7.1 Inspection and Maintenance Programs

Every modern Advanced Engine Performance technician spends a significant share of bench time on I/M failures. The L1 exam tests your understanding of why an Inspection and Maintenance program flagged a vehicle, what counts as a pass, and how to legally and verifiably repair the cause.

Federal Mandate, State Implementation

The Clean Air Act (CAA) is the federal law that authorizes the Environmental Protection Agency (EPA) to require I/M programs in metropolitan areas that fail to meet National Ambient Air Quality Standards (NAAQS). The EPA does not run the inspection stations directly — it sets minimum performance criteria and audits state-administered programs.

States differ on:

• Test geography — only non-attainment counties, statewide, or by registration class
• Test type — OBD-II network test, ASM (Acceleration Simulation Mode) on a dyno, IM240 transient dyno test, two-speed idle, or evaporative pressure/purge
• Cut points — pollutant thresholds in grams-per-mile or percent CO
• Exemptions — new-vehicle grace period (often four years), antique vehicles, electric/hybrid logic, or low-mileage waivers
• Waiver dollar amounts — repair cost spent before a hardship waiver is granted

OBD-II I/M Network Test

For model-year 1996 and newer light-duty gasoline vehicles, almost every state replaced the tailpipe sniffer with an OBD-II network test. A scan tool connects to the Data Link Connector (DLC) and queries the powertrain control module for three pass/fail conditions.

The MIL bulb check is sometimes overlooked. A burned-out or disconnected MIL bulb fails the test independently because the lamp must be able to alert the driver if a fault later occurs.

The Eight Standardized Readiness Monitors

OBD-II requires the ECM to run self-tests of emission control subsystems. Each test is called a readiness monitor and reports either Complete/Ready, Incomplete/Not Ready, or Not Supported. Monitors fall into two groups.

Continuous Monitors (always running)

• Misfire Monitor — tracks crank speed irregularities cylinder-by-cylinder
• Fuel System Monitor — watches short-term and long-term fuel trims for excursions
• Comprehensive Component Monitor (CCM) — checks every input/output for opens, shorts, rationality

Continuous monitors are always shown as Complete on a properly running vehicle because they evaluate constantly during normal driving.

Non-Continuous Monitors (require specific enable criteria)

• Catalyst Monitor — compares pre- and post-cat oxygen sensor switching activity
• Heated Catalyst Monitor — verifies electric catalyst heater operation (where used)
• Evaporative (EVAP) System Monitor — pressure or vacuum decay test of fuel/vapor lines
• Secondary Air Injection (AIR) Monitor — confirms AIR pump delivery during cold start
• A/C Refrigerant Monitor — leak check of the air-conditioning circuit (rarely used today)
• Oxygen Sensor Monitor — tests upstream O2 response time and amplitude
• Oxygen Sensor Heater Monitor — verifies heater current and warm-up rate
• EGR Monitor — verifies Exhaust Gas Recirculation flow under enabling conditions

Non-continuous monitors only run when very specific enable criteria are met (coolant temperature, intake air temperature, fuel level, vehicle speed, time at idle, deceleration without braking). Clearing codes resets all monitors to Not Ready.

Monitor Not-Ready Allowances

Most states follow the EPA recommendation:

• Gasoline 1996–2000 — up to two non-continuous monitors not-ready
• Gasoline 2001 and newer — up to one non-continuous monitor not-ready
• Diesel — generally one non-continuous monitor not-ready
• Some strict states — zero not-ready allowed

A vehicle whose battery was just disconnected, ECM reflashed, or codes cleared will typically have multiple monitors Not Ready and must be driven through the appropriate drive cycle before retest.

Permanent DTCs (Mode $0A)

Permanent DTCs were added in 2010 model year requirements (and earlier for some manufacturers) to defeat the practice of clearing codes immediately before an I/M test. A code becomes Permanent after the ECM confirms it has been present and has set the MIL.

A Permanent DTC will fail an I/M test even if the MIL has been turned off and no confirmed code is currently set. The only path to clear it is to repair the root cause, drive the vehicle through the relevant monitor's enable criteria, and let the monitor pass.

Why the L1 Cares About Permanent Codes

A classic L1 scenario: a customer brings a vehicle that just failed I/M for a P0420. A previous shop cleared the code and told the customer to "drive it for a while." The MIL is now off, but the inspection station still failed the vehicle. The reason is the Permanent DTC — it remained even though the confirmed code was wiped. The correct response is to diagnose and repair the catalyst efficiency cause, then run the catalyst monitor enable criteria so the ECM clears Mode $0A automatically.