Leno: Troubleshooting modern supercars is tricky, but rewarding
Does anyone remember the Plymouth Trouble Shooting Contest? It started in the 1960s and ran for a couple of decades. They used to line up dozens of new Plymouths with some problem that was really hard to diagnose, from a bad ballast resistor to tape hidden on the battery post, and high school kids from all over the country competed to figure out the problem. There were local, regional, and national levels, and thousands of kids were in it. I was thinking of that the other day, because cars back then were much harder to diagnose but much easier to fix compared to today’s cars, which have onboard diagnostics to tell you what’s wrong, but can be challenging to fix unless you’re persistent. I’ll give you two recent examples from cars here at the garage.
The battery in the 2005 Ford GT was dying, so I bought a new one. At the same time, a friend needed a battery for his BMW and the dealer quoted $600 for the job. He told the dealer forget it, he would do it himself, but the service writer said if he doesn’t keep the car connected to power at all times while changing the battery, the computer loses its memory and goes haywire, so my friend just paid the money. Well, figuring the GT is just a Ford, like an idiot I simply disconnected the battery and dropped in the new one. And bink! All the dash lights came on and every trouble code came up.
I tried to turn off each one, in the process discovering that the thermostat had just enough crud on the edge that it was stuck open, such that the engine temperature wasn’t fully coming up. After fixing that, I still couldn’t get the codes to clear, so I called Ford. They told me about something called the “drive cycle,” in which you drive for a specific distance and at specific speeds, and the computer clears the codes itself. I ran two full tanks of gas through the car, but I still couldn’t get the codes cleared. So I called Ford back and this time I got a different guy who explained that you have to run the drive cycle exactly, meaning: idle vehicle for exactly 15 seconds; drive at exactly 40 mph until the temperature is at least 170 degrees; cruise at 45 to 65 mph for 10 minutes avoiding sharp turns and hills; from a stop, accelerate to 45 mph at one-half to three-quarter throttle, repeat three times—and on and on. I did that, and bink! The codes cleared. It was unbelievable. All I did was something that nobody ever does, which is follow the directions, and it worked perfectly. But only if you know the secret.
Another example is the Mercedes-Benz SLR McLaren, which lit its check-engine light just as I was going in for a smog test. I didn’t want to call the dealer right away because you know that’s going to be expensive, so I plugged in my little $30 scan tool and got a P0442 code, which is a leak in the evaporative emissions system. That’s the code where they always tell you to check your gas cap first. Mine was tight, so I figured that maybe it was a dried-out filler-tube gasket, because the car sits a lot. So I and the guys here started to take the car apart. The gasket looked brand-new, no seeping, no wetness, no nothing, and that was scary, because it wasn’t clear where we should go from there.
Not knowing any better, I started tracing the fuel lines and eventually came to a plastic T-fitting that on close inspection showed just a small hairline crack in it. Wondering if that was a problem, I touched it and it literally fell apart in my hand. Since it was plastic and 15 years old, I decided it was better to replace it with a brass fitting. When we did and started the car up, the check-engine light went out.
It was amazing! For 30 bucks, I fixed an SLR McLaren. It gave me such a degree of satisfaction that I drove the car every day for the next week, because I felt like I’m not just some rich sod who drives around in fancy cars—I actually fixed mine and got it to work. Now I tell people that if their expensive new car is showing a check-engine light, it’s probably something really simple. Just don’t bring it to me. I’ve got enough of my own cars to fix.