Exhaust Leak Symptoms: Ticking, Rattles, Fumes and When It's a Safety Problem

An exhaust leak often shows up first as a noise, but the bigger concern is carbon monoxide (CO). Engine exhaust contains it, you can't see or smell it, and a leak can let it into the cabin. So any of the signs below is a reason to have the exhaust inspected, and some of them are a reason to stop using the car right away.

Which symptoms can wait for an appointment and which can't

Why an exhaust leak is a carbon monoxide risk

Health Canada lists vehicle exhaust among the sources of carbon monoxide and says a CO alarm is the only way to detect it.

The exhaust system carries exhaust gases from the engine to the tailpipe and out behind the car. A hole or a leaking joint anywhere along the way lets them out underneath instead, where they can find a way in. The U.S. Centers for Disease Control and Prevention (CDC) warns that a small leak in the exhaust system can lead to a buildup of CO inside the car.

ICBC makes the same point for BC drivers. Its Learn to Drive Smart guide puts checking the exhaust system on its winter preparation list, and warns that any leak can be extremely dangerous because CO can collect in a car when the windows and vents are closed.

If anyone in the car feels unwell

HealthLink BC lists tiredness, headaches, nausea, flu-like symptoms, dizziness, impaired vision and confusion as effects of CO exposure. Fraser Health adds shortness of breath, chest pain and vomiting, and notes that the symptoms can mimic the flu, without the fever.

Winter, snow and garages

Carbon monoxide can build up in a car even when the exhaust has no leak. Watch for these situations, especially in winter.

• Snow over the tailpipe. The CDC warns that if the tailpipe is blocked, for example by snow, CO can build up quickly inside the vehicle. Check that it's clear before starting the car after a snowfall.
• Stuck in snow. If you're stranded and running the engine for heat, ICBC's advice is to run it only about five minutes every hour, check that the exhaust pipe and system aren't blocked or damaged, keep one window slightly open, and make sure at least one person stays awake. Heading over the Coquihalla or through the Fraser Canyon? Work through a winter vehicle check for BC mountain highways before you go, kit list included.
• Warming up in the garage. HealthLink BC says never to idle a vehicle in an attached garage, and the CDC says that applies even with the garage door open. That includes a remote start on a cold morning.
• An open tailgate or hatch. If you're hauling something long with the hatch up, open the vents or windows too. The CDC warns that with only the tailgate open, CO from the exhaust is pulled into the vehicle.

What the noises usually mean

The timing of a noise and where it seems to come from can narrow things down, but only an inspection of the system confirms a leak.

Ticking or puffing on a cold start

The exhaust manifold is the heavy part bolted to the engine that collects exhaust from each cylinder. Brake & Front End, a trade magazine for technicians, notes that most manifolds fail at high-stress spots, where the flange meets the cylinder head or where its separate passages merge. A crack there, a failed gasket, or a loose or broken bolt lets each exhaust pulse escape through the gap, and you hear it as a tick, pop or puff that keeps time with the engine.

These leaks are often loudest right after a cold start. A 2023 manufacturer service bulletin for some Ram, Dodge and Jeep models with the 5.7 L Hemi V8 describes that complaint: a ticking noise from the exhaust manifold area when the engine is cold, repaired by replacing the manifolds. The bulletin's diagnosis starts by listening for a tick that stops once the engine has warmed up. The leak is still there, though, and the tick can come back on the next cold start.

Not every manifold leak waits for a cold engine. A Nissan bulletin for some older Frontier pickups, summarized by Vehicle Service Pros, describes a tick under acceleration that can sound like spark knock (a metallic pinging from the engine), fixed with a new manifold because the original may be cracked or warped.

Other things under the hood tick too, including valve parts inside the engine, and a squeal at start-up is a different noise that points elsewhere, such as a squealing serpentine belt.

A louder rumble, popping or hissing

Walker Exhaust Systems, an exhaust parts maker, lists a loud rumble, especially while accelerating, and popping or hissing that comes and goes as signs of a leak. It adds two less obvious ones: less pickup when you press the gas, and more trips to the gas station, because a leak can upset the engine's air-fuel balance.

Walker names rust, rough roads, and failed hangers or worn rubber isolators as common causes. Rust gives a leak a place to start, while rough roads and loose mounts let the system shake and knock until parts wear through or weaken.

Rattles and buzzes from underneath: heat shield or leak?

The exhaust hangs under the car on hangers with rubber isolators, and thin metal heat shields sit around the hottest parts to keep heat away from the floor and nearby components. When a shield's straps or fasteners loosen, it can rattle or buzz against the pipe or muffler. GM, for example, has told technicians that loose muffler heat shield straps can let the shield buzz while the vehicle is running.

A rattle can also be a broken hanger or clamp, part of the system touching the underbody, or loose baffles inside the muffler, which BC's vehicle standards list as a defect. A leak at a nearby joint can sound much the same, which is why a rattle is worth a proper look with the car up on a hoist.

Don't crawl under a running car, or one that's just been driven, to find the noise. Exhaust parts get hot enough to burn you, and with the engine running you'd be lying right next to the fumes.

Exhaust leaks and the check engine light

Modern engines use oxygen sensors in the exhaust to fine-tune the fuel mixture. Brake & Front End explains what a leak ahead of a sensor does: exhaust puffs out through the gap, and between pulses, outside air is drawn back in. The extra oxygen makes the sensor read lean, so the engine computer adds fuel to compensate. If the leak is big enough, that correction reaches its limit and the computer sets a lean code, such as P0171, which turns on the check engine light.

So the light can be the first sign of a leak you haven't heard yet. A lean code has other possible causes too, which is why it takes computerized diagnostics, not just reading the code, to find the real one. For what a steady light means, and what to do if it's flashing, see check engine light: solid vs flashing.

What BC rules say about exhaust leaks and loud exhausts

BC's Motor Vehicle Act Regulations cover both.

• A working muffler (s. 7.03). A vehicle with a gas or diesel (internal combustion) engine must have a muffler that cools the exhaust gases and expels them without excessive noise. You can't drive with the muffler cut out or disconnected, with baffles or other parts removed, with the outlet opened up or widened, or with anything added that makes the exhaust louder or lets it shoot flame.
• No leaks (Schedule, Standard 22). Under the regulations' standards of safety and repair, an exhaust system must not have loose or leaking joints, seams or holes. The muffler must not have loose interior baffles or patches, the system must be securely fastened, no part of it may pass through the passenger compartment, and it must not give off excessive fumes or smoke.
• No loud and unnecessary noise (s. 7A.01). Starting, driving or revving a vehicle in a way that causes loud and unnecessary noise from the engine or exhaust is prohibited.

ICBC also lists a faulty exhaust among the typical reasons a road test may be cancelled. It calls a leaking exhaust pipe or missing muffler unsafe and dangerous, and excessively loud mufflers illegal. That matters if a new driver in your household is about to take a road test in the family car.

What an exhaust inspection looks at

Walker's exhaust inspection and noise troubleshooting guidance for technicians, together with the manifold and heat-shield points above, give a fair picture of the usual steps.

What gets repaired depends on what's found: a loose heat shield, a hanger, a section of pipe, a gasket or a manifold. West Yale's exhaust system service comes with upfront pricing and no unnecessary upsells.

Common questions

Why does my car smell like exhaust inside?

Exhaust is getting into the cabin from somewhere. A leak is one cause, but the CDC also warns about a tailpipe blocked by snow and driving with only the tailgate or hatch open, which pulls exhaust inside. The smell comes from the other exhaust gases, not the carbon monoxide, so it's a sign CO may be getting in too. Open the windows, stop when it's safe and don't keep using the car until the exhaust has been inspected. If anyone feels unwell, switch off the engine, get everyone into fresh air right away and call 9-1-1.

Is it safe to drive with an exhaust leak?

You can't tell by listening. A leak can let carbon monoxide into the cabin, you can't smell it, and ICBC calls a leaking exhaust pipe unsafe and dangerous. If there's any exhaust smell inside, don't keep driving it. If it's a new noise, there's no exhaust smell and no one feels unwell, book an inspection soon. Until then, treat it as a possible CO risk: drive it as little as you can, don't sit in it parked with the engine running, and never idle it in a garage. If anyone feels unwell at any point, stop somewhere safe, switch off the engine, get everyone into fresh air and call 9-1-1.

How often should the exhaust be checked?

The U.S. CDC recommends having a mechanic check the exhaust system of a car or truck every year, and in BC, ICBC includes it in its winter preparation list. Fall, before the windows go up for the season, is a sensible time, and a regular maintenance visit is an easy place to ask for it. Have it checked sooner if you've hit something hard underneath, or if any of the signs on this page show up.