From car hell to a working system
My daughter's 2011 Vauxhall Astra started cutting out for no obvious reason back in November last year. No warning, no pattern, just dead and sometimes at the worst possible moment in traffic or stood at traffic lights with a long tail of cars behind.
I'm reasonably handy with cars so I decided I'd have a look at it to see what I could see.
The spiral begins
First thing is the car was struggling to crank so I swapped in a new battery. Better crank but same problem, it was still randomly cutting out. It was December and while it was in for its MOT I asked the garage to take a look to see if they could see the problem. They fitted a new crank sensor. They said they'd fitted a non-branded part, suggested that if it didn't work it could be an ECU problem, "See how you go."
It didn't go and the problem persisted, their advice was get rid and buy a different car.
Two months in I'd had to rescue my daughter from the roadside a fair few times. She gave up on the car and switched to public transport and I took the car to mine and started to try and diagnose it myself.
A parts lottery
OBD codes were pointing at cam timing so I worked through the most likely causes in order:
New coil pack - branded part
New throttle body - branded part
New cam actuators x2 - branded part
None of it helped but now I had the car on my driveway and I could at least experience the fault first-hand. The cut-outs were more likely when the car was up to temperature, both intake and exhaust cam sensor codes would often present together which made the sensors themselves unlikely culprits because you don't usually get both failing simultaneously.
I called out a mobile mechanic with a better scanner (Autel) for a second opinion. His verdict: timing chain and to be fair it correlated with the codes and the age and mileage on the car. He said it wasn't a job he could do and it needed a garage.
£820 and a week in a specialist workshop
I ruled out doing the timing chain myself, no workshop, lack of timing locking tools and the top off the engine on the driveway in winter didn't appeal. So I found a Vauxhall specialist, these guys do Vauxhalls all day every day so if anyone could crack this tricky intermittent fault it would be them.
They quoted £820 including VAT if the timing chain needed doing, they removed the valve cover and showed me a video of slack in the chain. At 78K miles and the age of the car it was in the zone so I told them to do it.
A week later, we picked the car up and it cut out on the drive home from the garage :)
The long tail
Back it went and over the next few weeks they found a failing ambient air temperature sensor on a test drive. Unlikely to be the cause but a fault is a fault and they changed it and didn't charge for labour, £45 for the part. See how you go. It failed again two days later.
Back in. Radio silence for a few weeks while they try and fit it around other jobs. Then a call "We think it might be the ECU." An ECU specialist was brought in but they don't test ECUs, they pull the data from the old one and flash it to a fresh unit then hand it back for in-car testing. Another couple of weeks and another few hundred pounds.
The fresh ECU ruled it out, the ECU was fine and the problem was still there.
At this point a light bulb must have come on with the Vauxhall specialist guy working on it after he'd seen the ECU was fine
The answer was there from the start
The tech had by now experienced the fault himself and was confident: crank sensor. The first thing that had been replaced months ago. But he was able to explain what nobody had mentioned before: a failing crank sensor can fail in both states of high 12v and low 0v and when that happens it explains the symptoms we'd experienced. Intermittent cutting out, intermittent no-crank on the key, temperature heat soak correlation, all of it.
The original garage had fitted a non-branded part and the new guys replaced it with a quality branded sensor. The didn't charge for labour again which was great, £50 for the part. "I'm 99% certain that it's fixed."
It was fixed and the car's been running fine since.
Six months, hundreds in parts, £820 for a timing chain that wasn't the issue, a replaced ECU that didn't need replacing and the fix was a £50 branded crank sensor, the same part changed on day one done wrong.
The original garage had even flagged the risk of the non-branded part and it just got lost in the noise.
During all of this trauma I had the idea that if there was a platform where someone had documented something like: "2011 Astra, cutting out, cam/timing DTCs presenting together, intermittent no-crank when hot, check the crank sensor, fit a branded part" then maybe we'd have been done in a week.
This is why I built FaultNet
Structured searchable fault intelligence, real symptoms, real DTC codes, real resolutions not buried in forum threads you have to trawl through at midnight hoping someone has had the same problem. A place where this exact fault with this exact fix can live in a structured record that the next person can actually find.
I suppose the moral of this story is not that garages are incompetent. Most of the people who worked on this car myself included were doing their best with intermittent hard-to-reproduce symptoms. The moral is that the knowledge existed somewhere and it just wasn't findable. Someone, somewhere had already solved this and we had no way to know that.
FaultNet is my attempt to fix this problem.
FaultNet is live at faultnet.io - structured fault cases, DTC lookup, pattern discovery across vehicles, AI analysis. Currently in beta with an Android app coming soon. If you've ever stared at an OBD reader wondering what to do next it's for you.
