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POWERTRAIN CONTROL SOFTWAREAdaptive Airflow
Some vehicles equipped with electronic throttle control (ETC) have an adaptive airflow strategy that allows the powertrain control module (PCM) to correct for changes in the airflow. During idle, the PCM monitors the throttle angle and airflow. If the airflow is determined to be less than expected, the PCM adjusts the throttle angle to compensate.
The PCM only learns the adaptive airflow when the vehicle is at idle and normal operating temperature and the airflow is less than a calibrated limit. Whenever the battery is disconnected or the keep alive memory (KAM) is reset, it is necessary for the PCM to learn the new value and not use the default value. For additional information on a KAM reset, refer to Diagnostic Methods, Resetting The Keep Alive Memory (KAM). Resetting The Keep Alive Memory (KAM)
Brake Over Accelerator
NOTE: On some vehicles, for off road use the brake over accelerator feature can be disabled along with the electronic stability control system by pressing and holding the traction control OFF button for 5 seconds. (Mustang and Raptor)
The brake over accelerator feature was initially launched on the Fiesta. The F-Series Super Duty with the 6.7L diesel engine will have this feature enabled on late build vehicles or with any calibration update on early build vehicles. All other vehicles with electronic throttle control will get this feature as a running change.
The F-Series Super Duty with the 6.7L diesel engine and the Fiesta do not have PIDs associated with the brake over accelerator feature. All other vehicles will have PIDs that will be viewable with the vehicle communication module (VCM) and integrated diagnostic system (IDS) software with appropriate hardware or an equivalent scan tool. This feature is controlled by the PCM. All system and diagnostic information will be located.
The brake over accelerator feature may not be active during low speed operating conditions. This enables unique drive maneuvers such as trailer tow, boat launch and retrieval or operation in hilly environments where the operator may require the application of both the accelerator pedal and the brake pedal during low speed maneuvering. The brake over accelerator feature will be active at speeds greater than 16 km/h (10 mph).
In the event the accelerator pedal becomes entrapped, such as by an object lodging the pedal, the brake over accelerator feature will reduce engine power when the brake pedal is applied.
The hybrid vehicles achieve a result similar to the brake over accelerator feature by reducing power if the brakes are applied while the accelerator pedal is pressed.
Operators that rest a foot on the brake pedal when also applying the accelerator pedal may activate the brake over accelerator feature. The brake activation is detected by the PCM from the electrical brake switch. In addition to brake over accelerator comments, the customer may bring the vehicle in for repair to address concerns such as a hesitation/stumble or a lack/loss of power. In the event of a hesitation/stumble or a lack/loss of power concern, carry out normal vehicle diagnostics for the appropriate symptom code. On applicable vehicles, if the brake over accelerator feature is suspect, the BRKOVR_ACTION, BRKOVRD_POSS and DIST_BRKOVRD PIDs will display a brake over accelerator event occurred.
In the event the brake over accelerator feature is suspected as the cause of the customer concern, explain to the customer the details of the override system as described above. Additionally, make sure the customer is aware that resting a foot on the brake pedal while driving may cause the activation of this feature. This also results in activation of the brake lights on the vehicle while driving. For additional information refer to the Owners Literature.
Check Fuel Cap Indicator
The check fuel cap indicator is a communications network message sent by the PCM. The PCM sends the message to illuminate the lamp when the strategy determines there is a concern in the EVAP system due to the fuel filler cap or capless fuel tank filler pipe not being sealed correctly. This is detected by the inability to pull vacuum in the fuel tank after a fueling event.
Computer Controlled Shutdown
The PCM controls the PCM power relay when the ignition is turned to the ON or START position, by grounding the PCM relay control (PCMRC) circuit. After the ignition is turned to the OFF, ACC or LOCK position, the PCM stays powered up until the correct engine shutdown occurs.
The ignition switch position run (ISP-R) and the injector power monitor (INJPWRM) circuits provide the ignition state input to the PCM. Based on the ISP-R and INJPWRM signals the PCM determines when to power down the PCM power relay.
Deceleration Fuel Shut-Off (DFSO)
During a DFSO event the PCM disables the fuel injectors. A DFSO event occurs during closed-throttle, deceleration; similar to exiting a freeway. This strategy improves fuel economy, allows for increased rear heated oxygen sensor (HO2S) concern detection, and allows for misfire profile correction learning.
Engine Fluid Temperature Management
The engine fluid temperature management can be activated when high temperature or high load conditions take place. When the engine fluid temperature management is activated, the PCM sends a controller area network (CAN) message to the instrument cluster (IC) or instrument panel cluster (IPC). The IC (IPC) then displays a power reduced to lower temp message. The engine coolant temperature gauge needle moves toward the H (hot) zone. In order to manage the engine's fluid temperatures, the PCM starts to reduce engine power and vehicle speed. The air conditioning may cycle ON and OFF to protect overheating of the engine.
Engine RPM Limiter
The PCM disables some or all of the fuel injectors whenever an engine RPM over speed condition is detected. The purpose of the engine RPM limiter is to prevent damage to the powertrain. Once the driver reduces the excessive engine speed, the engine returns to the normal operating mode. No repair is required. However, the technician should clear the diagnostic trouble codes (DTCs) and inform the customer of the reason for the DTC.
Excessive wheel slippage may be caused by sand, gravel, rain, mud, snow, ice, or excessive and sudden increase in RPM while in NEUTRAL or while driving.
Fail-Safe Cooling Strategy
NOTE: Not all vehicles with a cylinder head temperature (CHT) sensor have the fail-safe cooling strategy.
The fail-safe cooling strategy is only activated by the PCM when an overheating condition has been identified. This strategy provides engine temperature control when the cylinder head temperature exceeds certain limits. The cylinder head temperature is measured by the CHT sensor. For additional information about the CHT sensor, refer to Engine Control Components.
A cooling system failure, such as low coolant or coolant loss, could cause an overheating condition. As a result, damage to major engine components could occur. Along with a CHT sensor, the fail-safe cooling strategy is used to prevent damage by allowing air cooling of the engine. This strategy allows the vehicle to be driven safely for a short time with some loss of performance when an overheat condition exists.
Engine temperature is controlled by alternating the number of disabled fuel injectors, allowing all cylinders to cool. When the fuel injectors are disabled, the respective cylinders work as air pumps, and this air is used to cool the cylinders. The more fuel injectors that are disabled, the cooler the engine runs, but the engine has less power.
A wide open throttle (WOT) delay is incorporated if the cylinder head temperature is exceeded during WOT operation. At WOT, the injectors function for a limited amount of time allowing the customer to complete a passing maneuver.
Before injectors are disabled, the fail-safe cooling strategy alerts the customer to a cooling system problem by moving the IC or IPC temperature gauge to the H (hot) zone and setting DTC P1285. Depending on the vehicle, other indicators such as an audible chime or warning lamp, can be used to alert the customer of fail-safe cooling. If overheating continues, the strategy begins to disable the fuel injectors, DTC P1299 is stored in the PCM memory, and a malfunction indicator lamp (MIL) illuminates. If the overheating condition continues and a critical temperature is reached, all fuel injectors are turned OFF and the engine is disabled.
Failure Mode Effects Management (FMEM)
The FMEM is an alternate system strategy in the PCM designed to maintain engine operation if one or more sensor inputs fail.
When a sensor input is determined to be out-of-limits by the PCM, an alternative strategy is initiated. The PCM substitutes a fixed value for the incorrect input and continues to monitor the suspect sensor input. If the suspect sensor begins to operate within limits, the PCM returns to the normal engine operational strategy.
Flash Electrically Erasable Programmable Read Only Memory (EEPROM)
The flash EEPROM is an integrated circuit within the PCM. This integrated circuit contains the software code required by the PCM to control the powertrain. One feature of the EEPROM is that it can be electrically erased and then reprogrammed through the data link connector (DLC) without removing the PCM from the vehicle.
Fuel Level Input (FLI)
The FLI is a communications network message. Most vehicle applications use a potentiometer type FLI sensor connected to a float in the fuel pump (FP) assembly to determine fuel level.
Fuel Trim
Short Term Fuel Trim
If the oxygen sensors are warmed up and the PCM determines the engine can operate near stoichiometric air/fuel ratio (14.7:1 for gasoline), the PCM enters closed loop fuel control mode. Since an oxygen sensor can only indicate rich or lean, the fuel control strategy continuously adjusts the desired air/fuel ratio between rich and lean causing the oxygen sensor to switch around the stoichiometric point. If the time between rich and lean switches are the same, then the system is actually operating at stoichiometric. The desired air/fuel control parameter is called short term fuel trim (SHRTFT1 and 2) where stoichiometric is represented by 0%. Richer (more fuel) is represented by a positive number and leaner (less fuel) is represented by a negative number. Normal operating range for short term fuel trim is between -25% and 25%. Some calibrations have time between switches and short term fuel trim excursions that are not equal. These unequal excursions run the system slightly lean or rich of stoichiometric. This practice is referred to as using bias. For example, the fuel system can be biased slightly rich during closed loop fuel to help reduce nitrogen oxides (NOx).
Values for SHRTFT1 and 2 may change significantly on a scan tool as the engine is operated at different RPM and load points. This is because SHRTFT1 and 2 react to fuel delivery variability that changes as a function of engine RPM and load. Short term fuel trim values are not retained after the engine is turned OFF.
Long Term Fuel Trim
While the engine is operating in closed loop fuel control, the short term fuel trim corrections are learned by the PCM as long term fuel trim (LONGFT1 and 2) corrections. These corrections are stored in the keep alive memory (KAM) fuel trim tables. Fuel trim tables are based on engine speed and load and by bank for engines with 2 heated oxygen sensor (HO2S) forward of the catalyst. Learning the corrections in KAM improves both open loop and closed loop air fuel ratio control. Advantages include:
- Short term fuel trim does not have to generate new corrections each time the engine goes into closed loop.
- Long term fuel trim corrections can be used both while in open loop and closed loop modes.
Long term fuel trim is represented as a percentage, similar to the short term fuel trim, however it is not a single parameter. A separate long term fuel trim value is used for each RPM and load point of engine operation. Long term fuel trim corrections may change depending on the operating conditions of the engine (RPM and load), ambient air temperature, and fuel quality (% alcohol, oxygenates). When viewing the LONGFT1/2 PID(s), the values may change a great deal as the engine is operated at different RPM and load points. The LONGFT1/2 PID(s) display the long term fuel trim correction currently being used at that RPM and load point.
High Speed Controller Area Network (CAN)
The CAN is a serial communication language protocol used to transfer messages (signals) between electronic modules or nodes. Two or more signals can be sent over one CAN circuit allowing 2 or more electronic modules or nodes to communicate with each other. This communication or multiplexing network operates at 500kB/sec (kilobytes per second) and allows the electronic modules to share their information messages.
Included in these messages is diagnostic data that is output over the CAN (+) and CAN (-) lines to the DLC. The PCM connection to the DLC is typically done with a 2-wire, twisted pair cable used for the network interconnection. The diagnostic data such as self-test or PIDs can be accessed with a scan tool. For additional information on scan tool equipment, refer to Diagnostic Methods. Testing and Inspection
Idle Air Trim
Idle air trim is designed to adjust the idle air control (IAC) calibration to correct for wear and aging of components. When the engine conditions meet the learning requirement, the strategy monitors the engine and determines the values required for ideal idle calibration. The idle air trim values are stored in a table for reference. This table is used by the PCM as a correction factor when controlling the idle speed. The table is stored in the KAM and retains the learned values even after the engine is shut OFF. A DTC is set if the idle air trim has reached its learning limits.
Whenever an IAC component is replaced, or a repair affecting idle is carried out, it is recommended the KAM be reset. This is necessary so the idle strategy does not use the previously learned idle air trim values.
To reset the KAM, refer to Diagnostic Methods, Resetting The Keep Alive Memory (KAM). It is important to note that erasing DTCs with a scan tool does not reset the idle air trim table. Resetting The Keep Alive Memory (KAM)
Once the KAM has been reset, the engine must idle for 15 minutes (actual time varies between strategies) to learn new idle air trim values. Idle quality improves as the strategy adapts. Adaptation occurs in 4 separate modes as shown in the following table.
Idle Speed Control Closed Throttle Determination - Applications Without Electronic Throttle Control (ETC)
One of the fundamental criteria for entering RPM control is an indication of closed throttle. Throttle mode is always calculated to the lowest learned throttle position (TP) sensor voltage seen since engine start. This lowest learned value is called ratch, since the software acts like a one-way ratch. The ratch value is displayed as the TPREL PID. The ratch value is relearned after every engine start. Ratch learns the lowest, steady TP sensor voltage seen after the engine starts. In some cases, ratch can learn higher values of throttle position. The time to learn the higher values is significantly longer than the time to learn the lower values. The brakes must also be applied to learn the higher values.
All PCM functions are done using this ratch voltage, including idle speed control. The PCM goes into closed throttle mode when the TP sensor voltage is at the ratch value. An increase in TP sensor voltage, normally less than 0.05 volts, puts the PCM in part throttle mode. Throttle mode can be viewed by looking at the TP MODE PID. With the throttle closed, the PID must read CIT (closed throttle). Slightly corrupt values of ratch can prevent the PCM from entering closed throttle mode. An incorrect part throttle indication at idle prevents entry into closed throttle RPM control, and could result in a high idle. Ratch can be corrupted by a throttle position sensor or a circuit that drops out or is noisy, or by loose/worn throttle plates that close tight during a deceleration and spring back at a normal engine vacuum.