Plug in any check-engine code and get a plain-English explanation, common causes, and a realistic Canadian repair cost range — then find a trusted shop near you.
The downstream oxygen sensor on bank 1 is reading too similarly to the upstream sensor, which means the catalytic converter is no longer scrubbing exhaust gases efficiently. The car will still drive, but it will fail an emissions test (in provinces that still test) and the catalyst will keep degrading until it's replaced.
See causes & costThe engine on bank 1 is running with too much air relative to fuel. Long-term fuel trims have shifted to add more fuel to compensate. Common with older vehicles — usually a vacuum leak or a tired MAF sensor.
See causes & costThe engine is misfiring on more than one cylinder, or on cylinders the computer can't isolate. A misfire means the cylinder isn't burning fuel properly — you may feel a rough idle, hesitation, or shaking, especially under load.
See causes & costThe engine computer detected a misfire on cylinder 1 — that cylinder isn't completing a normal combustion event reliably. You'll usually feel a rough idle or hesitation, and the check engine light may flash on heavy throttle. Continued driving with an active misfire can wash down the catalytic converter and turn a $300 plug-and-coil job into a $1,500+ catalyst replacement.
See causes & costThe engine isn't reaching its target operating temperature in the time the computer expects. In Canadian winters this is a very common code — the cabin heater feels weak and fuel economy drops because the engine stays in warm-up mode longer than it should.
See causes & costAn evaporative-emissions code. EVAP codes don't affect drivability — they mean the system that captures gasoline vapors from your fuel tank isn't sealing or flowing the way the computer expects. In Canada, where fuel cap and vent-solenoid issues are very common in winter, start with the fuel cap before paying for diagnostic time.
See causes & costAn evaporative-emissions code. EVAP codes don't affect drivability — they mean the system that captures gasoline vapors from your fuel tank isn't sealing or flowing the way the computer expects. In Canada, where fuel cap and vent-solenoid issues are very common in winter, start with the fuel cap before paying for diagnostic time.
See causes & costThe downstream oxygen sensor on bank 2 is reading too similarly to the upstream sensor, which means the catalytic converter is no longer scrubbing exhaust gases efficiently. The car will still drive, but it will fail an emissions test (in provinces that still test) and the catalyst will keep degrading until it's replaced.
See causes & costSame as P0171 but on bank 2. The engine bank with cylinder #2 (typically the side away from cylinder #1) is running too lean. On V6/V8 engines, P0171 + P0174 together usually point to a shared problem like a dirty MAF or a vacuum leak after the throttle body.
See causes & costAn evaporative-emissions code. EVAP codes don't affect drivability — they mean the system that captures gasoline vapors from your fuel tank isn't sealing or flowing the way the computer expects. In Canada, where fuel cap and vent-solenoid issues are very common in winter, start with the fuel cap before paying for diagnostic time.
See causes & costA transmission-side fault. Modern automatics use solenoids, speed sensors, and a transmission control module (TCM). Many shifting-quality complaints (harsh shifts, slipping, no engagement) trace back to one of these subsystems. Most transmission codes warrant a shop visit promptly — continued driving with a slipping or overheating transmission can turn a $400–$800 solenoid into a full rebuild.
See causes & costWhatever module set this code can't reach the engine computer over the CAN bus. Often pops alongside many other codes when there's a wiring or connector issue, a discharged battery, or a failed module. Cold-weather connectors and rodent damage are common Canadian causes.
See causes & costEvery vehicle sold in Canada and the US since 1996 has an OBD-II self-diagnostic port — a 16-pin trapezoid usually under the steering column. When the vehicle's computer detects a problem, it stores a 5-character code (like P0420) and turns on the check-engine light. A scan tool reads the code; this site translates it into plain English.
The first character tells you the system: P = powertrain (engine, transmission), B = body (airbags, climate, lighting), C = chassis (ABS, traction control), U = network (CAN bus communication). The next four digits identify the specific fault. Codes ending in 0 as the second character are generic SAE codes that mean the same thing on every car; codes with 1 or higher are manufacturer-specific.
OBD-II (On-Board Diagnostics II) is the standard self-diagnostic system in every passenger vehicle sold in North America since 1996. When something goes wrong, the vehicle's computer stores a 5-character code (like P0420) and turns on the check-engine light. Plug a $30 scan tool or a phone OBD adapter into the port under the dash, read the code, and look it up here in plain English.
P codes are powertrain (engine and transmission). B codes are body (airbags, lighting, seats, climate). C codes are chassis (ABS, traction control, suspension). U codes are network/communication faults between the vehicle's modules. The fourth character — 0 for generic SAE codes, 1+ for manufacturer-specific — tells you whether it's a universal definition or specific to your make.
You can, but the code will come back if the underlying problem is still there — and you've now lost the freeze-frame data that helps a technician diagnose the issue. For active misfires, transmission codes, and overheating-related codes, continuing to drive can turn an inexpensive repair into an expensive one. Clearing codes also resets your emissions readiness monitors, which means you'll fail an inspection in provinces that still test until you drive enough miles for the monitors to re-set.
Costs are rough Canadian (CAD) ranges that blend reasonable parts prices with shop labor at $110–$165/hr (typical 2026 posted Canadian independent rates). They're meant for budgeting, not as a quote. Your actual cost depends on your vehicle, your province, and the specific diagnosis. When we don't have a confident range, we say "Varies — get a quote" rather than make up a number.
The code tells you what symptom the computer noticed, not always the root cause. P0420 (catalyst inefficiency) can be a $1,500 catalytic converter — or a $40 oxygen sensor, or a $250 ignition coil, depending on what's actually failing. A shop with a real bidirectional scan tool can verify the diagnosis before parts get thrown at the problem. Use this lookup to understand what's going on, then use the directory to find a shop you can trust.
Reading the code is step one. Our directory lists vetted family-owned shops across Canada that will give you a fair, defensible diagnosis before throwing parts at the problem.
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