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 Explaining Automotive Trouble Codes - What your Scan Tool is Saying.

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shatto

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PostSubject: Explaining Automotive Trouble Codes - What your Scan Tool is Saying.   October 8th 2013, 7:20 pm

Brad Bergholdt, McClatchy-Tribune News Service

QUESTION: I just bought a scanner to check my car. Can you explain how the codes work?
--Nick Dunton

ANSWER: Your new scan tool provides a great learning opportunity and will make you quite popular with family and friends. I'll assume this is a consumer-friendly OBD-II generic scan tool, which typically costs $50-$150 and provides a helpful glimpse of engine and transmission systems. OBD-II is a government-mandated on-board diagnostic system that provides standardized monitoring and testing procedures related to emission control compliance. In other words, if an engine or transmission fault occurs that can cause exhaust emissions to rise unacceptably, the "check engine" light will be illuminated and a diagnostic trouble code, or DTC, will be recorded.

We need to keep in mind that the many faults unrelated to emissions that can develop in the engine, transmission, body, brakes and other systems, but will not illuminate the light or provide OBD-II scan tool visibility. OBD-II is very useful, but is only the tip of the vehicle diagnostic iceberg. A much more costly professional grade scan tool is needed to view and test other codes and systems.

OBD-II DTCs consist of five alphanumeric digits. Let's use P0118 as an example: P indicates this is a powertrain (engine or transmission) code, the only kind you'll see on an OBD-II scan tool. Other letters, typically requiring a higher end tool are B (body), C (chassis, brakes), and U (network). The second digit: 0 (may also be a 2) indicates this is an OBD-II generic code. If a 1 or 3 appears here this means the code is a manufacturer-specific (enhanced) code. These occur when a component or system is unique to a car brand or falls outside standardization. The third digit (1 in this case) indicates the sub system. 1 is emission management, 3 is ignition system or misfire, 7 is transmission. Other numbers between 1-7 require more lengthy explanation. The fourth and fifth digits (18) indicate a particular problem. In this case we have an abnormally high voltage in the engine coolant temperature sensor circuit, a fault that could affect all vehicles similarly.

P0118 can be caused by a poor connection in the sensor circuit wiring/connectors, a faulty sensor or, in very rare cases, a faulty powertrain control module. Throwing parts at a car because a certain DTC occurs doesn't work very well. It's best to obtain the manufacturer's recommended diagnostic procedure for that DTC and follow it, to avoid unnecessary parts replacement or labor. Also, the fault needs to be presently occurring for the procedure to be valid.

In addition to being able to retrieve and clear DTCs, your scan tool provides a snapshot or freeze frame of vehicle operating conditions when a DTC sets. This is helpful when diagnosing faults or validating repair success. Parameter identification data allows almost a real-time view of important -- but not all -- sensor readings and fuel trims, or correction values. A check of monitor status, via tests that the OBD-II system runs on components and systems, confirms whether the vehicle is happy with a previous repair or is ready for an emission test. Additional diagnostic information may also be available, depending on the scan tool's capabilities.

About The Writer

Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, Calif. Readers may send him email at under-the-hood@earthlink.net; he cannot make personal replies.

Read more at http://www.arcamax.com/business/businessnews/s-1397130#XZd7z74MfM4hSZWV.99
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TheQuig

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PostSubject: Re: Explaining Automotive Trouble Codes - What your Scan Tool is Saying.   October 10th 2013, 7:30 pm

I bought an inexpensive OBDII off Amazon when my wife had a code pop up on her Yukon. $18. It came with a book, and CD. As it turns off she was out of state where you guys have to pump your own gas. She didn't put the gas cap on tight and it pulled up a check engine code. Auto Zone wouldn't reset it and I didn't want to wait for a certain amount of starts to erase the code so I pulled the battery cable for 15 minutes and it reset.

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Don't believe everything you read on the internet- George Washington.
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shatto

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PostSubject: Re: Explaining Automotive Trouble Codes - What your Scan Tool is Saying.   October 10th 2013, 7:50 pm

I had a similar problem with a borrowed 'Q' when the big screen in the dash screamed that the world was coming to an end. The dealer just smiled and tightened the cap a few clicks.
It was tightened the way I did my Dakota tank for half a million miles with no trouble so I dodn't know better.
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