Electronic Throttle Control: Notes
The Electronic Throttle Control (ETC) system uses a strategy that delivers engine shaft torque, based on driver demand, utilizing an electronically controlled throttle body. ETC strategy was developed mainly to improve fuel economy. This is possible by decoupling throttle angle (produces engine torque) from pedal position (driver demand). This allows the powertrain control strategy to optimize fuel control and transmission shift schedules while delivering the requested engine or wheel torque.
Because safety is a major concern with ETC systems, a complex safety monitor strategy (hardware and software) was developed. The monitor system is distributed across two processors: the main powertrain control processor and a monitoring processor called a Quizzer processor.
The primary monitoring function is performed by the Independent Plausibility Check (IPC) software, which resides on the main processor. It is responsible for determining the driver-demanded torque and comparing it to an estimate of the actual torque delivered. If the generated torque exceeds driver demand by specified amount, the IPC takes appropriate mitigating action.
Since the IPC and main controls share the same processor, they are subject to a number of potential, common failure modes. Therefore, the Quizzer processor was added to redundantly monitor selected PCM inputs and to act as an intelligent watchdog and monitor the performance of the IPC and the main processor. If it determines that the IPC function is impaired in any way, it takes appropriate Failure Mode and Effects Management (FMEM) actions.
| Effect | Failure Mode |
| No Effect on Driveability | A loss of redundancy or loss of a non-critical input could result in a fault that does not affect driveability. The Wrench light will turn on, but the throttle control and torque control systems will function normally. |
| RPM Guard w/ Pedal Follower | In this mode, torque control is disabled due to the loss of a critical sensor or PCM fault. The throttle is controlled in pedal-follower mode as a function of the pedal position sensor input only. A maximum allowed RPM is determined based on pedal position (RPM Guard.) If the actual RPM exceeds this limit, spark and fuel are used to bring the RPM below the limit. The wrench light and the MIL are turned on in this mode and an ETC component causal code is set. EGR, VCT, and IMRC outputs are set to default values. |
| RPM Guard w/ Default Throttle | In this mode, the throttle plate control is disabled due to the loss of Throttle Position, the Throttle Plate Position Controller, or other major ETC system fault. A default command is sent to the (e)TPPC, or the H-bridge is disabled. Depending on the fault detected, the throttle plate is controlled or springs to the default (limp home) position. A maximum allowed RPM is determined based on pedal position (RPM Guard.) If the actual RPM exceeds this limit, spark and fuel are used to bring the RPM below the limit. The wrench light and the MIL are turned on in this mode and an ETC component causal code is set. EGR, VCT, and IMRC outputs are set to default values. |
| SLOWE / BOA | This mode is caused by the loss of 1 or 2 pedal position sensor inputs due to sensor, wiring, or PCM faults. For a single sensor fault, driver demand is rate limited based on input from the remaining good sensor. For a dual sensor fault, driver demand is ramped to a fixed pedal position (high idle RPM) and there is no response to the driver input. If the brake pedal is applied for either a single or dual sensor fault, the engine returns to a normal idle RPM. The wrench light is turned on in this mode, and an accelerator pedal sensor causal code is set. |
| PCM Reset (Bosch CY320 or Conti ATIC Quizzer hardware only) |
If a significant processor fault is detected, the monitor will attempt to mitigate the fault by forcing a PCM reset. If the fault clears after the reset, then the vehicle will continue running. If the fault persists, then the monitor will force another reset. This will continue until the fault clears or until the PCM exceeds the maximum number of resets allowed. If this occurs, the PCM is held in reset, and the engine does not run. The maximum number of resets allowed depends on the PCM supplier and the type of fault detected. The wrench light and MIL are turned on in this mode, and the appropriate processor P-code will set. |
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NOTE:
The wrench light illuminates or an ETC message is displayed on the message center immediately. The MIL illuminates after 2 driving cycles.
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