.

The first two characters are 1, 2 or 3, meaning as follows:

0mdash; mdash; generic fault codes SAE (Society of Automotive Engineers) defined: 1mdash; mdash; car extended fault codes defined by the manufacturer. 2 or 3mdash; mdash; character with the system (P, B, C or U) differ. Power system fault code (P) is reserved for future use 2 or 3 of the SAE; a vehicle body or chassis fault codes reserved for the factory 2, the vehicle body or chassis fault code 3 retained by SAE.

bit 3 shows character system failure: 1mdash; mdash; fuel or air metering failures; 2mdash; mdash; fuel or air metering failures; 3mdash; mdash; engine misfire or an ignition failure; 4mdash; mdash ; secondary emission control system failure; 5mdash; mdash; automobile or idling control system failure; 6mdash; mdash; a computer or an output circuit fault. 7mdash; mdash; transmission control system; 8mdash; mdash; transmission control system.

The last two characters represent triggers a fault code. Various sensors, actuators and digital circuits assigned different sections, a small section of a digital representation of general fault, i.e. general fault codes; spreading codes with a higher number provides more specific information, such as low voltage or high, slow response, or out of range signal.

(6) a standardized protocol

requires the manufacturer to use the same multiplex communication language, forPCM communication between its sensors and actuators, and sending and receiving diagnostic information between the diagnostic tool.

OBD Ⅱ standard requirements, depending on the operating conditions of the warm-up period is specifically set, the driving cycle, the OBD Ⅱ stroke, the OBD Ⅱ driving period, and similar conditions such as the engine management system to each other by the monitoring circuit, monitoring detecting the failure sequence, the position of the fault codes, fault lights on and off, and the fault code erasing. Here, the operation sequence is a monitoring process, is used to test a predetermined operating system functions or components. Example, a computer can be opened at the time of deceleration or closes the EGR valve, and monitors the MAP sensor to observe the EGR valve is working; or while cruising, the computer opens or closes the canister purge to observed signals oxygen sensor, so can test simultaneously two members.

Scan Tool

OBD Ⅱ regulations fault codes, a large amount of engine management sensor signals, the computer commands, etc., can be read out by a common scanning tool . Scanning tools can give a lot of important maintenance information, but a lot of maintenance personnel did not use its full functionality, only read fault codes. In fact, the scan data provided tools, most can be used to detect failures. Troubleshooting a particularly effective method is to use a scan tool and tetrakis gas (HC, CO, oxygen and carbon dioxide) gas or five (plus NOx) infrared type exhaust gas analyzer. This command information and the actual exhaust tail pipe of the sensor signal or a computer compared to see the logical result of these readings is reasonable.

relevant information

2006 December 1, Beijing has banned the installation of OBD does not prohibit the sale of vehicles in Beijing.

In July 2008, have been implemented nationwide installation of vehicle OBD.

OBDII diagnostic car seat 16 defined in the needle hub

OBD system fault should be treated

OBD system after a failure promptly repaired. Vehicle inspection once a year for vehicle emission control role is limited. But after the installation of OBD car is completely different, and it can monitor emission levels of vehicles at any time.

If once the emissions of non-compliance, OBD warning will be issued promptly notify the driver to repair. Euro Ⅲ The key is to use the OBD.

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