Diagnostics
Word "diagnostics" refers to any on-board test conducted by the vehicle's diagnostic control system. Diagnostics is simply a test run of a system or components to determine if they are operating within specifications. There are several diagnostics presented in the following list:
- Misfire
- Control oxygen sensor (HO2S1)
- Diagnostic oxygen sensor (HO2S2)
- Exhaust Gas Recirculation (EGR)
- Neutralizer efficiency control
Activation Criteria
Term "activation criteria" is a technical term for the conditions required to run a given diagnostic test. Each diagnostic has a special list of conditions under which the diagnostic is triggered.
"Activation Criteria" is, in other words, "required conditions".
The activation criteria for each diagnostic are listed on the first page of the DTC description under the heading "Conditions for Setting the DTC". The activation criteria for different diagnostics differ from each other and, as a rule, include the following:
- Engine speed
- Vehicle speed
- Coolant temperature (ECT)
- Manifold absolute pressure (IDA)
- barometric pressure (BARO)
- Intake air temperature (IAT)
- Throttle position (TP)
- Strong charcoal filter purge
- Fuel trim
- A/C on
Drive
Technically, a trip is an ignition on and off cycle in which the criteria for activating this diagnostic are met, allowing it to be carried out. Unfortunately, this concept is not so simple. A trip is considered valid when all the activation criteria for a given diagnostic are met. But since the activation criteria change from one diagnostic to another, the definition of a trip changes too. Some diagnostics only work at engine operating temperature, some only work after the engine is started, some require a constant line speed, others only work at idle or with the torque converter clutch disengaged. Some only work immediately after a cold start.
Thus, a diagnosis is defined as an ignition on and off cycle in which the vehicle has operated in a manner that satisfies the criteria for that diagnosis, and the diagnosis recognizes such a cycle as a single trip. However, another diagnostic with a different set of activation criteria (which have not been met) during the trip will not be considered a trip. A trip specific diagnostic will not take place if the vehicle is not operating in accordance with all activation criteria.
Diagnostic Information
Diagnostic tables and functional checks are designed to find the faulty circuit or component in a logical decision process. The tables have been prepared on the assumption that the vehicle was in good working order at the time of assembly and that there were no malfunctions.
Continuous diagnostics of certain control functions is provided. The diagnostic capabilities are supplemented by the diagnostic procedures contained in this manual. The language of communication about the source of the malfunction is the system of diagnostic trouble codes. When a malfunction is detected by the control module, a DTC is set and the MIL is illuminated.
Malfunction indicator lamp
The Malfunction Indicator Lamp (MIL) illuminates when the set of conditions required by the OBD system is strictly met (OBD).
Typically, the Malfunction Indicator Lamp (MIL) will illuminate when the ECM detects a DTC that has a significant effect on vehicle emissions.
The MIL is controlled by the diagnostic executive. The Malfunction Indicator Lamp (MIL) illuminates if the Diagnostic Emission Test determines a malfunction. It remains illuminated until the system or component has passed the same test for three trips without any faults in the emission control system.
Turning off the malfunction indicator lamp
When the Malfunction Indicator Lamp (MIL) is illuminated, the diagnostic executive turns it off after three consecutive trips with a result of "verification passed" on the diagnosis that caused the MIL to come on. Although the MIL turns off, a DTC is stored in the ECM memory (both in the status record and in the fault log) until the end of forty (40) heating cycles without faults.
If the MIL was turned on by a fuel trim or an emission control DTC, additional requirements must be met. Additional requirements to those described in the previous paragraphs are:
- The diagnostic tests must pass at 375 RPM of the RPM data stored from 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 from the last failed check.
Compliance with these requirements ensures that the malfunction 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 level of toxicity, and about the need to urgently transport the car to a service station.
- When checking the system, the Malfunction Indicator Lamp (MIL) comes on when the ignition is on and the engine is not running. When the engine is started, the MIL will turn off.
- If the Malfunction Indicator Lamp (MIL) stays on while the engine is running, or vehicle performance or toxicity problems are suspected, an OBD system diagnostic test should be performed. The procedures for these checks are given in "OBD system check". These checks can reveal faults not previously detected by other diagnostics.
Diagnostic block
The means of data exchange with the control module is the diagnostic block (DLC). The diagnostic terminal is used to connect the scan tool. Some examples of using the scan tool are given below:
- Identification of stored DTCs.
- Clearing diagnostic codes.
- Conducting signal checks.
- Reading serial data.
Types of Diagnostic Trouble Codes
Each diagnostic trouble code (DTC) directly related to the diagnostic test. The Diagnostic Management System sets DTCs based on test failures during a trip or trips. Specific checks require two consecutive test runs not to be completed before the DTC is set. The following are three types of DTCs and the characteristics of these codes:
Type A
- Associated with the release of harmful substances.
- Malfunction indicator indicator lamp (MIL) lights up 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 stored.
- The Malfunction Indicator Lamp (MIL) will turn off after three or four consecutive driving cycles in which no fault is detected by the diagnostics.
- The DTC history is cleared after 40 consecutive heating cycles without faults.
- The DTC can be cleared with a scan tool.
- Power off the ECM for 10 seconds.
Type E
- Associated with the release of harmful substances.
- The MIL will come 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 stored.
- The Malfunction Indicator Lamp (MIL) will turn off after three or four consecutive driving cycles in which no fault is detected by the diagnostics.
- The DTC history is cleared after 40 consecutive heating cycles without faults.
- The DTC can be cleared with a scan tool.
- Power off the ECM for 10 seconds.
Type C
- Not associated with the emission of harmful substances.
- As soon as an error occurs, the indicator lights up "Perform vehicle maintenance as soon as possible" (SVS).
- The ECM records operating conditions at the time a fault is detected. This information is stored in fault logs.
- An archive of diagnostic trouble codes is stored.
- The SVS warning lamp turns off after a trip in which the diagnostics did not detect a malfunction.
- The DTC history is cleared after 20 consecutive heating cycles without faults.
- The DTC can be cleared with a scan tool.
- Power off the ECM for more than 10 seconds.
Important: Only four error reports can be saved. Each fail protocol is for a separate DTC. When multiple DTCs are set, it is possible that there will be no test failure protocol for each code.
Reading Diagnostic Trouble Codes
DTCs are read with a diagnostic scan tool. When reading diagnostic trouble codes, follow the instrument manufacturer's instructions.
Diagnostic Trouble Code Modes
On cars with on-board diagnostics (OBD) There are five options for displaying extended DTC information on the scan tool. A description of the new modes, DTC information and special DTCs is given below. After selecting a DTC, the following menu appears:
- Diagnostic trouble code information.
- Special diagnostic trouble code.
- State record.
- Fault logs (not all programs).
- Clear information.
Below is a brief description of each sub-menu in DTC Information and Special DTC. They are listed in alphabetical order, but may appear differently on the scan tool.
DTC Information Mode
Use the DTC Information Mode to search for a specific type of stored DTC information. There is a choice of seven options. The Service Manual may instruct the technician to check for DTCs in a certain way. Always follow the specified maintenance procedures.
For a complete description of any state, press the key "Enter" before pressing the desired function key. For example, pressing a key "Enter", rather than a function key, will display a description of the Scan Tool status abbreviation used.
Status of the diagnostic trouble code
This selection will display DTCs that did not run in the current ignition cycle or reported a failed test in this cycle, the maximum number of DTCs displayed is 33. Runs and successful tests result in that number being removed from the scan tool screen.
Fail This Ign. (Fail This Ignition - Failures of this ignition cycle)
This selection displays failed DTCs for this ignition cycle.
Archive
This selection only displays DTCs stored in the ECM memory. It does not display DTCs that did not refer to the Malfunction Indicator Lamp. It displays all Type A and E DTCs that have accessed the MIL and failed during the last 40 heat cycles. In addition, Type C DTCs that have occurred within the last 20 warm-up cycles are displayed.
Last Test Fail (Unsuccessful DTCs in last test)
This selection displays failed DTCs from the last test. The last test may have occurred in the previous ignition cycle if a Type A or E DTC is displayed. For Type C DTCs, the last failed test must have occurred in the current ignition cycle to be displayed as Last Test Fail (Unsuccessful DTCs in last test).
MIL Request (Accessing the Malfunction Indicator Lamp)
This selection will only show DTCs that request the MIL. This selection reports Type A or E DTCs only after the MIL has been requested.
Not Run SCC (Not Run Since Code Clear - Not executed since the last code clear)
This option displays up to 33 DTCs that have not been run since the last time the DTCs were cleared. Because the displayed DTCs have not been run, their status (successful or unsuccessful) unknown.
Test Fail SCC (Test Failed Since Code Clear - The test has failed since the last code clear)
This selection displays all active and historical DTCs that have reported test failures since the last time the DTCs were cleared. DTCs that have failed more than 40 heat cycles prior to selecting this option are not displayed.
Specific DTC Mode (Special mode of diagnostic trouble code)
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 agent monitors for each test. Below are some possible descriptions with a brief explanation.
In this mode, the key "F2" used to display a description of the DTC. Keys "Yes" And "No" can be used to display advanced DTC status information. This selection only allows the entry of DTC Info numbers that are supported by the vehicle being tested. If you attempt to enter DTC information numbers that the diagnostic executor does not recognize, the requested information will not display correctly and the scan tool may generate an error message. The same goes for using the launch option in snapshot mode. If an invalid DTC is entered, the scan tool will not start.
Failed Last Test (Last check failed)
This message provides information about the failed last test for the selected DTC. For Type A and E DTCs, this message will be displayed during subsequent ignition cycles until the test is passed or the DTCs are cleared. For Type C and D DTCs, this message will clear at the end of the last ignition cycle.
Failed Since Clear (Unsuccessful since cleaning)
This message indicates that the DTC has failed at least once in the last 40 heat cycles since the DTCs were cleared.
Failed This Ig. (Failed This Ignition - Unsuccessful test of this ignition)
This message indicates that the DTC failed at least once during the current ignition cycle. This message clears when the DTCs are cleared or when the last ignition cycle is completed.
Archive
This message indicates that a DTC has been stored in memory as a current fault. A DTC displayed as a historical fault does not mean that the fault is not present. Archived description means that all conditions for a fault message are met (maybe even current), and that the information has been stored in the control module's memory.
MIL Requested (The Malfunction Indicator Lamp is accessed)
This message indicates that a DTC is currently causing the MIL to illuminate. Note that only Type A and E DTCs can access the MIL. Referring to the Malfunction Indicator Lamp cannot be used to determine the current presence of a malfunction condition. This is because the diagnostic executive requires up to three trips with successful diagnostics to turn off the MIL.
Not Run Since CI (Not Run Since Cleared - Not done since the last cleanup)
This message indicates that the selected DTC has been unsuccessful since the DTCs were cleared. Therefore, the diagnostic status (successful or unsuccessful) unknown. After DTCs are cleared, this message will be displayed until a diagnostic check is performed.
Not Run This Ig. (Not Run This Ignition - Unchecked check of this ignition)
This message indicates that the selected DTC was not run during the current ignition cycle.
Test Ran and Passed (Test completed and passed)
This message indicates that the selected DTC did the following:
- Passed the last check.
- Test completed and passed during the current ignition cycle.
- Test completed and passed since DTCs were last cleared.
If the vehicle status is displayed as "Test Ran and Passed" after checking the repair, this means that the car is ready for delivery to the client.
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 the vehicle is repaired, the status information can be used to assess the status of the diagnostic test and as an aid to identifying an intermittent problem. The technician may conclude that although the MIL is on, the fault condition is caused by the missing code. The cause must be an unstable condition.
Diagnostics based on primary systems
There is a primary system-based diagnostic that evaluates system performance and its impact on toxicity. Primary system-based diagnostics are described below with a brief commentary on the diagnostic functions:
Oxygen Sensor Diagnosis
Control oxygen sensor (HO2S1) diagnosed under the following conditions:
- Slow response.
- Response time (time to switch between R/L and L/R).
- Inactive signal (the output signal is flat at a bias voltage of approx. 450 mV).
- The signal is fixed high.
- The signal is fixed low.
Diagnostic oxygen sensor (HO2S2) diagnosed under the following conditions:
- Heater operation (cold start active time).
- Signal stuck low at constant rpm or running in power enrichment mode (fast acceleration when rich mixture should be displayed).
- The signal is fixed high at constant speed or in braking mode (braking when lean should be displayed).
- Inactive sensor (output signal is flat at approx. 438 mV).
If the pigtail, connector, or terminal is damaged, the entire oxygen sensor group must be replaced. Do not attempt to repair wires, connector or terminals. To ensure normal operation of the sensor, it must be set to a reference point for clean air. This landmark is set by the wires of the oxygen sensor. Attempting to repair the wires, connector, or terminals may obstruct the passage of clean air and degrade the performance of the oxygen sensor.
Misfire Test Diagnostic Operation
Misfire check diagnostics based on changes in crankshaft speed (control period). The ECM determines the crankshaft speed using the crankshaft position sensor (CKP) and camshaft position sensor (SMR). When a misfire occurs in a cylinder, the crankshaft slows down instantly. By monitoring the crankshaft and camshaft position sensors, the ECM can calculate when a misfire occurs.
In the event of a misfire damaging the catalytic converter, diagnostics will be required to monitor the misfire between 1000-3200 engine rpm.
In the event of a misfire that does not damage the catalytic converter, diagnostics will respond to a misfire within 200 engine rpm
A rough road can lead to an erroneous misfire detection. The rough road causes torque to be applied to the drive wheels and transmission drive. This torque can temporarily reduce the crankshaft speed. This may be erroneously identified as a misfire.
The rough road sensor or G sensor works in conjunction with the misfire detection system. Sensor G produces a signal that changes with the intensity of the road vibration. When the ECM detects a rough road, the misfire detection system is temporarily disabled.
Misfire counter
When a cylinder misfires, the misfire diagnostic counts the misfires and records the position of the crankshaft at the time of the misfire. These "misfire counters" are essentially registrars 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 misfiring. The current misfire counter displays real-time data without storing misfire DTCs. Archived misfire counters (Misfire Hist #1–4) display the total number of ignitions that were misfiring. Historical misfire counters display 0 until the misfire diagnostic passes and DTC P0300 is set. After DTC P0300 sets, the history misfire counters will be updated every 200 ignitions. Misfire counters are maintained for each cylinder.
If the misfire diagnostic reports a malfunction, the diagnostic agent will check all misfire counters before reporting the DTC. Thus, the diagnostic executor provides the most up-to-date information.
If the rotation of the crankshaft is faulty, then a misfire is detected. Due to this fault condition, the data collected by the diagnostics can sometimes incorrectly indicate which cylinder is misfiring.
Use diagnostic equipment to monitor misfire data on OBD-compliant vehicles. Knowing which cylinder (Oh) misfire, it is possible to locate the circuit even when dealing with multiple misfires. Using the information from the misfire counters, determine which cylinder is misfiring. If the meters detect misfires in cylinders 1 and 4, find a common circuit or component for both cylinders 1 and 4.
The misfire diagnostic can identify a temporary problem that is not necessarily related to a problem with the emission control system. Possible reasons:
- Contaminated fuel.
- Low fuel level.
- Filled spark plugs.
- General engine failure.
Fuel Trim Check Diagnostic
This system monitors the average of short term and long term fuel trims. If these fuel trim values stop at the limits for a given time, then a fault is displayed. The fuel trim diagnostic compares the average short-term and long-term fuel trim values to the rich and lean thresholds. If at least one of the values is within the threshold, the normal state is fixed. If both values are outside the limits, a rich or lean DTC is set.
The fuel trim diagnostic also performs variable mode checks. The check determines if the rich condition is caused by excessive gasoline vapors in the EVAP canister. To comply with OBD requirements, the control module uses weighted trim fuel cells to determine if a fuel trim DTC should be set. The fuel trim DTC will only set if the fuel trim counters in the weighted trim cells are out of specification. This means that the vehicle may have a fuel trim problem that causes other problems under certain conditions (e.g. high idle due to small vacuum leak or rough idle due to large vacuum leak), and at other times the car works normally. Fuel Trim DTC will not set (although idle speed or HO2S2 oxygen sensor DTCs may be set). Use a scan tool to monitor the fuel trim meters at the time of the problem.
A fuel trim DTC can be caused by several vehicle problems. Use all available information (other stored DTCs, lean or rich mixture) when diagnosing a fuel trim fault.
Fuel Trim Cell Diagnostic Weights
The fuel trim DTC will not set, regardless of the fuel trim counter in location 0, unless the counter in the weighted cells is out of specification. This means that the vehicle may have a fuel trim problem that causes other problems under certain conditions (e.g. high idle due to small vacuum leak or rough idle due to large vacuum leak), and at other times the car works normally. Fuel Trim DTC will not set (although idle speed or HO2S2 oxygen sensor DTCs may be set). Use a scan tool to monitor the fuel trim meters at the time of the problem.