Tina sent the text at 7:42 on a Tuesday morning: "Orange engine light. Van seems fine. Do I keep driving?" She had filled up the night before at the Hy-Vee on the way home from the flower shop, and the Sienna was sitting at about 188,000 miles, so my first thought was not a happy one.
I asked one question back: is it steady or flashing? Steady. That was the answer I wanted. A flashing check engine light usually means a misfire bad enough to cook the catalytic converter, and that's a pull-over-and-call-someone situation. A steady light means the computer has seen something it doesn't like and wrote it down. I told her to drive to work like normal and I'd look at it after my shift.
The free scan
Most of the auto parts stores in St. Joseph will read your codes for free. You pull up, a guy walks out with a handheld scanner, plugs it into the port under the dash by your left knee and reads off what the computer stored. It takes about five minutes.
The van had one code, P0455, which the scanner described as an evaporative emission system leak, large. The EVAP system is the plumbing that catches gas fumes from the tank and feeds them back to the engine to burn instead of letting them drift into the air. The computer tests it now and then by sealing it up and checking whether it holds pressure. If it doesn't, you get a code.
The counter guy said what I was already thinking: "Check your gas cap first." On a car that just got filled up, a loose or worn cap is the most common reason for that code by a long way. It can also be a cracked hose, a bad purge valve or a leaking charcoal canister, and those cost real money. The cap is where you start because it's cheap and it takes ten seconds.
What the cap looked like
I took the Sienna's cap off in the parts store lot and looked at the rubber seal on the underside. It had a crack running about a third of the way around and the rubber was hard, like an old pencil eraser. The cap was very likely original to the van, which means it had been clicked on and off something like two thousand times. Tina admitted she sometimes gives it "one click, maybe."
A new cap was $19 for one built to the Toyota spec. I put it on until it clicked three times, which is overkill but makes me feel better. The counter guy offered to clear the code with his scanner. I said no, and here's why: if you clear it right away and the light comes back, you've learned something, but if you let the van's own tests run and the light goes out by itself, you know the fix worked. On most cars the computer needs a few days of normal driving to rerun the EVAP test, and the light clears itself if the leak is gone.
It took three days. Thursday evening Tina reported the light was off. A scan on Saturday showed no stored codes.
What it would have cost otherwise
Our shop on the south side, which I trust, charges a flat $150 for check engine diagnostics. They hook up a better scanner than the free one, and if the cap checks out they can run a smoke test, where they push visible smoke into the EVAP system and look for where it leaks out. If it had been a hose or a valve, that $150 would have been money well spent.
But for a $19 cap, I'd have paid them $150 to tell me what the parts store told me for nothing. That's the arithmetic I keep coming back to. The free scan doesn't fix anything, but it tells you which question to ask next.
Here's the order I'm going to follow from now on when the light comes on:
- Steady or flashing? Flashing means slow down, get off the road and call a shop.
- If it drives normally, get the code read for free that day or the next.
- Look up the code and try the cheap, likely fix first if there is one.
- Let the car clear the light on its own before calling it done.
- If the light comes back, that's when the shop gets the $150.
The same week, I bought my own code reader for $38. It's a basic plug-in model that reads and clears codes and shows whether the emissions monitors have finished their tests. It lives in the Silverado's glove box now. If it saves one trip to the parts store or one diagnostic fee over the next five years, it paid for itself twice.
I wrote the whole thing in the mileage notebook: date, mileage, code, $19 cap. Tina said it was the most excited she's ever seen me about a piece of plastic. That's probably fair. The van is 14 years old and most of what it's going to need from here costs a lot more than nineteen dollars, so I'll take the cheap wins when they show up.