Flashing, or the car feels wrong? Stop somewhere safe
If the engine light flashes, or it comes on with shaking, a loss of power, smoke or a hot smell, pull over somewhere safe and switch off. Wikipedia's entry on the light describes a flashing one as a severe fault that makes the car unsafe to drive. On a motorway, AA New Zealand says to get as far left as you can, hazards on, and to stay belted in on the side away from traffic unless getting out is safer. If anyone is hurt or in danger, call 111.
What is the check engine light telling you?
The light is amber and usually shaped like an engine. It belongs to the engine management system. When a sensor reads something outside the range it expects, the computer stores a fault code and turns the light on.
That code could point at almost anything. Wikipedia's list runs from a loose fuel cap to a serious engine fault, and AA New Zealand adds that flat batteries, water in the wiring and a badly done jump start can upset the engine computer itself.
Each code is five characters. The first letter says which system logged it: P for the engine and gearbox (the powertrain), B for the body, C for the chassis and U for the network that links the car's computers.
Steady or flashing: what each one asks of you
| Steady light | Flashing light | |
|---|---|---|
| What it usually means | A fault stored that wants reading soon | A severe fault; Wikipedia calls it unsafe to drive |
| Driving | Gently, to a garage, if the car feels normal | Pull over safely and switch off |
| Next step | A code read and a test of the part it points to | Roadside help, a tow, or a mobile mechanic at the car |
What to do in the first few minutes
Notice what else changed
Is the car shaking, down on power, smelling hot, or showing a red light as well? Any of those moves it from 'soon' to 'stop now'.
Check the gauges
Temperature in its usual place and no red oil light? Then it's likely a job for the next few days rather than a tow.
Photograph the dash
Take a photo of every light that's lit, and the odometer. Lights can go out and come back, and a photo beats trying to remember.
Check the fuel cap
If you filled up just before it came on, make sure the cap clicked shut. Tighten it if it was loose, and still get the code read, because a loose cap is only one of many causes.
Write down when it happened
Cold start, motorway, uphill, after a fill? Put it in the note on the card so the mechanic knows where to start.
Is your car a Japanese import?
Plenty of New Zealand cars arrived second-hand from Japan, and many were built to JOBD, the version of the diagnostic standard for cars sold there. Mention it's an import when the mechanic rings, so they come with a scan tool that reads the car's own system and not just the generic codes.
European cars use EOBD, which shares the same plug and signals. Whatever the car, a code tells the mechanic where to start looking. It isn't a parts list.
What the mechanic will do
A good mechanic reads the stored codes and the freeze-frame data (a snapshot of what the engine was doing when the fault was logged). Then they test the part the code points to before replacing anything, because one code can have several causes.
Clearing the code without fixing the cause only hides it for a while. Wikipedia's entry on on-board diagnostics makes the point that resetting codes doesn't deal with the underlying issue. Ask for the code numbers and the test that confirmed the fault, in writing with the quote.
Will the engine light stop the car passing its WoF?
The WoF isn't an engine check. The MTA lists what's inspected (tyres, brakes, lights, steering and suspension, the exhaust and more) and says engine condition isn't part of it.
That's no reason to leave the light on until the inspection. If the fault behind it makes the exhaust smoky, the exhaust is on the list. Get the code read beforehand, and ask the inspector if you're unsure how they'll treat a warning light.
What you can do, and what's the mechanic's job
You can
- Photograph the dash and note the kilometres.
- Check the fuel cap is clicked shut.
- Check the oil level on a cold car parked on flat ground.
- Read the warning-light pages in the owner's manual.
Leave to the mechanic
- Reading the codes with a scan tool that suits the car, import or not.
- Testing sensors, ignition and fuel parts before replacing them.
- Clearing the code once the cause is fixed, then a road test to make sure it stays off.
If it were our car
A steady light on a car that drives normally: we'd get the codes read this week and ask for the result and the fix in writing. A flashing light: we'd stop, switch off, and have the car seen where it sits, by a mobile mechanic or after a tow.