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5.5 OBD-II Readiness Monitors & Mode $06 Data

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ASE A8 Engine Performance Certification Study Guide Exam

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1 Chapter 1: General Engine Diagnosis

1.1 Mechanical Engine Condition & Compression Diagnostics 1.2 Intake & Exhaust Vacuum Analysis 1.3 Engine Noise, Vibration, & Mechanical Component Diagnosis 1.4 Engine Fluid, Thermal, & Lubrication System Interactions 1.5 Starting, Stalling, & General Driveability Troubleshooting 1.6 Complaint Verification, Service Information Research & TSB/Recall Lookup 1.7 Valve Adjustment, Camshaft Timing & Variable Valve Timing (VVT/VVL) 1.8 Battery Condition, Parasitic Drain & Starting System Current Draw Testing 1.9 Charging System Diagnosis, Voltage Drop Testing & Accessory Drive Belts

2 Chapter 2: Ignition System Diagnosis & Repair

2.1 Primary & Secondary Ignition Circuit Fundamentals 2.2 Ignition System Architectures (Distributor, Waste-Spark, COP) 2.3 Ignition Timing, Position Sensors, & Control Modules 2.4 Ignition Scope Analysis & Waveform Interpretation 2.5 Ignition DTC Interpretation, Misfire Root-Cause Analysis & Module Service

3 Chapter 3: Fuel, Air Induction, & Exhaust Systems Diagnosis & Repair

3.1 Fuel Delivery Systems & Pressure Testing 3.2 Fuel Injection Technology & Injector Testing (PFI & GDI) 3.3 Air Induction, Throttle Controls, & Airflow Sensing 3.4 Forced Induction Systems (Turbochargers & Superchargers) 3.5 Exhaust System Service, Restriction & Leak Diagnosis 3.6 Fuel Tank, Filler Neck, Fuel Cap, Lines & Fuel Filtration Service 3.7 Air Filtration, Unmetered Air Leaks & Throttle Body Service and Relearn

4 Chapter 4: Emissions Control Systems Diagnosis & Repair

4.1 Positive Crankcase Ventilation (PCV) Systems 4.2 Exhaust Gas Recirculation (EGR) Systems 4.3 Evaporative Emissions Control (EVAP) Systems 4.4 Secondary Air Injection (AIR) & Catalytic Converter Protection

5 Chapter 5: Computerized Engine Controls Diagnosis & Repair

5.1 Engine Control Module Architecture & Sensor Inputs 5.2 Oxygen & Air-Fuel Ratio (AFR) Sensors 5.3 Short-Term & Long-Term Fuel Trim Analysis 5.4 OBD-II Diagnostic Strategies, DTCs, & Freeze Frame 5.5 OBD-II Readiness Monitors & Mode $06 Data 5.6 Inspection/Maintenance (I/M) Testing & Failure Diagnostics 5.7 Electrical Schematics, Symbols & DMM Circuit Measurement 5.8 Serial Data Bus Networks & Communication Fault Diagnosis 5.9 PCM/ECM Testing, Replacement, Programming & Relearn Procedures 5.10 No-Code Driveability Diagnosis & Interrelated System Faults

6 Chapter 6: Exam Strategy & Logistics

6.1 ASE A8 Exam Blueprint, Registration Logistics & Test-Day Strategy

5.5 OBD-II Readiness Monitors & Mode $06 Data

Key Takeaways Explain This Topic AI

OBD-II readiness monitors evaluate emission control systems, categorized into Continuous Monitors (Misfire, Fuel System, Comprehensive Components) and Non-Continuous Monitors (Catalyst, HO2S, EVAP, EGR, Secondary Air).

Non-continuous monitors execute self-tests only when strict universal or manufacturer-specific Drive Cycle enable criteria (fuel level 15%–85%, cold start ECT vs. IAT within 11°F, steady cruise speeds) are satisfied.

Mode $06 diagnostic data provides raw, unmasked diagnostic test results, Monitor IDs (MID), and Test IDs (TID) alongside minimum/maximum pass/fail threshold limits.

Mode $06 enables technicians to identify failing components or marginal system degradation (e.g., borderline misfiring cylinder or degrading catalyst) BEFORE a diagnostic trouble code (DTC) sets or illuminates the MIL.

Clearing DTCs or disconnecting the battery resets all non-continuous readiness monitors to 'Not Ready' or 'Incomplete', requiring specific drive cycle completion for state emissions inspection compliance.

Last updated: August 2026

5.5 OBD-II Readiness Monitors & Mode $06 Data

OBD-II systems are not passive code recorders; they are active automated testing platforms. The ECM continuously runs internal self-diagnostic routines designated as Readiness Monitors to verify that all emission-related components and subsystems are fully functional. When advanced driveability issues occur without setting a hard Diagnostic Trouble Code, technicians utilize Mode $06 (On-Board Diagnostic Test Results for Specific Monitored Systems) to inspect raw component test values and pinpoint marginal failures before the MIL illuminates.

  • Continuous vs. Non-Continuous Readiness Monitors
  • OBD-II monitors are divided into two operational categories: +---------------------------------------+
  • | OBD-II READINESS MONITORS |
  • +---------------------------------------+
  • |
  • +---------------------------+---------------------------+
  • | |
  • v v
  • +--------------------------+ +--------------------------+
  • | CONTINUOUS MONITORS | | NON-CONTINUOUS MONITORS |
  • | (Run constantly whenever | | (Require strict enable |
  • | engine is operating) | | criteria & drive cycle) |
  • +--------------------------+ +--------------------------+
  • | 1. Misfire Monitor | | 1. Catalyst Monitor |
  • | 2. Fuel System Monitor | | 2. Heated O2/AFR Monitor |
  • | 3. Comprehensive Comp. | | 3. EVAP System Monitor |
  • +--------------------------+ | 4. EGR / VVT Monitor |
  • | 5. Secondary Air Monitor |
  • +--------------------------+
  • 1. Continuous Monitors

These monitors run continuously during all engine operating conditions once the engine is running:

Misfire Monitor : Uses the CKP sensor to track microsecond crankshaft acceleration pulses, detecting single or multi-cylinder misfires.

Fuel System Monitor : Continuously monitors fuel trim values in Closed-Loop to detect extreme rich or lean calibration failure.

Comprehensive Component Monitor (CCM) : Continuously checks all major electronic inputs and outputs (sensors, solenoids, relays) for opens, shorts-to-ground, shorts-to-voltage, and out-of-range signal rationality.

2. Non-Continuous Monitors

These monitors run only once per qualifying drive cycle when specific engine operating parameters ( Enabling Criteria ) are satisfied:

  • Catalyst Monitor (TWC)
  • Heated Oxygen / AFR Sensor Monitor
  • Evaporative Emissions (EVAP) Monitor
  • Exhaust Gas Recirculation (EGR) / Variable Valve Timing (VVT) Monitor
  • Secondary Air Injection Monitor
  • Enabling Criteria & Drive Cycle Execution

For a non-continuous monitor to run and flip its status flag from 'Not Ready' / 'Incomplete' to 'Ready' / 'Complete' , the vehicle must be driven through a specific sequence known as an OBD-II Drive Cycle .

Universal Drive Cycle Enable Criteria Rules

If enabling criteria are violated, the ECM suspends the self-test until the next trip:

Cold Start Differential Requirement : Engine Coolant Temperature (ECT) and Intake Air Temperature (IAT) must be within 11°F (6°C) of each other at startup (verifying an overnight cold soak).

Fuel Level Window : Fuel tank level must be between 15% and 85% . (EVAP monitors abort if fuel level is <15% to prevent sloshing errors, or >85% due to lack of vapor expansion space).

Ambient Temperature Range : Ambient air temperature must be between 40°F and 95°F (4°C - 35°C).

Steady Cruise Phase : Sustained steady-throttle driving at 50-60 MPH for 5 to 10 minutes to run Catalyst and O2 sensor monitors.

Deceleration Phase : Coasting down from 55 MPH to 20 MPH without depressing the brake or clutch pedal to test EGR and EVAP vacuum draw.

Deep-Dive into Mode $06 Diagnostic Data

Standard scan tool OBD-II communications are divided into 10 diagnostic modes (SAE J1979 / ISO 15031-5):

  • Mode Diagnostic Function
  • Mode $01 Request Current Powertrain Diagnostic Data (Live PIDs)
  • Mode $02 Request Freeze Frame Data
  • Mode $03 Request Stored Emission-Related Diagnostic Trouble Codes
  • Mode $04 Clear / Reset Emission-Related Diagnostic Data & Monitors
  • Mode $05 Request Oxygen Sensor Monitoring Test Results (Legacy non-CAN)
  • Mode $06 Request On-Board Monitoring Test Results for Specific Monitored Systems
  • Mode $07 Request Pending Diagnostic Trouble Codes (Detected during current trip)
  • Mode $08 Request Control of On-Board System, Test or Component (Bi-directional)
  • Mode $09 Request Vehicle Information (VIN, Calibration IDs, CVN)
  • Mode $0A Request Permanent Diagnostic Trouble Codes (Cleared only by ECM after self-test pass)
  • Mode $06 Data Architecture

Mode $06 exposes internal ECM testing registers for non-continuous monitors. Each test displays:

Monitor ID (MID) : Identifies the system being tested (e.g., MID $21 = Catalyst Monitor Bank 1; MID $3C = EVAP 0.020 in. leak monitor; MID $A1 = misfire data aggregated across all cylinders).

Test ID (TID) : Identifies the specific test run inside that monitor (e.g., under the misfire MIDs, TID $0B = misfire average over the last completed drive cycles and TID $0C = misfire counts for the current drive cycle). Catalyst, EGR, and EVAP TIDs are largely manufacturer-defined, so look them up in service information rather than assuming a standard meaning.

Component ID (CID) : Identifies the individual component location.

Measured Test Value : The actual numeric performance value recorded during the drive cycle test.

Minimum / Maximum Limits : The calibrated pass/fail thresholds defined by the factory engineers. Sample Mode $06 Scan Tool Display (CAN Format):

  • -------------------------------------------------------------
  • Monitor: MID $21 (Catalyst Monitor Bank 1)
  • Test: Oxygen Storage Capacity (manufacturer-defined TID)
  • Value: 0.042 (Measured Ratio)
  • Min: 0.000
  • Max: 0.085 (Fail Threshold)
  • Status: PASS (Margin: 50% under max limit)
  • -------------------------------------------------------------
  • Monitor: MID $A4 (Misfire Cylinder 3 Data)
  • Test: TID $0C (Misfire counts, current drive cycle)
  • Value: 42 (Measured Misfires)
  • Min: 0
  • Max: 50 (Fail Threshold - DTC P0303 sets at 51)
  • Status: PASS (WARNING: Borderline failure! Misfires occurring without setting DTC)
  • -------------------------------------------------------------
  • Advanced Mode $06 Diagnostic Applications

Pinpointing Intermittent Misfires : When an engine exhibits a light surge under load but HAS NOT set a P0300 code, check the Mode $06 misfire MIDs (MID $A1 aggregates every cylinder; MIDs $A2 through $AB report cylinders 1 through 10 individually). A cylinder logging 42 misfires against a fail limit of 50 pinpoints an isolated ignition coil or plug failure long before a DTC triggers.

Evaluating EVAP Small Leaks (P0442 / P0455) : Mode $06 shows raw vacuum decay rates in Pascals or inches of water column. Comparing measured decay against maximum threshold confirms whether a minor seal leak has been resolved after installing a new gas cap.