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Matt, Mechanical Engineer
Category: Ford
Satisfied Customers: 22907
Experience:  BEng hons Mech engineering, in auto industry 22 years
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Car: Ford Fiesta 3 door Hatch batch 1.1 L reg: My engine

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Car: Ford Fiesta 3 door Hatch batch 1.1 L reg:

My engine warning light has come on and stays on all the time while I am driving. The engine appears to be labouring and when the car is stationery the engine sounds 'lumpy' when the accelerator is depressed. What is the possible cause and is the car safe to drive in its present condition?

On any car if you get a check engine light or other fault light this typically means one or more of the sensors has failed or has a faulty connection.

The ECU senses this and may put the car into 'limp home' mode which typically limits the revs and the amount of power available. Usually the car is safe to drive for a short distance as the mode is intended is intended to get you home without incurring any engine damage

The quickest route to repair is to have the car plugged into a diagnostic machine which will read off the fault code stored in the ECU (providing the light is still on at this point) and indicate which sensor has failed or whether the fault is more serious.

You can do a very rough and ready check yourself by unplugging sensors one at a time and seeing if any of them change the driving condition which would indicate the most recently unplugged sensor is the faulty one. This method is not foolproof though and reading a fault code off is the better method.

from your description though I'd say that this could be an issue either with the oxygen sensor in the exhaust or the MAF ( mass airflow meter)

so it would be worth checking the wiring and connector to the airflow meter for any signs of corrosion or damage. you can do a quick fault find if you unplug the meter and run the engine without it.
if the engine condition is the same then chances are the meter or the connection to it is faulty

its also worth cleaning the airflow meter by removing it from the car and spraying the exposed sensor wires inside the tube with a brake or switch cleaner - ensure that the cleaner is one of the old fashioned, non Eco type that does not leave a residue

On no account touch the sensor wires with anything physical as they are extremely fragile
Customer: replied 4 years ago.

Thankyou for your comprehensive imput. If the car is plugged into a diagonistic machine and the problem is found to be a sensor fault, how expensive is this likely to be to put right?


Also this may seem to be totally unrelated but is there a possibility that the problem could be caused by worn out spark plugs?

Hello Helen

a faulty sensor can be as little as £20 to repair or as much as £300, I'm afraid without more information I can' t make an accurate diagnosis

faulty plugs can produce a misfire which then will then produce a check engine light so it is a possibility

but really the next step is a diagnostic check as this will save you money by giving a quick an accurate diagnosis

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