Integrated Air Fuel Catalyst Monitor

Description and Operation 1-111

Catalyst Efficiency Monitor

Some vehicles that are part of the low emission vehicle (LEV) catalyst monitor phase in, monitor less than 100% of the catalyst volume. Often this is the first catalyst brick of the catalyst system. Partial volume monitoring is done on LEV and ultra low emission vehicle (ULEV) vehicles in order to meet the 1.75 emission standard. The rationale for this strategy is the catalyst nearest the engine deteriorates first, allowing the catalyst monitor to be more sensitive and illuminate the MIL correctly at lower emission standards.

Some applications use partial volume monitoring, where the rear HO2S is located after the first light off catalyst can or after the second catalyst can in a three can per bank system (a few applications placed the HO2S in the middle of the catalyst can, between the first and second bricks). For additional HO2S information, refer to the Heated Oxygen Sensor (HO2S) Monitor in this section.

Index ratios for ethanol (flex fuel) vehicles vary based on the changing concentration of alcohol in the fuel. The threshold to determine a concern typically increases as the percent of alcohol increases. For example, a threshold of 0.5 may be used at E10 (10% ethanol) and 0.9 may be used at E85 (85% ethanol). The thresholds are adjusted based on the percentage of alcohol in the fuel. Standard fuel may contain up to 10% ethanol.

The PCM calibration prevents the catalyst monitor from running on a new vehicle until 60 minutes of time has accumulated with the catalyst temperature greater than 426°C (800°F) or 483 km (300 miles) have accumulated. A replacement PCM or updated calibration does not prevent the catalyst monitor from running.

1. The HO2S can be located in various configurations to monitor different kinds of exhaust systems. Inline engines and many V engines are monitored by their individual bank. A rear HO2S is used along with the front, fuel control universal HO2S for each bank. Two sensors are used on an inline engine and 4 sensors are used on a V engine. Some V engines have exhaust banks that combine into a single underbody catalyst. These systems are referred to as Y pipe systems. They use only one rear HO2S along with the 2 front, fuel control universal HO2S. The Y pipe system uses 3 sensors in all. For Y piped systems, the 2 front universal HO2S signals are combined by the PCM software to infer what the exhaust oxygen content would have been in front of the monitored catalyst. The inferred front exhaust oxygen content and the rear HO2S signal is then used to calculate the index ratio.

2. The malfunction indicator lamp (MIL) is activated after a concern is detected on 2 consecutive drive cycles.

Catalyst Efficiency Monitor

Integrated Air Fuel Catalyst Monitor

The integrated air fuel catalyst monitor is an on board strategy designed to monitor the oxygen storage capacity of the catalyst after a deceleration fuel shut off (DFSO) event. The monitor determines the amount of fuel needed to drive the catalyst to a rich condition when starting from an oxygen saturated, lean condition. The monitor is a measure of how much fuel is required to force the catalyst from a lean to a rich condition. The monitor runs during fuel reactivation following a DFSO event. The monitor completes after a calibrated number of DFSO monitoring events have occurred.

2016 Powertrain Control/Emissions Diagnosis, Gasoline Engines, 3/2015