ECM
ECM stands for Engine Control Module. On the Pontiac Fiero, the ECM is the computer that controls the engine management system.
The ECM receives information from engine sensors, processes that information, and controls fuel delivery, ignition timing, idle control, emissions functions, and diagnostic trouble code reporting.
Overview
The Fiero ECM is part of the car's electronic fuel injection and engine-control system.
It monitors sensor inputs such as coolant temperature, throttle position, manifold pressure, oxygen sensor voltage, vehicle speed, and engine rpm. Based on those inputs, it controls engine operation through outputs such as the fuel injectors, idle air control valve, electronic spark timing circuit, and emissions-control components.
The ECM also stores and reports Diagnostic trouble codes when it detects certain electrical or operating faults.
ECM functions
The ECM is involved in several major engine-management functions:
- Fuel injector control
- Ignition timing control
- Idle speed control
- Cold-start and warm-up fueling
- Closed-loop fuel control
- Emissions-system control
- Diagnostic trouble code storage
- ALDL data output
Sensor inputs
Common ECM inputs include:
- Coolant temperature sensor
- Throttle position sensor
- Manifold absolute pressure sensor
- Manifold air temperature sensor
- Oxygen sensor
- Vehicle speed sensor
- Distributor reference signal
- Battery voltage
- Park/neutral or gear-related inputs on some applications
ECM outputs
Common ECM-controlled outputs include:
- Fuel injectors
- Idle air control valve
- Electronic spark timing control
- EGR solenoid
- Fuel pump relay control
- Check engine light control
- ALDL diagnostic output
Diagnostic role
The ECM can store trouble codes when it detects certain sensor, circuit, or control problems.
Trouble codes can be read through the ALDL diagnostic connector by placing the ECM into diagnostic mode and counting the flashes of the check engine light.
The first code normally displayed is Code 12, which indicates that the ECM is in diagnostic mode.
PROM and CALPAK
The ECM contains calibration components that are matched to the engine and vehicle configuration.
Important related parts include:
These parts contain calibration or backup-calibration information used by the ECM. Incorrect, damaged, poorly seated, or mismatched calibration parts can cause ECM-related trouble codes or drivability problems.
Related trouble codes include:
Common ECM-related problems
Possible ECM-related problems include:
- Poor ECM grounds
- Poor power supply
- Corroded connectors
- Water intrusion
- Previous wiring modifications
- Damaged PROM or CALPAK
- Incorrect ECM or calibration
- Internal ECM failure
However, ECM failure should not be assumed too quickly. Many apparent ECM problems are actually caused by poor grounds, wiring faults, bad connectors, sensor issues, or charging-system problems.
Grounds and power
The ECM depends on clean power and good grounds. Poor grounds or unstable voltage can cause strange drivability problems, false trouble codes, intermittent stalling, or no-start conditions.
Related topics:
ECM replacement
When replacing an ECM, the replacement unit must be compatible with the vehicle and engine configuration.
In many cases, the original PROM and CALPAK may need to be transferred to the replacement ECM if they are correct and in good condition.
Before replacing the ECM, basic checks should include:
- Verify ECM power and grounds.
- Inspect ECM connectors.
- Check for corrosion or water damage.
- Check battery and charging voltage.
- Check relevant sensor inputs.
- Check for wiring modifications or damage.
- Verify PROM and CALPAK seating if applicable.