What the $50 scan covers
Computer scanning or diagnostics is $50 before tax at SA Auto Repair. A scan tool plugs into the OBD2 port under the dashboard, which every gas car and light truck from the late 1990s on has, and talks to the car’s computers. It reads the codes that turned on a light, and a fair amount more than that.
- Stored codes, the ones that lit the warning light.
- Pending codes, faults the computer has seen once but not yet confirmed.
- Freeze frame data, a snapshot of speed, engine temperature and load at the moment the fault was recorded.
- Live data from the sensors while the engine runs.
- Readiness monitors, which show whether the car’s self tests have finished since the codes were last cleared.
A code is a starting point, not a part number
Trouble codes name a system, not a broken part. Take P0171, system too lean. The computer is saying there is more air than it expected for the fuel going in. That can be a cracked intake hose letting in unmetered air, a dirty mass airflow sensor reading low, a weak fuel pump or a leaking injector. Four different repairs, one code.
This is why reading a code and buying the part named in its description so often goes wrong. A new oxygen sensor will not fix a vacuum leak, and the light comes back a week later. The diagnosis is the step between the code and the repair, and it is the step that saves money.
What diagnosis involves after the scan
Once the codes are read, the work is narrowing the list down. In practice that means a few things, in roughly this order.
- Reading the freeze frame. A fault that set at idle on a cold engine points somewhere different from one that set at 100 km/h on the 417.
- Looking at live data, such as fuel trims, coolant temperature and how the oxygen sensors are switching.
- Looking at the area the code points to. In Ottawa that turns up salt corroded connectors, vacuum hoses gone brittle in the cold, and wiring chewed by mice that spent the winter in the engine bay.
- Testing the suspect part, with a meter or by swapping it with an identical one to see if the fault follows.
- Clearing the codes and driving the car to confirm the fix held.
Some faults show themselves in minutes. Intermittent ones, the kind that only happen on a cold start or after a long drive, take longer. If finding the cause needs more than the scan, you are told what the next step involves before it starts.
Warning lights other than check engine
The check engine light is only one of the lights a scan can explain. ABS, traction control, airbag, tire pressure, transmission and charging system lights each come from their own module. A cheap code reader usually only talks to the engine computer, which is why someone may have told you there are no codes while your ABS light stays on.
A few are especially common here. ABS lights often trace back to a wheel speed sensor or its wiring corroded by salt. A battery or charging light on a cold morning sometimes points to the alternator, and sometimes to a battery that is simply worn out, which a load test sorts out on the battery replacement side. If it is the check engine light specifically, solid or flashing, the check engine light page covers what usually causes it.
Problems that do not set a code
Plenty of faults leave nothing in the computer. A vibration at highway speed, a hard start only below minus 20, a smell of coolant with the heat on, a stumble when the engine is cold. These are found by reproducing them, so details matter more than anything.
When you book, write down when it happens, how cold it was, how fast you were going, and how often. You can attach up to four photos. A picture of the dash with the lights on, or of the spot your car leaves on the driveway, is often more useful than a description. If the scan and testing point to a larger mechanical job, engine repair is quoted separately once the cause is clear.
Scanning a used car before you buy
A scan before a private sale costs less than most people spend on gas to go and see the car. Stored and pending codes tell you what the computer has been unhappy about. Readiness monitors that are not complete can mean the battery was disconnected or the codes were cleared shortly before you arrived, which is worth asking the seller about. Our longer write up on what a diagnostic scan tells you goes through the readings in more detail.
Booking a diagnostic in Ottawa, ON
Book online any time and choose computer scanning or diagnostics. Add the car by VIN or by year, make and model, describe the problem, and choose drop off if you cannot wait around. Last drop off is 2pm. We are at Unit 1, 1541 Star Top Road, a short way up from Innes Road at Highway 417 Exit 112, open weekdays until 6pm and Saturday until 2pm.
If the car will not drive, we do not tow. Arrange a tow to 1541 Star Top Road and call (613) 744-1521 first so we know it is coming.
Questions people ask
How much does a car diagnostic cost in Ottawa?
At SA Auto Repair on Star Top Road, an OBD computer scan and diagnosis is $50 before tax. The scan reads stored and pending codes, freeze frame data and live sensor readings, and you get an explanation of what they point to.
Is a code reading at a parts store the same as a diagnostic?
No. A basic code reader gives you a code number, which names the system the computer was unhappy with, not the part that failed. A diagnostic looks at the data behind the code and checks the likely causes, so you do not end up buying a sensor the car never needed.
Will clearing the code fix my car?
No. Clearing a code only turns the light off. If the fault is still there, the computer sets the code again, sometimes within a single drive. Clearing codes also resets the readiness monitors, which shows up on the next scan.
Should I get a scan before buying a used car in Ottawa?
It is a cheap check before a private sale. A scan shows stored and pending codes, and readiness monitors that are not complete can mean the battery was disconnected or the codes were cleared shortly before you arrived.
What if my car has a problem but no warning light?
Not every fault sets a code. Noises, vibrations, smells and problems that only happen in deep cold are found by reproducing them, so the more detail you give about when it happens, the faster it goes.
