For the average driver, the check engine light (MIL) is a signal from the emissions/powertrain system that ranges from minor (e.g., loose gas cap or small EVAP leak) to urgent faults. Severity matters: a flashing MIL indicates an active misfire that can overheat and damage the catalytic converter—U.S. EPA advises minimizing driving and seeking immediate service in that case. Typical check‑engine repairs, when addressed promptly, average in the low‑$400s per incident, and the most common causes remain catalytic‑converter efficiency codes, oxygen sensor faults, EVAP leaks, and ignition issues, per CarMD’s Vehicle Health Index. By contrast, delayed misfire‑related damage can require catalytic converter replacement that commonly runs about $1,300–$2,500+.
Despite that, many people are tempted to ignore a steady (non‑flashing) light. Current U.S. indicators show why: AAA continues to report widespread deferral of maintenance due to time and cost pressures; repair prices and insurance premiums have risen, with the CPI showing continued increases for vehicle maintenance/repair and double‑digit gains for motor‑vehicle insurance (BLS CPI); and only about six in ten adults say they could cover a $400 emergency expense with cash or its equivalent (Federal Reserve SHED)—roughly the size of an average check‑engine repair (CarMD). An aging vehicle fleet also contributes: the average U.S. light vehicle reached a record 12.6 years in 2024 and 12.7 years in 2025 (S&P Global Mobility), increasing the likelihood of MIL‑related faults.
To understand how quickly people respond when a MIL comes on, we synthesized the most current U.S. data sources that shed light on behavior and outcomes: average repair costs and common causes (CarMD), maintenance deferral trends (AAA), fleet age (S&P Global Mobility), and inspection performance (California BAR). Where direct, recent U.S. time‑to‑action survey percentages are limited, we also note corroborating behavior from the UK’s RAC Report on Motoring 2024, clearly labeled as UK data.
Study findings
- Average U.S. check‑engine repairs typically land in the low‑$400 range when handled promptly, and top causes remain catalytic‑converter efficiency codes (P0420/P0430), oxygen sensors, EVAP leaks, and ignition issues (CarMD).
- A flashing MIL signals a misfire that can rapidly damage the catalyst—minimize driving and seek service immediately (EPA); catalytic converter replacement commonly costs $1,300–$2,500+, far more than typical upstream fixes.
- Inspection programs reveal delay in action: California’s Smog Check data show ongoing initial failures tied to MIL commanded on and OBD readiness issues, meaning many vehicles reach inspection with unresolved faults (California BAR).
- Ignoring emissions‑control faults wastes fuel: fixing a serious issue like a faulty oxygen sensor can improve fuel economy by as much as 40% (FuelEconomy.gov).
- Economic and demographic context matter: only about six in ten U.S. adults can cover a $400 surprise expense (Federal Reserve SHED), while the vehicle fleet’s record age (12.6 years in 2024; 12.7 years in 2025) elevates MIL incidence and deferral pressures.
- Gender and age differences: younger owners are more likely to defer non‑urgent work and rely on digital scheduling/updates, while older owners show higher provider loyalty; women are less likely than men to perform DIY repairs and more likely to prefer DIFM channels. These patterns are reported by J.D. Power (2025), Cox Automotive, and IMR Automotive Research. UK corroboration: the RAC 2024 Report on Motoring finds many drivers continue to drive with warning lights illuminated before acting (UK context).
It’s smart to get the code(s) read quickly to confirm severity. Free in‑person scans are widely available at major parts retailers—see AutoZone Fix Finder, O’Reilly, and Advance Auto Parts—which can show DTCs and readiness status. These scans are a starting point, not a full diagnosis; Consumer Reports recommends professional evaluation for complex issues. Shops typically charge dedicated diagnostic time (often around an hour; see RepairPal).
So then why do some people ignore getting this looked at?
Cost and time are leading reasons. Repair prices and insurance premiums have remained elevated (BLS CPI), and only about six in ten adults have $400 available for an unexpected expense (Federal Reserve SHED)—roughly the size of a typical check‑engine repair (CarMD). AAA reports that many owners postpone service until a warning indicator forces action, increasing the risk of costlier downstream repairs.
Another factor is uncertainty: some MILs resolve after the PCM completes drive cycles and all readiness monitors run, which can auto‑clear certain transient conditions. Still, relying on that is risky. Vehicles that reach inspection with a MIL on or incomplete monitors will fail until repaired and monitors set (California BAR). Newer vehicles also add connected‑car alerts and remote diagnostics: service‑oriented and IP‑based diagnostics (ASAM SOVD), OTA software update processes (UN R156), standardized signal catalogs (COVESA VSS), and cloud data pipelines (AWS IoT FleetWise) enable remote health checks and, in some cases, software‑based remediation after the system detects and verifies a fix.
Vehicle age and budgets reinforce the pattern: with the U.S. fleet at 12.6 years in 2024 and 12.7 years in 2025 (S&P Global Mobility), owners of older, out‑of‑warranty cars are more likely to triage non‑safety faults signaled by a steady MIL until an inspection or drivability symptom forces repair—an effect reflected in California BAR failure reasons tied to MIL and readiness.
You Should Take Your Car to a Mechanic as Soon as Possible
Don’t wait to confirm what the light means. If the MIL is flashing, follow EPA guidance: minimize driving and seek immediate service to avoid catalyst damage. Even with a steady light, prompt code retrieval and diagnosis help you avoid downstream failures and keep inspection readiness on track—vehicles with the MIL on or incomplete monitors will not pass Smog Check until repaired and validated (California BAR). Free retailer scans can provide the DTCs and readiness status (AutoZone; O’Reilly; Advance Auto Parts), but use a professional diagnostic for complex faults (Consumer Reports).
Small faults can snowball if ignored. Addressing upstream causes like oxygen sensors or ignition components early is typically far cheaper than replacing a damaged catalytic converter ($1,300–$2,500+). Fixing serious issues (e.g., a faulty oxygen sensor) can also improve fuel economy by up to 40% (FuelEconomy.gov), reducing ongoing fuel costs and emissions. Pair timely diagnosis with modern reminders: connected‑car apps and dealer systems increasingly push service alerts, recall notices, and easy scheduling (J.D. Power 2025), while national campaigns emphasize basics like tire care and regular checks (USTMA) and routine VIN recall lookups (NHTSA).
Study methodology
- This article synthesizes current datasets and advisories: CarMD Vehicle Health Index (average costs and common MIL causes), AAA (maintenance deferral behavior), S&P Global Mobility (fleet age), California BAR (inspection outcomes), EPA, FuelEconomy.gov, RepairPal, BLS CPI, Federal Reserve SHED, plus demographic and education trends from J.D. Power 2025, Cox Automotive, IMR, USTMA, NHTSA, and UK corroboration from the RAC 2024 Report on Motoring (clearly labeled as UK).
- Findings reflect the most recent publications available from these sources in 2024–2025 and emphasize U.S. data for costs, inspection readiness, economic context, and diagnostic technology (e.g., ASAM SOVD; UN R156; COVESA VSS; AWS IoT FleetWise).
- No new personal data were collected for this synthesis; all information comes from aggregated or published research and official reports cited above.
