Powertrain Control Module Diagnosis. Chevrolet Metro 1999

For 1990-2009 cars

The powertrain control module (PCM) is an advanced electronic component that requires careful handling and diagnosis. Incorrect testing procedures or the use of incorrect equipment can damage the PCM. The operation of other components can affect the PCM performance.

Service of the PCM consists of the replacement of the PCM. The PCM does not contain serviceable parts. The PCM does not have a programmable read-only memory (PROM) chip. The PCM does not have an erasable programmable read only memory (EPROM) to calibrate. Replace the PCM as a complete assembly if the PCM is faulty.

### Basic Knowledge Of Tools Required

Notice: Lack of basic knowledge of this powertrain when performing diagnostic procedures could result in incorrect diagnostic performance or damage to powertrain components. Do not attempt to diagnose a powertrain problem without this basic knowledge.

A basic understanding of the proper use of hand tools is necessary in order to effectively use this section of the Service Manual.

### Use Of Circuit Testing Tools

Do not use a test lamp for diagnosis of the powertrain control electrical systems unless instructed to by a diagnostic procedure. Use the J 35616 connector adapter kit or an equivalent if the diagnostic procedures call for probing any connectors.

### PCM Service Precautions

Notice: Turn the ignition OFF when installing or removing the PCM connectors and disconnecting or reconnecting the power to the PCM (battery cable, PCM pigtail, PCM fuse, jumper cables, etc.) in order to prevent internal PCM damage.

The powertrain control module (PCM) will withstand the normal current draws associated with vehicle operations. Do not overload any circuit. Do not ground or apply voltage to any PCM circuits unless instructed. Do not apply voltage to any of the PCM circuits if testing for an open or for a short in an electrical circuit. Only test the PCM circuits using the digital J 39200 multimeter or an equivalent. The PCM electrical connectors should remain connected to the PCM during testing.

### Aftermarket Electrical and Vacuum Equipment

Notice: Connect any add-on electrically operated equipment to the vehicle's electrical system at the battery (power and ground) in order to prevent damage to the vehicle.

Notice: Do not attach add-on vacuum operated equipment to this vehicle. The use of add-on vacuum equipment may result in damage to vehicle components or systems.

Add-on electrical and vacuum equipment is any equipment that is connected to the vehicle's electrical or vacuum systems after the vehicle leaves the factory. The vehicle design does not allow for the addition of aftermarket equipment.

Add-on electrical equipment may cause the engine control system to malfunction even if the add-on electrical equipment is correctly installed. Portable telephones radios may also cause engine control system malfunctions even if not connected to the vehicle's electrical system. Before diagnosing any engine control system problem, remove all aftermarket electrical equipment from the vehicle. Diagnosis may proceed in the normal manner after the aftermarket equipment is determined to not be the cause of the malfunction.

### Electrostatic Discharge (ESD) Damage

Notice: In order to prevent possible Electrostatic Discharge damage to the PCM, Do Not touch the connector pins or the soldered components on the circuit board.

Many of the electronic components in the engine control system operate at very low voltages. Electrostatic discharge can damage these electronic components. Less than 100 volts of static electricity can damage some of the electronic components. There are several ways for a person to become statically charged. The usual methods of charging are by friction and by induction. An example of charging by friction is the charging of a person that slides across a car seat. Charging by induction can occur if a person with well-insulated shoes stands near a charged object and momentarily touches a ground. Charges of the same polarity are drained, charging the person with the opposite polarity. Therefore, it is important to use care in handling and testing electronic components in order to avoid electrostatic discharges that can cause electronic component damage.

Important: Do not use a scan tool that displays faulty data. Report the scan tool problem to the manufacturer. Use of a faulty scan tool can result in misdiagnosis and unnecessary parts replacement.

The communication interface with the control module is the data link connector (DLC). The DLC is under the instrument panel to the right of the steering column. The scan tool connects to the DLC. The following are some of the common uses of the scan tool:

• | The identification of stored diagnostic trouble codes (DTCs)

• | The clearing of the DTCs

• | The performance of output control tests

• | The reading of the serial data

### Visual/Physical Underhood Inspection

Perform a careful visual and physical underhood inspection if performing any diagnostic procedure or diagnosing the cause of an emission test failure. This can often lead to the cause of a problem without further steps. Use the following guidelines for performing a visual and physical inspection:

• | Inspect all the vacuum hoses for the following conditions:

- | Any pinched hoses

- | Any cuts

- | Any disconnected hoses

• | Inspect all of the hoses beneath the following components:

- | The air cleaner

- | The A/C compressor

- | The generator

- | Any other engine accessories

• | Inspect all wires in the engine compartment for the following items:

- | Proper connections

- | Burned spots, and chafed spots

- | Pinched wires

- | Contact with sharp edges

- | Contact with hot exhaust manifolds

This visual and physical inspection is very important. The visual and physical inspection must be completed carefully and thoroughly.

### Powertrain OBD System Check

Important: Using the table correctly can reduce diagnosis time and prevent the unnecessary replacement of parts.

The Powertrain OBD System Check is an organized approach for identifying a problem. After the visual inspection is complete, perform the Powertrain OBD System Check. This Powertrain OBD System Check will provide a direction for diagnosis of the following problems:

• | A faulty PCM or an inoperative PCM

• | No serial data

• | An inoperative malfunction indicator lamp (MIL)

• | Any PCM DTCs

• | A rich fuel system or a lean fuel system

• | Customer Complaint Driveability Symptoms

The Powertrain OBD System Check is a master table for driveability diagnosis and for emissions system diagnosis. Use the Powertrain OBD System Check as the starting point for any engine control system diagnosis.

### Diagnostic Procedure Use

Use the diagnostic procedures in this section in order to resolve powertrain related problems. Find the appropriate diagnosis for a problem by using the five basic steps below.

1. Understand the customer's concerns. The technician must understand what the customer's concern is. Failure to understand the customer concern may lead to misdiagnosis or to unnecessary diagnosis. The technician must know if the condition is present at all times, under certain circumstances, or is intermittent. This knowledge will assist the technician in duplicating the problem and in diagnosing the problem. Understanding the customer's concern enables the technician to determine if the condition requires service or is a characteristic of normal vehicle operation. Trying to diagnose a customer concern that is a normal characteristic of vehicle operation may result in unnecessary service.
2. Are the diagnostics that are built into the PCM working correctly? Use the Powertrain OBD System Check. Always begin the diagnostic procedure at this starting point.
3. Are any DTCs set? If the diagnostics identify any DTCs, the Powertrain OBD System Check will direct you to the appropriate table.
4. Is the customer's concern related to a specific powertrain subsystem? If related DTCs are not set, attempt to link the problem to a specific powertrain subsystem. If a specific subsystem can be identified as the cause of the problem, the diagnosis will be quicker and easier.
5. Is the customer's concern powertrain related? Some customer concerns that are caused by other vehicle systems may appear to be powertrain related.

### Using Diagnostic Trouble Code (DTC) Tables

To correctly diagnosing this powertrain, you will need to use the diagnostic procedures in this section or in the other powertrain sections. These diagnostic procedures are mostly in the form of tables. The diagnostic support information will be at the beginning of each DTC table. The support information contains a circuit diagram or an illustration, and a description of the system that is being diagnosed. Reading the diagnostic support information will help you to understand the DTC and the table. The following are descriptions of the diagnostic support information for the DTC tables.

### Circuit Diagram

The circuit diagram of the diagnostic support information will show the circuits and the components that set the DTC. Use this diagram as a reference if the diagnosis requires circuit checks. Use the Engine Controls electrical schematics if the diagnosis requires more detailed circuit information.

### Circuit Description

The circuit description explains the sensor and/or the circuits involved in setting the DTC. The circuit description may also give a brief description of when or how the DTC sets.

### Conditions for Running the DTC

The Conditions for Running the DTC are the conditions necessary for the PCM to test for a failure. These conditions allow checking an input or a system without causing a false failure indication.

### Conditions for Setting the DTC

The Conditions for Setting the DTC are the conditions that the DTC requires in order to set. Failure conditions are only checked for after the running conditions are met. The diagnostic software in the PCM will test for certain faults and set a DTC if a failure is present.

### Action Taken When the DTC Sets

The Action Taken When the DTC Sets are the steps that the PCM takes after the DTC sets. These actions serve 1 of 3 purposes:

• | To alert the driver to the problem

• | To maintain the driveability of the vehicle

• | To prevent the failure from causing any damage to the vehicle

### Conditions For Clearing The MIL / DTC

These conditions must be met in order to turn the MIL off and in order to clear the DTC .

### Diagnostic Aids

Many tables have one result which reads Fault Not Present or Go to Diagnostic Aids. Fault Not Present indicates that the conditions that were present when the DTC set are no longer there. A driveability concern can often be identified by using the Freeze Frame or Failure Records, or the information from the driver. The Diagnostic Aids information may tell to the technician what to look for and where to investigate, in order to diagnose an intermittent failure.

### Test Description

The Test Descriptions describe the reasons for performing the tests and what the tests should determine. This numbered information corresponds to the steps on the table. If you are performing a test, refer to the Test Description for additional information.

### Diagnostic Table

The diagnostic tables are a systematic approach to diagnosing a diagnostic trouble code (DTC).

The table consists of five separate columns:

• | Step

• | Action

• | Value(s)

• | Yes

• | No

The step number indicates which step is being performed. The Action column contains all of the information necessary in order to perform a certain test. The Action cell must always end with a question. The question must lead to a yes or a no answer. The answer to the question determines which column you go to next. The value(s) column will contain any specifications that you are asked to test for. The answer to each test will lead you to the next step, or to the particular action to take. Most boxes will have a "Go to Step" statement. If the block does not have a "Go to Step" statement, the text inside that block will be the last instruction given in the table. The instruction will be a solution, or a Fault Not Present, or a Go to Diagnostic Aids.

Always begin with Step 1 at the top of the table unless there is a Notice or a Caution before the step. Do not skip steps in the table. Taking short cuts often leads to misdiagnosis. If you find a problem, complete the necessary repairs, and verify the repair.

### Reading Diagnostic Trouble Codes Using a Scan Tool

Use a scan tool in order to read the diagnostic trouble codes. Follow the manufacturer's instructions in order to read the DTCs accurately.

### Using Output Controls With a Scan Tool

Important: Do not use the scan tool Output Controls until the vehicle is at normal operating temperatures. The PCM will not respond to a request for Output Controls until the engine coolant temperature is above 80°C (175°F). Failure to wait for normal operating temperatures can result in the incorrect diagnosis of a driveability problem.

The Output Controls are disabled if the PCM stores any DTCs. Clear the DTCs before using the scan tool Output Controls.

The Tech 2 can command the PCM to operate solenoids, valves, motors, and switches. This scan tool function is referred to as the "Output Controls. The Output Controls item is in the Special Functions menu on the Tech 2 scan tool. Limit the operation of a PCM controlled device with the scan tool to a maximum of 10 seconds per test period.

### Clearing Diagnostic Trouble Codes

Important: Clear the DTCs only if the diagnostic procedure directs you to clear the DTCs. The Freeze Frame data which may help diagnose an intermittent fault are erased when you clear the DTCs.

The PCM begins to count the warm-up cycles after the fault that caused the DTC is corrected. The PCM will automatically clear the DTC from memory after the PCM has counted 40 consecutive warm-up cycles without detecting further faults.

Use a scan tool in order to clear the DTCs. In order to clear DTCs, use the scan tool's clear the DTCs or the clear the information function. Follow the instructions that are supplied by the scan tool manufacturer.

### Verifying Vehicle Repair

Verification of the vehicle repair will be more complete for vehicles with the OBD II system diagnostics. After making a repair to the vehicle's engine control system, perform the following steps :

1. Review and record the Freeze Frame data for the DTC that has been diagnosed.The Freeze Frame data is stored for type A or B DTCs only if the malfunction indicator lamp (MIL) has been requested.
2. Clear any DTCs.
3. Operate the vehicle within the conditions that are noted in the Freeze Frame data.
4. Monitor the DTC status information for the specific DTC until the diagnostic test runs.

Following these steps is very important in verifying the repair on OBD II systems. Failure to follow these steps could result in unnecessary repairs or in incorrect repairs.

### Intermittent Malfunction Indicator Lamp

In the case of an intermittent fault, the MIL may illuminate, and turn off after 3 trips. A corresponding diagnostic trouble code will be stored in the memory. Consult the Diagnostic Aids for the diagnostic trouble code. A physical inspection of the applicable sub-system can often resolve the problem.

A diagnostic trouble code that repeatedly illuminates the MIL may indicate an intermittent malfunction.

### Intermittent Malfunctions

There are instances when the MIL indicates that an intermittent fault DTC has cleared. In such instances, good parts are sometimes unnecessarily replaced. Follow the instructions below when using the Diagnostic Tables in order to avoid this problem.

If a malfunction is not an intermittent fault, verify that the sensor, the wires, and the connections are in good condition.

If a malfunction cannot be identified, but the MIL indicates a DTC:

• | Diagnose the malfunction by using the appropriate DTC chart. If the sensor, the wires, and the electrical connections are all in good condition, erase the DTC from the PCM memory. Conduct a test, and determine what DTCs are present when the MIL illuminates. The malfunction is present only if the MIL indicates a DTC again.

• | The first instance of Type B DTCs are stored in the Test Failed Since Code Cleared display, but not in the History display. When the MIL illuminates and a DTC is stored in the History display, a current fault is indicated.

### Notes on System Circuit Inspection

Notice: In order to prevent internal damage to the PCM, the ignition must be OFF when disconnecting or reconnecting the PCM connector.

• | Intermittent malfunctions are often caused by faulty electrical connections or by faulty wiring. Perform a careful check of the suspected circuits for any of the following conditions:

- | Poor mating of the connector halves

- | Electrical terminals that are incorrectly seated in the connector body

- | Incorrectly formed terminals or damaged terminals Carefully repair all connector terminals in malfunctioning circuits in order to increase the contact tension.

- | A poor terminal to wire connection

• | Use a J 39200 digital multimeter with a minimum resistance of more than one megaohm per volt. Do not use other digital multimeters or you may not obtain accurate measurements.

• | When checking the voltage at terminals that are connected to the PCM, connect the negative probe to a body ground.Use a jumper wire in order to connect the positive probe to the connector terminal that is being tested. Incorrect application of the DMM probes may short or damage the sensor or the PCM.

### Wiring Harness Service

Replace the wire harness with the proper replacement. If splicing signal wires into a harness, use a wiring that has high temperature insulation.

Consider the low amperage and the voltage levels the powertrain control systems uses. Make the best possible bond at the splices. Use rosin-core solder in these areas.

Solder-on electrical connectors require the complete replacement of the connector. Splice a new electrical connector into the harness. Replacement electrical connectors and terminals are listed in the Standard Parts Catalog in the Group 8.965.

For wiring repairs, refer to Wiring Repairs .

### Connector Components

In order to prevent shorting between opposite electrical terminals, use care in probing an electrical connector and in replacing electrical terminals. Damage to the engine control components could result.

Always use jumper wires between the electrical connectors when checking circuits.

DO NOT probe through the Weather-Pack seals on the electrical connectors.

The J 35616 adapter kit, or an equivalent, contains an assortment of flexible connectors that are used in order to probe terminals during diagnosis. Use the BT-8616 fuse remover tool, or an equivalent, in order to remove fuses or adapt a fuse holder to a DMM.

Open circuits are often difficult to locate by sight because connectors hide the oxidation or the terminal misalignment. Wiggling an electrical connector on a sensor or in the wiring harness may temporarily correct the open circuit. Oxidized connections or loose connections may cause intermittent problems and must not be over-looked.

Before making any connector repair or terminal repair, verify the connector type and the terminal type. Weather-pack and Com-pack III electrical terminals look similar, but are serviced differently.

### Decimal/Binary/Hexadecimal Conversions

The scan tool displays various vehicle information which aids in repairing the vehicle. Some scan tools will display encoded messages which will aid in determining the type of the concern. This method of encoding involves the use of 2 additional number systems: Binary and Hexadecimal.

The binary number system uses a base of 2. Each of the digits is a 0 or a 1. The number has eight digits and is read from the right to the left. Each digit has a position number. The digit farthest to the right is in the 0 position. The digit farthest to the left is in the 7 position. A 1 in the 0 position indicates the number 1 in the decimal system. Each position to the left is double the previous position and added to any other position values that are marked as a 1.

The hexadecimal system is 16 different alphanumeric characters. The alphanumeric characters are the numbers 0 through 9 and the letters A through F. The hexadecimal system is a common approach scan tool manufacturers use to display binary data and digital data.