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

Mazda CX-5 review - a sleek, left-field family SUV
2022 Mazda CX-5
In-depth reviews
12 Feb 2024

Mazda CX-5 review - a sleek, left-field family SUV

Top 10 most reliable cars 2024
The most reliable cars header
Best cars
2 Jan 2024

Top 10 most reliable cars 2024

Cheap fun cars: our picks from £1,000 to £10,000
Cheap fun used cars
Tips and advice
27 Jul 2023

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

Mazda6 saloon (2013-2022) review
Mazda6 driving
In-depth reviews
24 Mar 2023

Mazda6 saloon (2013-2022) review

Most Popular

Hot car deal: racy Cupra Ateca SUV for just £234 a month
cupra ateca
Deals
16 Feb 2024

Hot car deal: racy Cupra Ateca SUV for just £234 a month

Hot car deal: sporty Skoda Octavia vRS Estate for £278 a month
octavia vrs hot deal
Deals
19 Feb 2024

Hot car deal: sporty Skoda Octavia vRS Estate for £278 a month

All-new KGM Torres is a £35k SUV from reborn SsangYong
KGM Torres front quarter
News
19 Feb 2024

All-new KGM Torres is a £35k SUV from reborn SsangYong

Tips & advice

View All
Car dashboard warning lights: the complete guide
Car dashboard symbols and meanings
Tips and advice
19 Dec 2023

Car dashboard warning lights: the complete guide

Electric car charging stations: a complete guide
Public EV charge point
Tips and advice
11 Jan 2023

Electric car charging stations: a complete guide

PCP vs HP – which type of car finance is right for you?
PCP vs HP
Tips and advice
17 May 2022

PCP vs HP – which type of car finance is right for you?

Average speed cameras: how do they work?
Average speed cameras: how do they work?
Tips and advice
12 Apr 2023

Average speed cameras: how do they work?

Best cars

View All
Top 10 best car interiors
Peugeot 208 hatchback
Best cars
25 Jun 2021

Top 10 best car interiors

Top 10 best electric cars 2024
The best electric cars 2023
Best cars
2 Jan 2024

Top 10 best electric cars 2024

Top 10 best cheap-to-run cars 2024
The best cheap-to-run cars 2023
Best cars
2 Jan 2024

Top 10 best cheap-to-run cars 2024

The UK's top 10 fastest hot hatchbacks 2024
Fastest hot hatchbacks hero
Best cars
2 Jan 2024

The UK's top 10 fastest hot hatchbacks 2024