Car electrical problems we trace most
- A battery that goes flat after the car sits for a day or two
- Power windows, locks or mirrors that work some days and not others
- Headlights or dash lights that flicker, or dim at idle
- A blower fan that only runs on high, which usually points to a failed resistor or a melted connector, covered with other cabin comfort faults under heating and A/C repair
- Several warning lights at once, such as ABS, traction control and airbag together
- Gauges that drop to zero while driving, or a radio that keeps resetting
- No crank at all, even though the battery tests fine
The battery that keeps going flat
When a car is switched off, its modules are supposed to go to sleep and draw only a tiny current, enough to keep the clock, the alarm and the keyless entry alive. If one circuit stays awake, it slowly empties the battery. Replacing the battery hides that for a while, then the new one goes flat as well.
To find a parasitic drain, we connect an ammeter into the battery circuit, lock the car, and wait for the modules to time out, which can take anywhere from a few minutes to the better part of an hour on newer vehicles. Then we measure the voltage drop across each fuse to see which circuit is still drawing current, without pulling fuses and waking everything back up. Typical finds are a glovebox or trunk light that stays lit, a module that never sleeps, a sticking relay, and aftermarket accessories. If the battery and alternator themselves are in doubt, those get tested first, as described on our battery, starter and alternator page.
Grounds, connectors and road salt
Every circuit needs a path back to the battery, and on most cars the body and engine block form part of that path. The ground straps between engine, body and battery corrode, especially where salt spray reaches them. A bad ground produces symptoms that seem unrelated to each other: dim lights, slow cranking, jumpy gauges, modules dropping off the network.
Ottawa winters are rough on wiring. Brine gets into connectors at the wheels, under the car and in the engine bay, and turns copper green inside the insulation where nobody can see it. Harnesses that flex every time a door opens, at the rubber boot between the door and the body, crack in the cold after enough years. We test with voltage drop measurements under load, because a wire can show perfect continuity on a meter and still fail to carry current the moment a motor asks for it.
Modules and network faults
A modern car runs on a network of control modules that share information over a pair of wires, usually called the CAN bus. When one module stops talking or the network wiring is damaged, a group of systems that seem unrelated can fail together, and the dash lights up like a slot machine. A scan shows which modules are not responding, and that tells us where on the network to start looking.
Sometimes a module really has failed. More often it has lost its power feed or its ground, or water has found its way into its connector. Where a module does need replacing, many have to be programmed or configured to the vehicle before they will work.
Remote starters and other add ons
Remote starters are close to standard equipment in Ottawa, and most are added after the car leaves the dealer. A tidy install is reliable. A rushed one with tapped wires, loose connections or a module that never sleeps is behind a lot of drains, intermittent no starts and odd security light problems. The same goes for aftermarket stereos, dash cams wired to constant power, and trailer wiring that has sat in slush for several winters. We check add ons early in the process, because they are a frequent source and quick to rule in or out.
What electrical diagnosis costs
Electrical diagnosis at our shop in Ottawa, ON starts at $150 before tax, parts extra, and the scan is included. That covers the testing to locate the fault. Once we know where it is, you get a price for the repair, whether that turns out to be a ground strap, a section of harness, a connector or a module.
Some electrical faults show themselves within minutes and others take patience, so describe the symptom in as much detail as you can when you book your appointment. Note whether it happens wet or dry, hot or cold, and what else is switched on at the time. If the same fault also turned on the check engine light, our car diagnostics page explains how those codes fit into the picture.
Questions
Why does my car battery keep dying overnight?
If the battery tests healthy and the alternator charges properly, something is drawing power after the car is shut off. Common causes are a module that never goes to sleep, a light that stays on, a sticking relay or an aftermarket accessory such as a remote starter. A parasitic drain test finds which circuit is responsible.
How do you find a parasitic battery drain?
A meter is connected in the battery circuit and the car is left locked until its modules go to sleep. The voltage drop across each fuse is then measured to see which circuit is still drawing current, without pulling fuses and waking the system up again.
How much does auto electrical repair cost in Ottawa?
At Scorpion Auto Tech on Blackwell Street in Ottawa, electrical diagnosis starts at $150 before tax, with the scan included. Once the fault is found, the repair is priced separately, since a corroded ground strap and a failed control module cost very different amounts.
Can road salt cause electrical problems in a car?
Yes. Salty slush works its way into connectors, ground points and wiring under the car and around the wheels, and corrosion spreads inside the insulation where it cannot be seen. That causes intermittent faults, warning lights and circuits that only fail when wet or cold.
Can a remote starter drain my car battery?
It can, especially if it was installed with poor connections or its module does not go to sleep properly. A remote starter is one of the first things worth checking when a car with a healthy battery keeps going flat, or shows security and immobilizer faults.
