Ask the Expert: Why doesn’t my Hyundai start when it’s warm?

Our reader is experiencing issues with their Hyundai i10
Our reader is experiencing issues with their Hyundai i10 - getty

Dear Alex,

My nine-year-old Hyundai i10 has always started first time, but recently it has occasionally failed to restart after a run of a few miles. The engine cranks but doesn’t fire.

If left for half an hour, starts fine. The AA replaced the original battery but the fault persists. No warning lights appear, and no fault was found on diagnostic check. The Hyundai dealer is unaware of similar problems and seems reluctant to attempt to fix the fault until it becomes permanent, as the cost of changing sensors would be prohibitive. Any ideas?

– SH

Dear SH,

It’s tricky to diagnose something that isn’t happening whenever it’s presented to a mechanic.

My money would be on a coolant temperature sensor. When this sensor fails, it can feed erroneous information about the coolant temperature back to the ECU [electronic control unit], which can then cause it to calculate the wrong fuel-air ratio. That can prevent the car from starting. Of course, the ECU doesn’t know there’s a fault when this happens, because it can’t tell, so no warning lights pop up, and no fault codes are recorded.

That said, there’s a wide range of alternative culprits. You could have a fuel pump that’s on its way out, or an electrical connection somewhere in the engine that’s expanding when it’s warm, preventing it from forming a good contact.

That’s probably why the dealer is cautious – especially if it’s tried to reproduce the fault and not been able to. And it has a point – you could spend a lot of money replacing bits and bobs to try to get to the bottom of the problem.

If I were in your shoes, I’d probably take the car to a good local independent garage to get a second opinion. They’ll be more cost-effective for sorting a problem like this, which might require multiple visits, and it sounds like they’ll have no less of a clue as to its cause than the Hyundai mechanics.

What’s more, they may have some advice gleaned from working on a panoply of different models. And they might be willing to replace the coolant temperature sensor at a more reasonable price than the main dealer, which might be worth a shot given it’s the most likely cause. Even if it doesn’t solve your problem, at least you will have eliminated it from contention.

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