Powertrain Control Software
POWERTRAIN CONTROL SOFTWAREBrake 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 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. 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.
Computer Controlled Shutdown
NOTE: The injectors and ignition coils are powered through a dedicated coil/injector relay so that the engine stops running when the ignition is turned to the OFF position.
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 and allows for increased rear heated oxygen sensor (HO2S) concern detection.
Engine RPM Limiter
The PCM disables some or all of the fuel injectors whenever an engine RPM or vehicle over speed condition is detected. The purpose of the engine RPM or vehicle speed limiter is to prevent damage to the powertrain. The vehicle exhibits a rough running engine condition, and the PCM stores a diagnostic trouble code (DTC) P0219. Once the engine returns to the normal operating mode. No repair is required. However, the technician should clear the 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
The fail-safe cooling strategy is activated by the PCM only in the event that 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 cylinder head temperature (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 may 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 period of time when an overheat condition exists.
The engine temperature is controlled by varying and alternating the number of disabled fuel injectors. This allows all cylinders to cool. When the fuel injectors are disabled, their respective cylinders work as air pumps, and this air is used to cool the cylinders.
On the hybrid vehicle, the PCM provides a fail-safe cooling status information to the instrument cluster (IC) through the controller area network (CAN). The PCM sends a CAN message signal to the cluster indicating what fail-safe cooling mode the vehicle is in. There are three levels of this message; normal operating mode, fail-safe mode one, and fail-safe mode 2. The cluster turns the red temperature indicator off if normal operating mode is received, turns the red temperature indicator on if it receives a fail-safe mode 1 message, and it flashes the red temperature indicator if it receives a fail-safe mode 2 message. During fail-safe mode 1 the PCM sets DTC P1285 and during fail-safe mode 2 the PCM sets DTC P1299.
NOTE:The IC red temperature indicator is also used by the motor electronics cooling system loop and may be illuminated by an over temperature condition in that subsystem. The motor electronics cooling system loop includes the generator, DC/DC converter, and the traction motor. The motor electronics cooling system loop also contains a motor electronic coolant temperature (MECT) sensor and motor electronics coolant system (MECS) pump to circulate the coolant. For additional information on the MECT sensor and the MECS pump, refer to Engine Control Components.
Failure Mode Effects Management
Failure mode effects management (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 perceived to be out-of-limits by the PCM, an alternative strategy is initiated. The PCM substitutes a fixed value and continues to monitor the incorrect sensor input. If the suspect sensor operates within limits, the PCM returns to the normal engine operational strategy.
All FMEM sensors display a sequence error message on the scan tool. The message may or may not be followed by key ON engine OFF (KOEO) or continuous memory DTCs when attempting key ON engine running (KOER) self-test mode.
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 without removing the PCM from the vehicle. If a software change is required to the PCM, the module no longer needs to be replaced, but can be reprogrammed using a scan tool.
Fuel Trim
Short Term Fuel Trim
If the heated oxygen sensors (HO2S) are warmed up and the PCM determines the engine can operate near stoichiometric air/fuel ratio (14.7:1 for gasoline), the PCM goes into closed loop fuel control mode. Since an oxygen sensor can only indicate rich or lean, the fuel control strategy must constantly adjust the desired air/fuel ratio rich and lean to get the oxygen sensor to switch around the stoichiometric point. If the times between switches are the same, then the system is actually operating at stoichiometry. The desired air/fuel control parameter is called short term fuel trim SHRTFT1) where stoichiometry 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 +/- 25%. Sometimes the calibration can run the system slightly lean or rich of stoichiometry. 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 NOx.
Values for SHRTFT1 may change a great deal on a scan tool when the engine is operated at different RPM and load points. This is because SHRTFT1 reacts to fuel delivery variability that can change 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, the short term fuel trim corrections can be learned by the PCM as long term fuel trim (LONGFT1) corrections. These corrections are stored in keep alive memory (KAM) in tables that are referenced by engine speed and load. 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, just like short term fuel trim, however it is not a single parameter. There is a separate long term fuel trim value that is used for each RPM/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 or oxygenates). When viewing the LONGFT1 PID, the values may change a great deal as the engine is operated at different RPM and load points. The LONGFT1 PID displays the long term fuel trim correction that is currently being used at that RPM/load point.
High Speed Controller Area Network (CAN)
The high speed CAN is based on SAE J2284, ISO-11898 and 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 two or more electronic modules or nodes to communicate with each other. This communication network operates at 500 kilobytes per second (kb/sec) and allows the electronic modules to share their information messages.
Included in these messages is diagnostic data that is output over the CAN high (+) and CAN low (-) lines to the data link connector (DLC). The diagnostic data such as self-test DTCs or parameter identifiers (PIDs) can be accessed with the scan tool. Information on scan tool equipment is described in Diagnostic Methods, Diagnostic Methods.
International Standards Organization (ISO) 14229 Diagnostic Trouble Code (DTC) Descriptions
The ISO 14229 is a global, diagnostic communication standard. The ISO 14229 is a set of standard diagnostic messages that can be used to diagnose any vehicle module in use and at the assembly plant. The ISO 14229 is similar to the Society of Automotive Engineers (SAE) J2190 diagnostic communication standard that was used by all Original Equipment Manufacturers (OEMs) for previous communication protocols, like J1850 standard corporate protocol (SCP).
The ISO 14229 changes the way PIDs, DTCs, and output state control (OSC) is processed internally in the PCM and in the scan tool software. Most of the changes make data transfer between electronic modules more efficient, and the amount and type of information that is available for each DTC. This information may be helpful in diagnosing driveability concerns.
DTC Structure
Like all digital signals, DTCs are sent to the scan tool as a series of 1s and 0s. Each DTC is made up of two data bytes which each consist of eight bits that can be set to 1 or 0. The data is decoded by the scan tool to display each set of four bits as a hexadecimal number (0 to F) in order to display the DTCs in the conventional format. For example, P0420 Catalyst System Efficiency Below Threshold (Bank 1).
The table below shows how to decode the bits into hex digits.
The first four bits of a DTC do not convert directly into hex digits. The conversion into different types of DTCs (P, B, C and U) is defined by SAE J2012. This standard contains DTC definitions and formats.
ISO 14229 sends two additional bytes of information with each DTC, a failure type byte and a status byte.
All ISO 14229 DTCs are four bytes long instead of three or two bytes long. Additionally, the status byte for ISO 14229 DTCs is defined differently than the status byte for previous applications with three byte DTCs.
Failure Type Byte
The failure type byte is designed to describe the specific failure associated with the basic DTC. For example, a failure type byte of 1C means circuit voltage out of range, 73 means actuator stuck closed. When combined with a basic component DTC, it allows one basic DTC to describe many types of failures.
For example, P0110:1C-AF means intake air temperature (IAT) sensor circuit voltage out of range. The base DTC, P0110, means intake air temperature sensor circuit, while the failure type byte 1C means circuit voltage out of range. This DTC structure was designed to allow manufacturers to more precisely identify different kinds of faults without always having to define new DTC numbers.
The PCM does not use failure type bytes and always sends a failure type byte of 00 (no sub type information). This is because OBD-II regulations require manufacturers to use two byte DTCs for generic scan tool communications. Additionally, the OBD-II regulations require the two byte DTCs to be very specific, so there is no additional information that the failure type byte could provide.
A list of failure type bytes is defined by SAE J2012 but is not described here because the PCM does not use the failure type byte.
Status Byte
The status byte is designed to provide additional information about the DTC, such as when the DTC failed, when the DTC was last evaluated, and if any warning indication has been requested. Each of the eight bits in the status byte has a precise meaning that is defined in ISO 14229.
The protocol is that bit seven is the most significant and left most bit, while bit zero is the least significant and right most bit.
DTC Status Bit Definitions
Refer to the following status bit descriptions:
Bit 7
- 0 - The ECU is not requesting warning indicator to be active
- 1 - The ECU is requesting warning indicator to be active
Bit 6
- 0 - The DTC test completed this monitoring cycle
- 1 - The DTC test has not completed this monitoring cycle
Bit 5
- 0 - The DTC test has not failed since last code clear
- 1 - The DTC test failed at least once since last code clear
Bit 4
- 0 - The DTC test completed since the last code clear
- 1 - The DTC test has not completed since the last code clear
Bit 3
- 0 - The DTC is not confirmed at the time of the request
- 1 - The DTC is confirmed at the time of the request
Bit 2
- 0 - The DTC test completed and was not failed on the current or previous monitoring cycle
- 1 - The DTC test failed on the current or previous monitoring cycle
Bit 1
- 0 - The DTC test has not failed on the current monitoring cycle
- 1 - The DTC test failed on the current monitoring cycle
Bit 0
- 0 - The DTC is not failed at the time of request
- 1 - The DTC is failed at the time of request
For DTCs that illuminate the malfunction indicator lamp (MIL), a confirmed DTC means the PCM has stored a DTC and has illuminated the MIL. If the fault has corrected itself, the MIL may no longer be illuminated but the DTC still shows a confirmed status for 40 warm up cycles at which time the DTC is erased.
For DTCs that do not illuminate the MIL, a confirmed DTC means the PCM has stored a DTC. If the fault has corrected itself, the DTC still shows a confirmed status for 40 warm up cycles at which time the DTC is erased.
To determine if a test has completed and passed, for example, after a repair, information can be combined from two bits as follows:
If bit 6 is 0 (the DTC test completed this monitoring cycle), and bit 1 is 0 (the DTC test has not failed on the current monitoring cycle), then the DTC has been evaluated at least once this drive cycle and was a pass.
If bit 6 is 0 (the DTC test completed this monitoring cycle) and bit 0 is 0 (the DTC test is not failed at the time of request), then the most recent test result for that DTC was a pass.
The status byte bits can be decoded as a two digit hexadecimal number, and can be displayed as the last two digits of the DTC, for example for DTC P0110:1C-AF, AF represents the status byte info.
Multiplexing
The increased number of modules on the vehicle necessitates a more efficient method of communication. Multiplexing is a method of designating a system for sending two or more signals simultaneously over a single circuit. In an automotive application, multiplexing is used to allow two or more electronic modules to communicate simultaneously over a single media. Typically this media is a twisted pair of wires. The information or messages that can be communicated on these wires consists of commands, mode status, or data. The advantage of using multiplexing is to reduce the weight of the vehicle by reducing the number of redundant components and electrical wiring.
Multiplexing Implementation
The multiplexing can be implemented by using a communication language protocol such as CAN. Vehicle network protocols such as CAN allow module-to-module communication to become possible. This communication allows several modules to share information within the vehicle network. The hybrid vehicle uses a high-speed CAN protocol for its powertrain communication. For more information about the entire communication network, refer to Information Bus, Module Communications.
Permanent Diagnostic Trouble Code (DTC)
The software stores a permanent DTC in non-volatile random access memory (NVRAM) whenever a DTC is set and the MIL has been illuminated. Permanent DTCs can only be cleared by the module strategy itself. After a permanent DTC is stored, three consecutive test passed monitoring cycles must complete before the permanent DTC can be erased. The PCM clears the permanent DTCs after one monitoring cycle if a request to clear DTCs is sent by the scan tool and the test subsequently runs and passes. A permanent DTC cannot be erased by clearing the keep alive memory (KAM). The intended use of the permanent DTC is to prevent vehicles from passing an in-use inspection simply by disconnecting the battery or clearing the DTCs with a scan tool prior to the inspection. The presence of the permanent DTCs at an inspection without the MIL illuminated is an indication that a correct repair was not verified by the on-board monitoring system.
Vehicle Speed Functional Overview
The hybrid vehicle uses three methods to calculate vehicle speed.
Vehicle Speed From The Anti-Lock Brake System (ABS) Module
The ABS module calculates wheel speed from the front two wheel speed sensors and sends this information to the PCM through the communication network.
Vehicle Speed From The Transaxle Control Module (TCM)
The TCM calculates traction motor speed from the traction motor shaft speed sensor and combines it with (PCM stored) tire size and axle ratio data to determine vehicle speed. This calculation is then sent to the PCM over the communication network.
Vehicle Speed From Engine And Generator Speed
The TCM calculates generator speed from the generator shaft speed sensor and sends this information to the PCM. The PCM combines input information from the generator speed and engine speed along with tire size and gear ratio to calculate a vehicle speed.
The PCM strategy then cross-checks all the inputs to determine if they agree with one another.