Engine Control Module

Engine Control Module

The engine management system is centered on an ECM. The ECM receives input signals from engine sensors to evaluate engine-operating conditions. In addition, the ECM communicates with other powertrain systems and vehicle systems. The ECM then processes the sensor information and the information received from other systems using programmed software strategies and issues control output signals to the engine and emission control functional systems.

At it's very basic level of control the ECM:
- Takes engine speed and load input signals.
- Applies correction factor inputs and emissions control feedback signals.
- Processes the signals to access pre-programmed software strategies.
- Outputs control signals to the various engine and emission components.
- During this process, the ECM employs diagnostic tests to monitor and report engine management system faults. Faults are stored in ECM memory as codes. Technician access to the DTCs and data is gained through a diagnostic data link.

ECM Control Relay Monitor
After the vehicle ignition has been turned off, the ECM can maintain its own power source by holding on the ECM relay. The ECM turns itself off by releasing this relay. If it has done this but is still operating then there is a fault with the ECM control relay circuit and this is logged.

Main Processor Monitor
At processor initialization, this monitor checks whether the Read Only Memory (ROM) checksum for the sub processor monitor is OK. If the checksums do not agree, a failure judgment is made. The same check is performed for the Random Access Memory (RAM) area for the sub processor monitor. If the checksums do not agree, a failure judgment is made. During ignition on, the main processor mirror checks certain sequence, RAM and ROM calculations with the sub processor. If the mirror checks do not agree, a failure judgment is made.

Sub Processor Monitor
This monitor duplicates various sections of the throttle control functions performed by the sub processor in the main processor and continuously compares the results during ignition on. In case of the sub processor value differing from the main processor value by more than a calibratable amount, a failure judgment is made.

The following functions are checked:
- Throttle target calculation.
- Throttle offset voltage differential failure.
- Throttle target voltage differential failure.
- Throttle valve angle input.
- Pedal angle input.
- Digital servo control.
- Total sub processor calculation.
- Speed control mode cancel.
- Sub processor self-check.

Battery Back Up Monitor
The ECM supply input status is checked after the system initialization with ignition applied. If the supply input is low, the status flag is set. When the ignition is cycled the fault timer is incremented until the timer reaches the calibrated time, thus the fault flag is set.

Processor Communications Monitor
At regular intervals, the validity of all RAM data is checked. Any corruption of RAM data will result in a monitoring failure judgment being made. If all RAM data is verified then a monitoring normal judgment is made.

Engine Control Module Keep Alive Memory Monitor
Every data value stored in the Electrically Erasable Programmable Read Only Memory (EEPROM) is duplicated in a 'mirror' EEPROM location. If all the data values and their mirrors match, a normal judgment is made. If any of the EEPROM data values differ from the value stored in their mirror location then a failure judgment is made and P0603 is logged.