304 ENGINE 273 MPFI 3.11.5 TROUBLE SHOOTING AND DIAGNOSIS REPAIRING STEPS Use the DTC codes in conjunction with the vehicle’s service manual to ascertain which systems, circuits or components should be checked or tested for the correct diagnosis of the fault. It is advised that the parts or components should not be replaced only with reference to a DTC alone. If it seems that the fault can not be healed even after ensuring the good connections and no short circuits, it is recommended to check Component Fitment Data (3.11.4) before any replacement. The vehicle service manual should be consulted for more information on possible causes of the fault, along with required testing. For example, if a DTC reports a sensor fault, note that replacement of the sensor may not be the solution alone. It may not resolve the underlying problem. The root cause for the fault may be by the systems that the sensor is monitoring or but might even be caused by the wiring harness connecting the sensor and the ECU. The sequential repair steps to be followed during diagnostics of any mechatronic components are: • Check the wiring for any open circuit or intermittent faults. • Check the wiring for short circuits (short to Battery / ground) • Check the Component for damages/ failures • Check the ECU for possible faults. DTC’s may also be triggered by faults earlier down the line. For example, a dirty TMAP sensor might be causing the car to overcompensate in its fuel-trim adjustments. As a result, oxygen sensors are likely to report fuel mixture problems. After any repairing steps, erase all failures. Execute a driving cycle where you can bring together all conditions to allow detection and check the failure with a diagnosis tool. If the failure remains, check the next repairing step to remove it. Erasing fault codes from ECU: To erase all recorded faults following method to be followed: Ignition key ON and within 15 seconds press the accelerator pedal from 30 % to 80% at least 8 times wait for 10 seconds in key ON condition. Limitations of Diagnostic Tool: 1) Ignition Coil connections getting swapped or reversed , cannot be diagnosed. Check for ignition coil connector Poka-Yoke. 2) If the vehicle ignition switch is faulty Diagnostic Tool doesn’t record any fault codes. 3) The diagnostic tool cannot diagnose failures of relay-controlled actuators. The diagnostic tool can only diagnose actuating signals up to relay. Beyond Relay, Wiring and Actuator (i.e. Radiator Fan, AC Fan, AC Compressor, Fuel Pump) to be manually checked. 4) Failure of direct drive Components i.e. Stepper Motor, Canister Purge Valve, Ignition Coil, High Tension Lead, Spark Plug and Injector cannot be detected in diagnostic tool. 5) Internal Control Module Read Only Memory (ROM) Error cannot be diagnosed by ECU. 6) Below 6V, ECU stops functioning and can not diagnose anything. This usually happens during cranking with low state of charge battery.
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