Idle Learn Procedure
The PCM can compensate for minor variations within the fuel system through the block learn and fuel integrator systems. The fuel integrator monitors the oxygen sensor output voltage, adding or subtracting fuel to drive the mixture rich or lean as needed to reach the ideal air fuel ratio of 14.7:1. The integrator values may be read with a scan tool; the display will range from 0-255 and should center on 128 if the oxygen sensor is seeing a 14.7:1 mixture.
The temporary nature of the integrator's control is expanded by the block learn function. The name is derived from the fact that the entire engine operating range (load vs. rpm) is divided into 16 sections or blocks. Within each memory block is stored the correct fuel delivery value for that combination of load and engine speed. Once the operating range enters a certain block, that stored value controls the fuel delivery unless the integrator steps in to change it. If changes are made by the integrator, the new value is memorized and stored within the block. As the block learn makes the correction, the integrator correction will be reduced until the integrator returns to 128; the block learn then controls the fuel delivery with the new value.
The next time the engine operates within the block's range, the new value will be used. The block learn data can also be read by a scan tool; the range is the same as the integrator and should also center on 128. In this way, the systems can compensate for engine wear, small air or vacuum leaks or reduced combustion.
Any time the battery is disconnected, the block learn values are lost and must be relearned by the PCM. This loss of corrected values may be noticed as a significant change in driveability. To re-teach the system, make certain the engine is fully warmed up. Drive the vehicle at part throttle using moderate acceleration and idle until normal performance is felt.
The vehicle's Powertrain Control Module (PCM), is a powerful on-board computer that controls most powertrain related functions, hence its name. Earlier versions were often called the Engine Control Module (ECM) but as the computers have become more advanced and, as more and more demands have been placed on them to control more driveline functions, the computers have come to be called Powertrain Control Modules, more accurately reflecting its increased role in vehicle operations.
The PCM in your W-Body vehicle is located underhood, in front of the right strut tower near the engine coolant reservoir. It is the control center for the fuel injection system and constantly looks at the information from various sensors and it controls the systems that affect vehicle performance. It controls the fuel metering system, automatic transaxle shifting, the engine's ignition timing, and also contains a powerful on-board diagnostic system for powertrain functions.
The PCM constantly looks at the information from various sensors and controls the systems that affect vehicle performance. The PCM also performs the diagnostic function of the system. It can recognize operational problems, alert the driver through the MIL (Malfunction Indicator Lamp, also known as the Service Engine Soon light), and store Diagnostic Trouble Codes (DTCs) which identify the problem areas to aid the technician in making repairs. A qualified technician with a piece of equipment called a scan tool, can connect into the system and read the data stream, getting real-time information on the engine's operation. In addition, the technician can interrogate the system and retrieve any DTCs to aid in diagnosing many driveability problems.
For service (replacement parts), the PCM consists of two parts:
The PCM supplies either 5 or 12 volts to power various sensors or switches. This is done through resistances in the PCM which are so high in value that a test light will not light when connected to the circuit. In some cases, even an ordinary shop voltmeter will not give an accurate reading because its resistance is too low. Therefore, a digital voltmeter with at least 10 megaohms input resistance is required to ensure accurate voltage readings.
The PCM controls output circuits such as the fuel injectors, Idle Air Control (IAC), cooling fan relays, etc., by controlling either the ground or the power feed circuit through transistors or a device called a Driver.
The Electrically Erasable Programmable Read Only Memory (EEPROM) is a permanent memory that is physically soldered within the PCM. The EEPROM contains program and calibration information that the PCM needs to control powertrain operation.
Unlike the Programmable Read Only Memory (PROM) used in certain past applications, the EEPROM is not replaceable. If the PCM is replaced, the new PCM will need to be programmed. This can only be done at a GM dealership. A scan tool such as GM's Tech 1®, or Tech 2®, containing the correct program and calibration for the vehicle is required to program the replacement PCM.
Removal & Installation
Service of the PCM should normally consist of either replacement of the PCM or EEPROM programming. A replacement PCM should first be checked to verify it is the correct part. If so, remove the faulty PCM and install a new service PCM.
- Disconnect the negative battery cable.
- Remove the engine coolant reservoir, if required, for access to the PCM.
- On the Intrigue, remove the left strut brace and disconnect the air duct for access to the PCM.
- Remove the PCM attaching hardware and detach the electrical connectors.
- Remove the PCM from the engine compartment.
- Remove the PCM access cover and remove the Knock Sensor (KS) module. This module must be transferred to the replacement PCM.
- Installation is a reverse of the removal process.
- Take great care handling the multi-pin electrical connectors as they are easily damaged.
- Reprogram the new PCM's EEPROM, using a Tech 1® or equivalent scan tool and the latest available software, and also initiate the PCM Replacement/Programming Crankshaft Position Sensor Variation Learn Procedure. In all likelihood, the vehicle must be towed to a dealer or repair shop containing the suitable equipment for this service.