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303-14-18 Powertrain Control Management 303-14-18 DESCRIPTION AND OPERATION (Continued) nitrogen oxide (NOX) gasses, while providing Module Programming excellent fuel economy, optimal power and performance. The system regulates emissions and Special Tool(s) fuel economy by controlling the air-fuel ratio at the Worldwide Diagnostic System optimum level during different driving conditions. (WDS) Within the closed loop system, deviations from the — optimal air-fuel ratio are measured. The PCM monitors the signal from the HEGO sensor, then adjusts fuel-air mixture to maintain the correct ratio. oxygen content in the exhaust with a HEGO sensor. The oxygen content of the exhaust is a measure of Principles of Operation the air-fuel ratio being provided to the engine. Where PCM modules must be programmed as part of the the air-fuel ratio deviates from the stoichiometric point repair procedure. If this procedure is not followed the of 14.64:1, the sensor voltage output changes module will not function correctly and may set a sharply. The PCM evaluates the change and adjusts number of DTCs, including P1639, which indicate that the injector pulse width to maintain the air fuel ratio some necessary data has not been programmed into within the stoichiometric point. In Closed Loop Mode, the module. the air-fuel ratio is kept at the optimum for all driving PCMs should not be exchanged between vehicles. In conditions. most cases the parameter values or settings are This precise control of the fuel-air ratio allows a unique to that vehicle, and if not set correctly will catalytic converter to be used in the exhaust system cause malfunctions or faults. to burn-up the harmful particles and maintain the WDS will automatically attempt to retrieve the module lowest exhaust emissions. configuration information from all modules, and from a After the HEGO has reached operating temperature, backup location in the PCM when the vehicle ID is the PCM selects Closed Loop Mode during closed carried out. If the module and the PCM do not contain throttle or part throttle operation. correct information the diagnostic tool will display a list Closed Throttle Mode of items that you will need to manually configure. The diagnostic tool will program the module based on the Closed Throttle Mode occurs whenever there is no data you enter. demand on the throttle. This occurs during idle, There are three different methods that are used for coasting and deceleration. The PCM is able to detect module programming: a closed throttle condition by monitoring the signal from the Throttle Position Sensor (TP) <TPS>. programmable module installation (PMI) The PCM controls idle speed, injector pulse width and module reprogramming ignition timing in Closed Throttle Mode to maintain the programmable parameters correct air-fuel ratio. Some modules do not support all three methods. Under periods of prolonged idle, the PCM will exit Programmable Module Installation (PMI) closed loop mode and hold the mixture slightly richer than the stoichiometric point to enhance idle quality. The programmable module installation (PMI) method During deceleration at engine speeds above is used when a new PCM module is installed on the approximately 2,000 RPM, the injectors are shut off. vehicle. The diagnostic tool automatically obtains any At engine speeds below 2,000 RPM, the fuel injectors available module option content information for the old are re-enabled. PCM during the vehicle ID routine that runs when the diagnostic tool is initially connected to the vehicle. It is Powertrain Control Hardware important that you connect WDS to the vehicle and allow it to identify the vehicle and obtain configuration Powertrain Control Module data prior to removing the old PCM. The centre of the PCM system is a microprocessor Module Programming controlled Powertrain Control Module (PCM). Depending on model, the PCM has 92 or 122 Calibration update is used to install a new calibration electrical connector pins through which it receives and strategy into a module. The updates are usually input from sensors and other electronic components. issued to fix a concern in the module software and Based on information received and programmed into would normally be addressed by another technical its memory, the PCM generates output signals to service bulletin (TSB). control the engine and transmission through various relays, solenoids and actuators. G98122 en |