Understanding the evaporative emission (EVAP) system in your 2012 Jeep is crucial for maintaining its performance and staying compliant with emission standards. The On-Board Diagnostics II (OBD2) system plays a vital role in monitoring this system and alerting you to potential issues. This article delves into the diagnostic tests your 2012 Jeep Obd2 system conducts on the EVAP system, helping you understand what’s happening under the hood.
The EVAP system in your 2012 Jeep is tested using two primary methods: a non-intrusive test performed when the engine is off, and an intrusive test conducted while the engine is running. These tests are designed to detect leaks of different sizes within the system, ensuring that harmful fuel vapors are not released into the atmosphere.
Non-Intrusive EVAP System Test on Your 2012 Jeep
The non-intrusive test is designed to detect small leaks in your 2012 Jeep‘s EVAP system. This test occurs when the engine is off and relies on the Evaporative System Integrity Monitor (ESIM) and its associated switch. During engine-off conditions, the ESIM weights seal the EVAP system. As the system cools down after operation or due to normal temperature changes, a vacuum can form within the sealed system.
If the EVAP system is properly sealed, this vacuum will increase. When the vacuum reaches approximately 1 inch of water (H20), a vacuum switch within the ESIM closes. This switch closure sends a signal to the Powertrain Control Module (PCM), the computer managing your 2012 Jeep‘s engine and emissions.
For the non-intrusive small leak test to pass on your 2012 Jeep OBD2 system, the ESIM switch must close within a calculated timeframe and within a specific number of key-off events. If the PCM doesn’t receive the signal from the ESIM switch within the expected parameters, the test is deemed inconclusive. In such cases, the system will then prepare to run the more thorough intrusive test during the next engine start cycle.
Intrusive EVAP System Test on Your 2012 Jeep
If the non-intrusive test is inconclusive, or if the system needs to check for larger leaks, the intrusive EVAP system test is initiated on your 2012 Jeep. This test is performed while the engine is running and is designed to detect medium to large leaks. Several conditions must be met for this intrusive test to begin, ensuring accurate and reliable results from your 2012 Jeep OBD2 system:
- Cold Start Condition: The engine coolant temperature must be within 50°F (10°C) of the ambient temperature. This indicates a cold start, a necessary condition for the test.
- Fuel Level: The fuel tank level must be between 12% and 88%. This range ensures proper system operation during the test.
- Closed Loop Operation: The engine must be in closed loop operation. This means the engine management system is using feedback from sensors, like oxygen sensors, to precisely control the air-fuel mixture.
- Manifold Vacuum: The manifold vacuum must be greater than a minimum specified value. This ensures sufficient vacuum is available for the test.
- Ambient Conditions: The ambient temperature must be between 39°F and 98°F (4°C and 37°C), and the vehicle elevation must be below 8500 feet (2591 meters). These environmental parameters are necessary for the test to run correctly.
Once these conditions are met, the intrusive test proceeds using a method called vacuum decay. The PCM activates the purge solenoid to create a vacuum within the EVAP system of your 2012 Jeep. Then, the PCM carefully monitors the time it takes for this vacuum to dissipate.
- Large Leak: If the vacuum switch opens very quickly, it indicates a large leak in the EVAP system.
- Small Leak: If the switch opens after a predetermined amount of time, it may indicate a smaller leak.
- General EVAP Failure: If the switch does not close at all during the test, it suggests a general failure within the evaporative system.
Following the medium/large leak test, and only if it passes the small leak test, the purge monitor test is executed. This test checks the integrity of the hose connecting the purge valve to the throttle body or intake manifold in your 2012 Jeep.
Purge Monitor Test Stages
The purge monitor test is a two-stage process designed to verify the proper function of the purge system in your 2012 Jeep.
- Stage One (Non-Intrusive): The PCM monitors the purge vapor ratio. If this ratio is above a calibrated specification, the first stage of the monitor passes.
- Stage Two (Intrusive): This stage is only initiated if stage one fails. During stage two, the PCM commands the purge solenoid to operate at a specific rate to force an update of the purge vapor ratio. This ratio is then compared to a calibrated specification. If it is less than specified, a one-trip failure is recorded.
ESIM Switch Stuck Closed Monitor
Another diagnostic check performed by your 2012 Jeep OBD2 system is the ESIM switch stuck closed monitor. This test is a power-down test that runs when the engine is turned off. When the PCM registers 0 RPM, indicating the engine is off, it energizes the purge solenoid for up to 30 seconds. This action vents any vacuum that might be trapped in the EVAP system.
If the ESIM switch opens during this test, or if it was already open before the test began, the monitor passes. However, if the switch remains closed, the monitor fails, resulting in a two-trip Malfunction Indicator Lamp (MIL) activation – meaning the check engine light will illuminate after the fault is detected on two separate drive cycles. For advanced diagnostics, a scan tool can be used to manually trigger the ESIM switch stuck closed monitor test.
Understanding these 2012 Jeep OBD2 evaporative system tests can be invaluable for diagnosing potential emission issues. If your check engine light illuminates, knowing how these tests function can help you or your mechanic pinpoint the problem more efficiently, keeping your 2012 Jeep running cleanly and efficiently.
