CEL
From Wikifixx
Check Engine Light
 | |
| Type | Government Mandate |
|---|---|
| Founded | 1995 |
| Founder(s) | US Government |
| Headquarters | Washington D.C., USA |
| Area served | Worldwide |
| Industry | Automotive |
| Products | Cars |
| Website | Ross Tech |
Vehicles from 1996 and on are equipped with a computer that can store Diagnostic Trouble Codes (DTCs). This system monitors the functionality of many systems in the automobile, and the overall health of the engine. These codes are read with a scan tool that plugs into the car's OBD port. Scan tools can be borrowed from an Advanced Auto Parts for free, but they sometimes have a problem reading all of the codes. This can cause confusion when trying to properly diagnose your automobile. A scan tool from Ross Tech would be a great investment in diagnosing your automobile accurately, and would also let you pull other information that is essential to the overall health of your automobile. A Malfunction Indicator Light (MIL) in the instrument cluster alerts the driver to the fault and the need to have the system checked for fault codes. These codes follow a standard format and are known as Diagnostic Trouble Codes (DTCs).
DTCs are assigned two codes. The first code is a numerical code assigned by the factory. The second code is referred to as a P-code and follows a structure required by law and defined by the Society of Automotive Engineers (SAE). This standard uses a letter to designate the system and four numbers to further identify and detail the malfunction as listed below.
Cables, Software, & Port Information
To read codes from your automobile, a few things will be needed and the ODB port will need to be located:
- Software:
- Cable(s):
- OBD Port:
Code Structure
- First digit structure is as follows:
- Pxxxx for powertrain
- Bxxxx for body
- Cxxxx for chassis
- Uxxxx for future systems
- Second digit structure is:
- P0xxx Government required codes
- P1xxx Manufacturer codes for additional emission system function; not required but reported to the government
- Third digit structure is:
- Px1xx measurement of air and fuel
- Px2xx measurement of air and fuel
- Px3xx ignition system
- Px4xx additional emission control
- Px5xx speed and idle regulation
- Px6xx computer and output signals
- Px7xx transmission
- Px8xx transmission
- Px9xx control modules, input and output signals
- The fourth and fifth digits designate the individual components and systems.
OBD1 vs OBD2
OBD1 (ECU code: xxx xxx 258)
Model years 92-95, through the July 95 build date. Early ECU's used socketed EPROMS, later cars had soldered in EPROMS. Early OBD1 cars (Passats and Corrados) had the scan plug underneath the shifter console and don't use an OBD2 compatible plug (the so known 2x2 black & white connectors). There is an adapter available that lets you use the VAG-COM software on these cars. OBD1 uses a normal plate style throttle body, and uses an external idle air control valve to control the idle. The TPS is removable and replaceable. OBD1 features only a primary oxygen sensor (O2) for closed loop fuel trim. The O2 loop is disregarded at WOT. OBD1 uses exhaust gas recirculation (EGR) to lower emissions and the minimum octane rating. There is a control solenoid, as well as a vacuum operated valve in the EGR system. Later cars use a smog pump to lower startup emissions. OBD1 computers only have minimal diagnostic functions and do not have datalogging capability on board. There are many OBD2 blocks that are not accessable on these ECUs. Intake manifold is drilled for the EGR, early Throttle Body, as well as the idle air control valve. Not interchangeable with OBD2 ones without major modification. Early production 92 cars have no check engine light, all others are equipped with one.
OBD2 (ECU code: xxx xxx 259)
Model years 96-present, from the August 95 build date onward. OBD2 cars feature the scan port in the dashboard for diagnostics, as well as a check engine light in all models. OBD2 uses a normal plate style throttle body, and uses an internal idle air control valve to control the idle. The TPS is not removable and replaceable. Idle adaptation can be done with the VAG-COM software. OBD2 features dual oxygen sensors (O2). The precat O2 is for closed loop fuel trim. The post cat O2 is used for emissions. The O2 loop is disregarded at WOT. OBD2 does not use exhaust gas recirculation (EGR). All cars use a smog pump to lower startup emissions. OBD2 computers only have full diagnostic functions and have datalogging capability on board. These codes can be scanned by a generic OBD2 reader, a VAG machine or the VAG-COM software package. There are many diagnostic blocks available. Intake manifold not drilled for EGR, or the idle air control valve. Not interchangeable with OBD1 ones without major modification.
Code Database
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