www.automedicsafrica.com

What are the most common trouble codes that can cause your Check Engine light to come on and make your car or truck fail an OBD II plug-in emissions test? Of the vehicles tested, 6.3 percent ( a little over 100,000 vehicles) failed their initial test because of the presence of one or more trouble codes.

Most Common Trouble Codes

The following is the list of the 20 most common OBD II trouble codes with the percentage of failures.
P0420 - Catalyst System Low Efficiency - 13.2%
P0171 - Fuel Trim System Lean Bank 1 - 10.4%
P0401 - Exhaust Gas Recirculation (EGR) Flow Insufficient - 8.4%
P0174 - Fuel Trim System Lean Bank 2 - 6.8%
P0442 - Evaporative Emission (EVAP) System Small Leak Detected - 6.7%
P0300 - Engine Misfire Detected (random misfire) - 6.4%
P0455 - Evaporative Emission (EVAP) System Leak Detected (large) - 6.2%
P0440 - Evaporative Emission (EVAP) System - 5.5%
P0141 - Oxygen Sensor Heater (H02S) Performance Bank 1 Sensor 2 - 5.1%
P0430 - Catalyst System Low Efficiency Bank 2 - 3.2%
P0135 - Oxygen Sensor (HO2S) Performance Bank 1 Sensor 1 - 3.2%
P0446 - EVAP Vent Solenoid Valve Control System - 3.1%
P0128- Coolant Thermostat - 3.1%
P0301 - Cylinder 1 Misfire Detected - 3.1%
P0411 - EVAP System Control Incorrect Purge Flow - 2.8%
P0133 - Oxygen Sensor Slow Response Bank 1 Sensor 1 - 2.8%
P0303 - Cylinder 3 Misfire Detected - 2.6%
P0304 - Cylinder 4 Misfire Detected - 2.6%
P0302 - Cylinder 2 Misfire Detected - 2.6%
P0325 - PCM Knock Sensor Circuit - 2.1%

www.automedicsafrica.com
Based on the above data, it would seem likely that the number one most common reason for the Check Engine light coming on and failing an emissions test would be a worn out or fouled catalytic converter. But when you combine all of the related codes by system or component, you get a somewhat different picture. Looking at the data this way, these are the systems that are most likely to cause an emissions failure:
Evaporative Emission System - 24.3%
Engine Misfire - 17.3%
Fuel Trim (lean) - 17.2%
Catalytic converter - 16.4%
Oxygen sensor related - 11.1% Exhaust Gas Recirculation (EGR) system - 8.4%

Causes of Common Trouble Codes

To pass an OBD II plug-in emissions test, all of the OBD system monitors (self-tests) must have run and completed, and there must be no trouble codes found. So if your vehicle has one or more trouble codes, simply erasing the codes with a scan tool won't fix your problem. The cause of the trouble codes has to be diagnosed and repaired. The vehicle must then be driven until all of the OBD monitors complete their self-tests (which can be verified with a scan tool), and there must be no new codes. Then and only then will the vehicle pass the OBD II plug-in emissions test.

www.automedicsafrica.com

My Toyota Camry 2001 has the code P0401. Pls how do I get to rectify it. Thanks

Not sure of the code but the most common causal factor is not tightening your gas cap.