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28/04/2014

Repair Car with Misunderstanding of OBD2 Diagnostic Tools

Many people might have confusion about obd2 diagnostic tools functions. Why obd2 tools cannot read out fault codes when some vehicles have issues. Actually, many people have a misunderstanding of obd2 diagnostic tools would figure out fault codes when vehicles have faults. 

 

Here I am taking GM Chevrolet sedan, release accelerator pedal, but when the car engine severely shakes for example.

 

Vehicle fault symptom: while riding a Chevrolet sedan, slow down suddenly after speeding up, engine severely shakes; shakes disappear after about 30 seconds.

 

Analysis and inspection: More severe problem when engine is cold. 

 

Connect obd2 scanner with vehicle, and found no faults codes. Check engine sensors and actuators, but still found no significant abnormalities; measuring the fuel system pressure, normal. After cleaning fuel injectors and idling motor, test but the failure phenomenon still exists. 

 

After heat each cylinder, and carry out engine cylinder pressure measurements and found that the first low pressure cylinder is lower than normal value; the rest cylinders are normal; measuring cylinder pressure of each cylinder when cooler, found the first cylinder pressure is substantially zero. Hence, open the intake valve chamber cover inspection, found the bottom of the first cylinder intake valve springs, resulting in the release of the accelerator pedal valve spring oscillation, causing the valve to close lax. When idling, the spring has a certain elasticity to meet the requirements of the valve opening and closing, thus operate stably; cooler but not yet built the main oil pressure, so the failure phenomenon is more obvious.

 

Troubleshoot: replacement of throttle springs

 

From this repair case, we know that not every car faults codes could be figured out by obd2 scanners. And what is more, obd2 scanners could figure out fault codes, it is a hint for your repairs, for complicated vehicle component structure, faults reasons are various; therefore, being paid attention to combine vehicle symptoms and faults codes read by obd2 tools together. In this way, you could have better understand obd2 tool functions and do better in auto repairs work. 

 

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