General terms of on-board diagnostics system (Chevrolet Captiva 1)

Diagnostics

The word "diagnostics" refers to any on-board test performed by the vehicle's diagnostic control system. Diagnostics are simply test runs of a system or component to determine if it is operating within specifications. There are several diagnostics, as listed below:

• Misfire
• Control Oxygen Sensor (HO2S1)
• Diagnostic oxygen sensor (HO2S2)
• Exhaust Gas Recirculation (EGR)
• Control of neutralizer efficiency

Activation criteria

The term "activation criteria" is a technical term that refers to the conditions required to run a given diagnostic test. Each diagnostic has a specific list of conditions that, when met, trigger the diagnostic.

"Activation criteria" are, in other words, "required conditions".

The activation criteria for each diagnostic are listed on the first page of the diagnostic trouble code description under the heading "Conditions for Setting the DTC". The activation criteria vary from diagnostic to diagnostic and typically include the following:

• Engine speed
• Car speed
• Coolant Temperature (ECT)
• Manifold Absolute Pressure (MAP)
• Barometric pressure (BARO)
• Intake Air Temperature (IAT)
• Throttle Position (TP)
• Strong blowing of the carbon filter
• Fuel supply adjustment
• The air conditioner is on

Drive

Technically, a trip is an ignition on/off cycle in which the activation criteria for a given diagnostic are met to allow it to be run. Unfortunately, the concept is not that simple. A trip is considered valid when all activation criteria for a given diagnostic are met. But, as the activation criteria change from one diagnostic to another, the definition of a trip changes too. Some diagnostics only work when the engine is running, some only work after the engine is running, some require a constant highway speed, others only work at idle or with the torque converter clutch disengaged. Some only work immediately after a cold start.

Thus, a diagnostic is defined as an ignition on/off cycle in which the vehicle was operated in a manner that meets the criteria of that diagnostic, and the diagnostic recognizes that cycle as one trip. However, another diagnostic with a different set of activation criteria (which were not observed) during the trip will not be considered a trip. A trip to a specific diagnostic will not take place if the vehicle does not operate in accordance with all activation criteria.

Diagnostic information

Diagnostic charts and functional tests are designed to find the faulty circuit or component by a logical decision process. The charts are prepared assuming that the vehicle was functioning properly at the time of assembly and that various faults were absent.



Continuous diagnostics of certain control functions are provided. Diagnostic capabilities are supplemented by the diagnostic procedures contained in this manual. The language for communicating the source of the malfunction is the diagnostic trouble code system. When a malfunction is detected by the control module, a diagnostic trouble code is set and the malfunction indicator lamp is illuminated.

Malfunction indicator lamp

The malfunction indicator lamp comes on when a set of conditions required by the on-board diagnostic (OBD) system are strictly met.

Normally, the fault indicator light will light up when the ECM controller detects a diagnostic fault code that strongly affects the vehicle's toxicity.

The fault indicator light is controlled by an executive diagnostic program. The fault indicator light comes on when a diagnostic toxicity test detects a fault. It continues to burn until the system or component passes the same test for three trips without a malfunction in the toxicity control system.

Disabling the Malfunction Indicator Lamp

When the fault indicator light is on, the executive diagnostic program turns it off after three consecutive trips with the result "test passed" for the diagnosis that caused the fault indicator light to turn on. Although the fault indicator light is turned off, the diagnostic fault code is stored in the memory of the ECM controller (both in the status record and in the fault log) until forty (40) heating cycles have been completed without failure.

If the fault indicator light has been activated by a fuel supply adjustment or a diagnostic toxicity control fault code, additional requirements must be met. Additional requirements to those described in the previous paragraphs are as follows:

• Diagnostic tests must pass at 375 rpm of the speed data stored during the last failed test.
• Plus or minus ten percent of the engine load stored at the last failed test. Similar engine temperature conditions (heated or in the process of heating) with the conditions saved during the last unsuccessful check.

Compliance with these requirements ensures that the fault indicated by the malfunction indicator lamp is corrected.

The malfunction indicator lamp is located on the instrument panel and has the following functions:

• It informs the driver about a malfunction that affects the toxicity level and about the need to urgently deliver the car to a service station.
• When checking the system, the malfunction indicator lamp comes on when the ignition is on and the engine is not running. When the engine is started, the malfunction indicator lamp goes out.
• If the fault indicator light remains on while the engine is running, or there is a suspected problem with the vehicle's performance or toxicity issues, the onboard OBD diagnostic system must be checked. The procedures for these checks are given in the "OBD System Check". These checks can reveal problems that were not previously detected by other diagnostics.

Diagnostic connector

The means of exchanging data with the control module is the data link connector (DLC). The data link connector is used to connect a scan tool. Some examples of using a scan tool are given below:

• Identifying stored diagnostic trouble codes.
• Clear diagnostic codes.
• Conducting signal checks.
• Read serial data.

Types of diagnostic trouble codes

Each Diagnostic Trouble Code (DTC) is directly associated with a diagnostic check. The diagnostic management system sets diagnostic trouble codes based on failure to pass checks during a trip or trips. Specific checks require failure to complete two consecutive test trips, and only then will the diagnostic trouble code be set. Three types of diagnostic trouble codes are discussed below and their characteristics are described:

Type A

• Associated with the emission of harmful substances.
• The Malfunction Indicator Lamp (MIL) comes on immediately after a malfunction occurs.
• The controller records the operating conditions at the time a fault is detected. This information is stored in the status record buffer and fault logs.
• An archive of diagnostic trouble codes is saved.
• The malfunction indicator lamp turns off after three or four consecutive driving cycles in which the diagnostics did not detect a malfunction.
• The diagnostic trouble code history is cleared after 40 consecutive warm-up cycles without a fault.
• The diagnostic trouble code can be cleared using a scan tool.
• Disconnection of power to the ECM controller for 10 seconds.

Type E

• Associated with the emission of harmful substances.
• The malfunction indicator lamp comes on after 3 confirmed driving cycles.
• The controller records the operating conditions at the time a fault is detected. This information is stored in the status record buffer and fault logs.
• An archive of diagnostic trouble codes is saved.
• The malfunction indicator lamp turns off after three or four consecutive driving cycles in which the diagnostics did not detect a malfunction.
• The diagnostic trouble code history is cleared after 40 consecutive warm-up cycles without a fault.
• The diagnostic trouble code can be cleared using a scan tool.
• Disconnection of power to the ECM controller for 10 seconds.

Type C

• Not associated with the emission of harmful substances.
• As soon as an error occurs, the Service Vehicle Soon (SVS) indicator lights up.
• The ECM records operating conditions at the time faults are detected. This information is stored in the fault records.
• An archive of diagnostic trouble codes is saved.
• The SVS indicator lamp turns off after a trip in which diagnostics did not detect a malfunction.
• The diagnostic trouble code history is cleared after 20 consecutive warm-up cycles without faults.
• The diagnostic trouble code can be cleared using a scan tool.
• Power failure of the ECM controller for more than 10 seconds.

Important: Only four failure reports can be stored. Each failure report is for a separate diagnostic trouble code. If multiple diagnostic trouble codes are set, it is possible that there will not be a failure report for each code.

Reading diagnostic trouble codes

Reading diagnostic trouble codes is done with a diagnostic scan tool. When reading diagnostic trouble codes, follow the tool manufacturer's instructions.

Diagnostic Trouble Code Modes

On-Board Diagnostic (OBD) equipped passenger vehicles, there are five options for displaying expanded DTC information on the scan tool. The new modes, DTC information, and special DTCs are described below. Once a DTC is selected, the following menu appears:

• Diagnostic trouble code information.
• A specific diagnostic trouble code.
• Recording the state.
• Fault logs (not all programs).
• Clear information.

Below is a brief description of each submenu in DTC Information and Specific DTC. They are listed in alphabetical order but may appear differently on your scan tool.

Diagnostic Trouble Code Information Mode

Use the Diagnostic Trouble Code Information mode to search for a specific type of stored trouble code information. There are seven options to choose from. The service manual may instruct the technician to check for diagnostic trouble codes in a specific way. Always follow the specified service procedures.

To obtain a full description of any status, press the "Enter" key before pressing the desired function key. For example, pressing the "Enter" key rather than the function key will display a description of the scan tool status abbreviation in use.

Diagnostic Trouble Code Status

This selection will display DTCs that have not been run in the current ignition cycle or have reported a failed test in this cycle, the maximum number of DTCs that can be displayed is 33. Run and pass tests will clear this number from the scan tool display.

Fail This Ign. (Fail This Ignition - Failures This Ignition Cycle)

This selection displays the failed diagnostic trouble codes for this ignition cycle.

Archive

This selection displays only diagnostic trouble codes stored in the ECM controller's memory. It does not display diagnostic trouble codes that have not been accessed by the fault indicator light. It displays diagnostic trouble codes for all types A and E that have accessed the fault indicator light and failed during the last 40 heating cycles. In addition, Type C DTCs that occurred during the last 20 warm-up cycles are displayed.

Last Test Fail (Failed DTCs in last check)

This option displays the failed diagnostic trouble codes of the last check. The last check may have occurred in the previous ignition cycle if a diagnostic fault code of type A or E is displayed. For Type C diagnostic trouble codes, the last failed check must have been passed in the current ignition cycle to be displayed as Last Test Fail (Failed DTCs in last check).

MIL Request (Addressing the Malfunction Indicator Lamp)

This selection will only show DTCs that request the MIL. This selection will only report a Type A or E DTC after the MIL has been requested.

Not Run SCC (Not Run Since Code Clear - Not run since the last code clear)

This option displays up to 33 diagnostic trouble codes that have not been executed since the diagnostic trouble codes were last cleared. Since the displayed diagnostic trouble codes have not been executed, their status (successful or unsuccessful) unknown.

Test Fail SCC (Test Failed Since Code Clear - Test failed since last code clear)

This selection displays all active and archived diagnostic trouble codes that have reported a failed scan since the last time the diagnostic trouble codes were cleared. Diagnostic trouble codes that were unsuccessful for more than 40 heating cycles before selecting this option are not displayed.

Specific DTC Mode (Diagnostic Trouble Code Special Mode)

This mode is used to check the status of individual diagnostic tests by DTC number. This selection can be made if the DTC was successful, unsuccessful, or both. Many descriptions of the EOBD DTC mode are possible due to the large amount of information that the diagnostic executive monitors for each test. Below are some possible descriptions with a brief explanation.

In this mode, the "F2" key is used to display the DTC description. The "Yes" and "No" keys can be used to display more information about the DTC status. This selection only allows the entry of DTC numbers that are supported by the vehicle being tested. If you attempt to enter DTC numbers that the diagnostic executive program does not recognize, the requested information will not be displayed correctly and the scan tool may display an error message. The same applies to using the Snapshot Mode startup option. If an invalid DTC is entered, the scan tool will not start.

Failed Last Test (Last check failed)

This message reports the failure of the last test for the selected diagnostic trouble code. For type A and E diagnostic trouble codes, this message will be displayed during subsequent ignition cycles until the test is passed or the diagnostic trouble codes are cleared. For type C and D diagnostic trouble codes, this message will be cleared at the end of the last ignition cycle.

Failed Since Clear (Unsuccessful since clearing)

This message indicates that the DTC has failed at least once in the last 40 warm up cycles since the DTCs were cleared.

Failed This Ig. (Failed This Ignition - Failed to test this ignition)

This message indicates that the diagnostic fault code failed at least once during the current ignition cycle. This message is cleared when the diagnostic trouble codes are cleared or when the last ignition cycle is completed.

Archive

This message indicates that a diagnostic trouble code has been stored in memory as a current fault. A diagnostic trouble code displayed as a history fault does not mean that the fault is not present. The history description means that all conditions for reporting the fault have been met (perhaps even current ones), and that the information was stored in the control module memory.

MIL Requested (The malfunction indicator lamp is addressed)

This message indicates that the diagnostic fault code is currently causing the fault indicator light to turn on. Please note that only diagnostic trouble codes such as A and E can refer to the fault indicator light. Reference to the fault indicator light cannot be used to determine the current presence of a fault condition. This is because the executive diagnostic program requires up to three successful diagnostic trips to turn off the fault indicator light.

Not Run Since CI (Not Run Since Cleared - Not run since last cleared)

This message indicates that the selected DTC has failed since the DTCs were cleared. Therefore, the diagnostic status (successful or unsuccessful) unknown After clearing the diagnostic trouble codes, this message will display until the diagnostic test is performed.

Not Run This Ig. (Not Run This Ignition - Not run this ignition test)

This message indicates that the selected diagnostic trouble code has not been executed during the current ignition cycle.

Test Ran and Passed (The test has been completed and passed)

This message indicates that the selected diagnostic trouble code has done the following:

• Passed the final check.
• The test has been performed and passed during the current ignition cycle.
• The test has been performed and passed since the last time the DTCs were cleared.

If the vehicle status is displayed as "Test Ran and Passed" after checking the repair, this means that the car is ready to be delivered to the customer.

If the vehicle status is displayed as "Failed This Ignition" after checking the repair, it means that the repair is not finished and other checks are required.

Before repairing the vehicle, the status information can be used to evaluate the diagnostic test status and to help identify an intermittent problem. The technician may conclude that although the MIL is illuminated, the fault condition is due to the absence of the required code. The cause must be an intermittent condition.

Primary Systems Based Diagnostics

There are primary systems-based diagnostics that evaluate system performance and its impact on toxicity. The primary systems-based diagnostics are described below with a brief commentary on the diagnostic functions:

Oxygen sensor diagnostics

The oxygen control sensor (HO2S1) is diagnosed by the following conditions:

• Slow response.
• Response time (time to switch between R/L and L/R).
• Inactive signal (the output signal is flat at an offset voltage of about 450 mV).
• The signal is recorded high.
• The signal is fixed low.

The oxygen sensor (HO2S2) diagnostic is diagnosed by the following conditions:

• Heater operation (cold start activity time).
• Signal is low at constant speed or in power enrichment mode (rapid acceleration when mixture enrichment should be indicated).
• The signal is recorded high at constant speed or in braking mode (braking when lean mixture should be displayed).
• Inactive sensor (the output signal is flat at about 438 mV).

If the pigtail, connector or terminal is damaged, the entire oxygen sensor assembly must be replaced. Do not attempt to repair the wires, connector or terminals. The sensor must be referenced to clean air to ensure proper operation. This reference is provided by the oxygen sensor wires. Attempting to repair the wires, connector or terminals may restrict the flow of clean air and impair oxygen sensor performance.

Diagnostic operation to check for misfire

Misfire check diagnostics are based on changes in crankshaft speed (control period). The ECM detects the crankshaft speed using the crankshaft position (CKP) sensor and the camshaft position (CMP) sensor. When a cylinder misfires, the crankshaft slows down momentarily. By monitoring the CKP and CMP sensors, the ECM can calculate when the misfire occurred.

In the event of a misfire that is damaging the catalytic converter, a diagnostic that monitors the misfire between 1000 and 3200 engine speeds will be required.

In the case of a misfire that does not damage the catalytic converter, the diagnostics will respond to a misfire within 200 engine revolutions

A rough road can cause a misfire to be detected incorrectly. A rough road causes torque to be applied to the drive wheels and transmission drive. This torque can temporarily reduce the crankshaft speed. This can be detected incorrectly as a misfire.

The rough road sensor or G-sensor works in conjunction with the misfire detection system. The G-sensor produces a signal that changes with the intensity of road vibration. When the ECM detects a rough road, the misfire detection system is temporarily disabled.

Misfire counter

When a cylinder misfires, the misfire diagnostics counts the misfires and records the crankshaft position at the time of the misfire. These "misfire counters" are essentially recorders on each cylinder. Current and historical misfire counters are maintained for each cylinder. Current misfire counters (Misfire Cur #1-4) display the number of ignitions out of 200 cylinder ignitions that were missed. The current misfire meter displays real-time data without saving the misfire diagnostic trouble codes. Archived Ignition Misfire Counters (Misfire Hist #1-4) display the total number of misfires that occurred. The misfire history counters display 0 until the misfire diagnostic passes and DTC P0300 is set. Once DTC P0300 is set, the misfire history counters will be updated every 200 misfires. Misfire counters are maintained for each cylinder.

If the misfire diagnostics fails, the diagnostic executive will check all misfire counters before reporting a diagnostic trouble code. This way, the diagnostic executive reports the most current information.

If the crankshaft rotation is irregular, a misfire is detected. Due to this irregular condition, the data collected by diagnostics can sometimes incorrectly indicate which cylinder is misfiring.

Use diagnostic equipment to monitor misfire data on OBD-compliant vehicles. Knowing which cylinder is misfiring can help isolate the chain, even when dealing with multiple misfires. Using the misfire counter information, determine which cylinder is misfiring. If the counters are misfiring cylinders 1 and 4, find the common circuit or component for both cylinders 1 and 4.

Misfire diagnostics can identify a temporary fault that is not necessarily related to a faulty emission control system. Possible causes include:

• Contaminated fuel.
• Low fuel level.
• Flooded spark plugs.
• General engine failure.

Diagnostic operation to check fuel trim

This system tracks the average values of short-and long-term fuel supply adjustments. If these fuel supply adjustment values stop at the limit values for the specified time, a fault is displayed. Fuel supply adjustment diagnostics compares the average values of short-term and long-term fuel supply adjustments with the threshold values of the enriched and depleted fuel mixture. If at least one of the values is within the threshold, the normal state is recorded. If both values exceed the limit values, a diagnostic fault code for enrichment or depletion of the mixture is recorded.

Fuel supply adjustment diagnostics also performs checks with changing operating modes. The test determines whether the enriched state is caused by excessive gasoline vapors in the SUPB adsorber. In order to comply with the OBD requirements, the control module uses weighted fuel correction cells to determine whether the fuel supply adjustment diagnostic fault code needs to be set. The fuel supply adjustment diagnostic fault code is set only if the values of the fuel supply adjustment counters in the weighted correction cells exceed the technical specifications. This means that the car may have a problem adjusting the fuel supply, which under certain conditions causes other problems (eg high idle speed due to small vacuum leak or rough idle due to large vacuum leak), and the vehicle operates normally at other times. No fuel trim diagnostic trouble code will be set (although an idle speed or HO2S2 sensor DTC may be set). Use a scan tool to monitor the fuel trim meters when the problem occurs.

The Fuel Trim DTC can be caused by several vehicle faults. Use all available information (other stored diagnostic trouble codes, lean or rich) when diagnosing a fuel injection adjustment malfunction.

Diagnostic weights of fuel trim cells

The fuel supply adjustment diagnostic fault code will not be set, regardless of the fuel supply adjustment counter in cell 0, unless the counter in the weighted cells is outside the technical specifications. This means that the car may have a problem adjusting the fuel supply, which under certain conditions causes other problems (eg high idle speed due to small vacuum leak or rough idle due to large vacuum leak), and the vehicle operates normally at other times. No fuel trim diagnostic trouble code will be set (although an idle speed or HO2S2 sensor DTC may be set). Use a scan tool to monitor the fuel trim meters when the problem occurs.