NANO

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.