Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET2003TRAILBLAZER 4WD L6-4.2L VIN SREPAIR AND DIAGNOSISRELAYS AND MODULESRELAYS AND MODULES - POWERTRAIN MANAGEMENTRELAYS AND MODULES - COMPUTERS AND CONTROL SYSTEMSENGINE CONTROL MODULEDESCRIPTION AND OPERATION
2003 Chevrolet TrailBlazer 4WD L6-4.2L VIN S
Engine Control Module: Description and Operation
2003 Chevrolet TrailBlazer 4WD L6-4.2L VIN SSECTION Description and Operation
POWERTRAIN CONTROL MODULE (PCM)
The PCM verifies that the password received from the theft deterrent control module via the serial data circuit is correct. The PCM can learn only one fuel continue password. If the fuel continue password is correct, the PCM enables the starting and fuel delivery systems.
The PCM disables the starting and fuel delivery systems if any of the following conditions occur:
- The fuel continue password is incorrect.
- The fuel disable password is sent by the theft deterrent control module.
- No passwords are received - there is no communication with the theft deterrent control module.
The powertrain control module (PCM) contains the remainder of the logic of the theft deterrent system. If a class 2 message containing a valid password is received from the BCM, the PCM will continue to allow the fuel injectors to operate. The PCM will allow the fuel injectors to operate until it decides there is no valid password coming from the BCM. If the PCM does not receive a class 2 message, or receives a class 2 message with an incorrect password, the engine will crank and will not run or will start and stall immediately.
The PCM controls all ignition system functions, and constantly corrects the spark timing. The PCM monitors information from various sensor inputs that include the following:
- The throttle position (TP) sensor
- The engine coolant temperature (ECT) sensor
- The mass air flow (MAF) sensor
- The intake air temperature (IAT) sensor
- The vehicle speed sensor (VSS)
- The transmission gear position or range information sensors
- The engine knock sensors (KS)
The PCM verifies that the password received from the theft deterrent control module via the serial data circuit is correct. The PCM can learn only one fuel continue password. If the fuel continue password is correct, the PCM enables the starting and fuel delivery systems.
The PCM disables the starting and fuel delivery systems if any of the following conditions occur:
- The fuel continue password is incorrect.
- The fuel disable password is sent by the theft deterrent control module.
- No passwords are received - there is no communication with the theft deterrent control module.
The powertrain control module (PCM) contains the remainder of the logic of the theft deterrent system. If a class 2 message containing a valid password is received from the BCM, the PCM will continue to allow the fuel injectors to operate. The PCM will allow the fuel injectors to operate until it decides there is no valid password coming from the BCM. If the PCM does not receive a class 2 message, or receives a class 2 message with an incorrect password, the engine will crank and will not run or will start and stall immediately.
The PCM controls all ignition system functions, and constantly corrects the spark timing. The PCM monitors information from various sensor inputs that include the following:
- The throttle position (TP) sensor
- The engine coolant temperature (ECT) sensor
- The mass air flow (MAF) sensor
- The intake air temperature (IAT) sensor
- The vehicle speed sensor (VSS)
- The transmission gear position or range information sensors
- The engine knock sensors (KS)
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.