For car owners and technicians alike, understanding the health of a vehicle’s engine is paramount. Modern vehicles are equipped with sophisticated On-Board Diagnostic (OBD) systems that constantly monitor engine performance and emissions control components. A crucial aspect of these systems is the use of Monitors In Car Engine Scans. These monitors are essentially self-tests that your car performs to ensure everything is functioning as it should.
This guide delves into the world of car engine monitors, explaining their significance in engine scans, particularly within the context of smog checks and vehicle diagnostics. We’ll break down the pass/fail standards for these monitors and explore common issues that can arise, ensuring you’re well-informed about this vital aspect of vehicle maintenance and compliance.
What are OBD Monitors and Why Do They Matter?
At the heart of your vehicle’s emission control system lies the OBD system, mandated in most modern cars. This system employs a series of readiness monitors. These are diagnostic tests that the car’s computer (Engine Control Module or ECM/PCM) runs to verify that emission control systems are working correctly. Think of them as regular health checks for different parts of your car’s emission system.
The OBD-II port, usually located under the dashboard, is the gateway to access your car’s diagnostic information, including monitor status.
These monitors are essential for several reasons:
- Emissions Compliance: They ensure your vehicle meets stringent emission standards, reducing harmful pollutants released into the environment.
- Early Problem Detection: Monitors can detect issues early on, often before you notice any drivability problems, preventing costly repairs down the line.
- Smog Check Requirements: In many regions, smog checks rely heavily on OBD monitor status to determine if your vehicle passes the emissions test.
Types of OBD Monitors in Car Engine Scans
OBD monitors can be broadly categorized into two main types:
-
Readiness Monitors (or OBDII Readiness Monitors): These monitors assess the status of various emission control systems. They run periodically or continuously, depending on driving conditions and vehicle design. Common readiness monitors include:
- Misfire Monitor: Detects engine misfires that can increase emissions and damage the catalytic converter.
- Fuel System Monitor: Checks the fuel delivery system for proper operation and fuel mixture control.
- Comprehensive Components Monitor (CCM): Monitors a wide range of engine and emission-related components for electrical and rationality faults.
- Catalyst Monitor: Evaluates the efficiency of the catalytic converter in reducing pollutants.
- Evaporative System (EVAP) Monitor: Checks for fuel vapor leaks in the evaporative emissions control system.
- Oxygen Sensor Monitor: Tests the functionality of oxygen sensors, which are crucial for fuel trim and catalyst efficiency.
- Oxygen Sensor Heater Monitor: Verifies the operation of oxygen sensor heaters, ensuring sensors reach operating temperature quickly.
- EGR/VVT Monitor: (Exhaust Gas Recirculation/Variable Valve Timing) Checks the EGR system for reducing NOx emissions and the VVT system for optimal engine performance and efficiency.
- Secondary Air System Monitor: (If equipped) Monitors the secondary air injection system, which helps reduce cold-start emissions.
- Heated Catalyst Monitor: (If equipped) Evaluates the performance of heated catalytic converters, which warm up faster for quicker emission control.
- Particulate Filter Monitor (Diesel): (Diesel vehicles) Monitors the diesel particulate filter (DPF) for soot accumulation and regeneration efficiency.
- NMHC Catalyst Monitor (Diesel): (Diesel vehicles) Monitors the Non-Methane Hydrocarbon (NMHC) catalyst, reducing hydrocarbon emissions.
- NOx Aftertreatment Monitor (Diesel): (Diesel vehicles) Checks the Selective Catalytic Reduction (SCR) system for reducing NOx emissions.
- Exhaust Gas Sensor Monitor (Diesel): (Diesel vehicles) Monitors sensors related to exhaust gas parameters in advanced diesel emission systems.
-
Continuous Monitors: These monitors run constantly whenever the engine is running and immediately detect malfunctions. The primary continuous monitors are:
- Misfire Monitor
- Fuel System Monitor
- Comprehensive Components Monitor (CCM)
The Check Engine Light, or Malfunction Indicator Lamp (MIL), illuminates when the OBD system detects a problem.
OBD Monitor Status and Smog Check Inspections
During a smog check, the status of OBD monitors is a critical factor in determining whether your vehicle passes or fails the OBD test portion. Smog check stations use specialized equipment to scan your vehicle’s computer and retrieve monitor status information.
Pass/Fail Standards for Readiness Monitors:
The number of incomplete readiness monitors allowed varies depending on the model year and fuel type of your vehicle. “Incomplete” means the monitor has not yet run and completed its self-test since the last time the vehicle’s computer memory was cleared (e.g., battery disconnection or DTC clearing).
| Model Year | Fuel Type | Number of Incomplete Monitors Allowed to Pass OBD Test |
|---|---|---|
| 1996-1999 | Gas (including gasoline, propane, natural gas) | Any one |
| 2000 and newer | Gas | Evaporative system only |
| 1998-2006 | Diesel | Zero |
| 2007 and newer | Diesel | Particulate Filter and Non-Methane HydroCarbon (NMHC) |
Important Notes:
- The misfire, fuel, and comprehensive component continuous monitors are always ignored during an OBD test on gasoline vehicles. They are continuously running, so their readiness status isn’t relevant for the smog check.
- For 2007 and newer diesel vehicles, only the Particulate Filter and NMHC monitors can be incomplete to pass. All other monitors must be complete.
Malfunction Indicator Lamp (MIL) Standards:
The MIL, often called the “Check Engine Light,” is another critical component of the OBD test. The standards are straightforward:
| Condition | Pass/Fail | Standard |
|---|---|---|
| MIL illuminates when key on, engine off (KOEO) | Pass | Indicates the MIL is functional. |
| MIL turns off when engine running (KOER) | Pass | Indicates no active emissions-related faults. |
| MIL does not illuminate when key on, engine off (KOEO) | Fail | Indicates a problem with the MIL circuit or bulb. |
| MIL illuminates when engine running (KOER) | Fail | Indicates an active emissions-related fault and stored Diagnostic Trouble Codes (DTCs). |
If the MIL is commanded on when the engine is running, the vehicle will fail the smog check’s OBD test.
Communication Standards:
For the smog check equipment to assess the monitors, it needs to communicate with your vehicle’s computer. Communication failures can lead to a failed OBD test. Common causes include:
- Damaged OBD connector
- Wiring issues
- Aftermarket stereo installations interfering with communication
- Computer issues in the vehicle
Permanent Diagnostic Trouble Code (PDTC) Standards:
Vehicles from model year 2010 and newer are also checked for Permanent Diagnostic Trouble Codes (PDTCs). PDTCs are similar to regular DTCs but cannot be cleared by simply using a scan tool or disconnecting the battery. They only clear themselves after the OBD system verifies the fault is no longer present after multiple drive cycles.
- For 2010 and newer vehicles, the presence of any PDTC will result in a failed smog check, regardless of whether the MIL is on or off.
- However, PDTCs are ignored if the vehicle has completed at least 15 warm-up cycles and been driven 200 miles since the last DTC clearing. This allows time for the system to self-clear PDTCs if the issue is resolved.
Common Issues Affecting OBD Monitors in Car Engine Scans
Several factors can prevent OBD monitors from completing or cause issues during engine scans:
- Drive Cycle Requirements: Some monitors require specific driving conditions (speed, temperature, engine load, duration, etc.) to run. These “drive cycles” can be challenging to perform in normal traffic. Vehicle owner’s manuals or repair information may contain drive cycle procedures.
- Underlying Faults: If there’s an actual problem in an emission control system, the corresponding monitor may not complete until the fault is diagnosed and repaired.
- Recent Repairs or Battery Disconnection: Any repair work that involves disconnecting the battery or clearing DTCs will reset the monitor status to “incomplete.” Monitors need to be rerun after repairs.
- Vehicle-Specific Issues: Certain vehicle makes and models are known to have design anomalies or software issues that can cause monitors to be difficult to complete, communication problems, or false readings.
Vehicles of Interest: Common OBD Monitor Issues
The original document provides extensive tables listing specific vehicle makes and models known to have OBD test issues. These tables are invaluable for technicians and inspectors. Here are a few examples of common problems and solutions highlighted in the original document:
OIS Vehicles of Interest (OBD Inspection System): These are vehicles with known issues during standard OBD inspections.
| Make | Year | Model & Engine | Issue | Cause & Remedy | Inspector Instruction |
|---|---|---|---|---|---|
| Audi | 2000-2004 | A4 & A6 | No OBD Communication | Broken ground wire in ABS module | Repair ground wire per Audi TSB |
| BMW | 2000 | M52 (TU) Engine | Oxygen Sensor Monitor Not Set | DME Software Error | Reprogram DME with updated software |
| Chevrolet | 2019 | Express 2.8L Diesel | Exhaust Gas Sensor Monitor Incomplete | ECM Software Issue | ECM Reprogramming Recall Needed |
| Ford | 2020-2022 | Escape (Gas & Hybrid) | No Communication with BAR-OIS | Gateway Module Software Issue | Software Update at Ford Dealer Needed |
PDTC Vehicles of Interest (Permanent Diagnostic Trouble Codes): These vehicles are known to have issues with PDTCs not clearing correctly.
| Make | Year | Model & Engine | Issue | Cause & Remedy | Inspector Instruction |
|---|---|---|---|---|---|
| Audi | 2010-2012 | Q7 3.0 TDI Diesel | PDTCs (P0087, etc.) Won’t Clear | No Remedy Available | BAR-OIS Ignores These Codes |
| Chrysler, Dodge, Jeep, Ram | 2010-2015 | Various Models | PDTCs Won’t Clear | Software Issue | Reflash PCM per Recall V51 |
| Ford | 2011-2014 | Mustang 3.7L & 5.0L | PDTC P0315 Won’t Clear | Vehicle Not Self-Clearing | Refer to Ford Customer Satisfaction Program |
BAR-97 EIS Vehicles of Interest (Older Vehicles, BAR-97 Equipment): These are older (1996-1999) vehicles with monitor issues when tested with older BAR-97 smog check equipment. For many of these, the EIS (Emission Inspection System) is programmed to ignore readiness status due to known vehicle limitations.
| Make | Year | Model & Engine | Issue | Cause & Remedy | Inspector Instruction |
|---|---|---|---|---|---|
| BMW | 1996 | 7-Series, 8-Series | Monitors Difficult to Complete | EIS Ignores Readiness Status | Test Normally |
| Chrysler, Dodge, Eagle, Plymouth | 1996 | Various Models | Monitors Reset at Key-Off | Recall Campaign Available | Comply with Recall, Then Test |
| Toyota | 1996-1999 | All Models | Monitors Difficult to Complete | Follow Toyota Drive Cycles | Test Normally |
Tips for Dealing with OBD Monitors During Engine Scans
- Understand Your Vehicle’s Requirements: Consult your owner’s manual or repair information to understand the specific drive cycle requirements for your vehicle’s monitors.
- Perform a Drive Cycle: If monitors are incomplete, attempt to perform the appropriate drive cycle. Ensure you do this safely and legally.
- Check for Technical Service Bulletins (TSBs) and Recalls: For vehicle-specific monitor issues, check for TSBs or recalls from the manufacturer that may provide software updates or repair procedures.
- Allow Time After Repairs: After any emission-related repairs or battery disconnection, allow sufficient driving time and conditions for monitors to complete before a smog check.
- Professional Diagnosis: If monitors persistently remain incomplete or you suspect a malfunction, seek professional diagnosis from a qualified mechanic.
Conclusion: Monitors as Key Indicators of Vehicle Health
Monitors in car engine scans are a crucial window into your vehicle’s emission system health. Understanding their function, pass/fail criteria, and potential issues is essential for vehicle owners and technicians. By paying attention to monitor status, you can ensure your vehicle is running cleanly, efficiently, and compliant with emission regulations. This knowledge empowers you to proactively maintain your vehicle and address potential problems before they escalate, contributing to cleaner air and a healthier environment.
For certified smog check technicians, detailed resources like the original document are indispensable for navigating vehicle-specific OBD testing complexities and ensuring accurate and efficient inspections. Understanding these nuances allows for better service to customers and upholds the integrity of emissions testing programs.
