Watchdog: Driver baffled by intermittent stop/start

Mazda owner believes system is faulty but dealer and manufacturer don't agree

Stop/start is a piece of emissions-busting tech designed to kick in only when it’s beneficial. As you pull up to a set of lights, for example, the system makes a split-second decision about whether switching off the engine – then on again as the lights change – will use more energy than just leaving it running.

So how can you tell if the setup’s working properly? That’s the question frustrating Les Stone, of Salford, Gtr Manchester, who argues the i-stop system in his 62-reg Mazda CX-5 is suspiciously intermittent. Yet after repeated trips to RRG Mazda in Manchester, the dealer concluded there was no fault with the SUV’s stop/start.

Les told Carbuyer's sister site, Auto Express: “My dealer explained that anything which drained the battery, like the heated rear screen or the air-con, would affect whether it worked. Yet I noticed it would work first thing in the morning from cold, with everything switched on, but then not after a drive on the motorway. It didn’t make sense.”

We called Mazda for help, but it also argued Les’s i-stop wasn’t necessarily faulty. A spokesman said: “Myriad factors based on electrical loadings influence whether the i-stop works. It’s incredibly complicated. Ambient temperature will have an impact, for example, or even switching the cabin air flow from the windscreen to your face.”

The same journey, made on two different days, might therefore result in entirely different pattens of stop/start operation, the spokesman argued, adding: “If it hasn’t kicked in, it’s for a good reason. If it was faulty, there would have been a warning light and it would have been picked up by the dealer during diagnostic tests.”

If Les is still unconvinced, the consumer desk at Auto Express suggested he asks his dealer to make another CX-5 available for an extended test drive. He can then at least establish if the same intermittent pattern applies.

What should you do if it happens to you?

Comparing your car to an identical new model is a great way to test dealer claims there’s nothing wrong with yours. If you find it performs the same, you can assume it is a ‘characteristic’. If your garage refuses to offer a comparison test, however, we’d advise escalating the complaint to the manufacturer.

Recommended

2021 Mazda CX-5 gets new petrol engine and Kuro special edition
Mazda CX-5 Kuro
Mazda CX-5
26 Jan 2021

2021 Mazda CX-5 gets new petrol engine and Kuro special edition

Cheap fun cars: our picks from £1,000 to £10,000
Honda Civic Type R front
Toyota
5 Jan 2021

Cheap fun cars: our picks from £1,000 to £10,000

New Mazda MX-30 electric SUV: full prices and specs released
Mazda MX-30
Mazda
28 Sep 2020

New Mazda MX-30 electric SUV: full prices and specs released

100th Anniversary editions of Mazda MX-5, CX-30 and Mazda3
Mazda MX-5 100th Anniversary and Mazda R360
Mazda
3 Aug 2020

100th Anniversary editions of Mazda MX-5, CX-30 and Mazda3

Most Popular

What are Audi TFSI petrol engines?
Yellow Audi Q2
Audi
16 Apr 2021

What are Audi TFSI petrol engines?

Car dashboard warning lights: the complete guide
Car dashboard symbols and meanings
Tips and advice
13 Apr 2021

Car dashboard warning lights: the complete guide

Best new car deals 2021
Skoda Fabia
Deals
16 Apr 2021

Best new car deals 2021

Tips & advice

View All
Car dashboard warning lights: the complete guide
Car dashboard symbols and meanings
Tips and advice
13 Apr 2021

Car dashboard warning lights: the complete guide

Electric car charging stations: a complete guide
Tips and advice
10 Nov 2020

Electric car charging stations: a complete guide

PCP vs HP – what's the difference?
Tips and Advice
23 Mar 2020

PCP vs HP – what's the difference?

Average speed cameras: how do they work?
Average speed cameras: how do they work?
Tips and advice
24 Feb 2021

Average speed cameras: how do they work?

Best cars

View All
Best car interiors
Best cars
10 Mar 2020

Best car interiors

Best electric cars
Best cars
24 Dec 2020

Best electric cars

Best cheap-to-run cars
Toyota Prius front 3/4 cornering
Best cars
1 Feb 2021

Best cheap-to-run cars

The UK's top 10 fastest hot hatchbacks
Hot hatches
9 Apr 2020

The UK's top 10 fastest hot hatchbacks