- Make sure the customer's complaint is validated. To ensure that the customer's complaint is validated, the foreman must be familiar with the normal operation of the system.
- Carry out preliminary checks as follows:
- Carry out a thorough visual check.
- View archive of completed repairs.
- Identify unusual sounds or smells.
- Gather information about diagnostic trouble codes to ensure efficient repair.
- Check bulletins and other service information. This includes videos, newsletters, etc.
- View service information (instructions) for checking the system.
- See service diagnostics.
No faults found
This condition occurs when the vehicle is deemed to be operating normally. The condition described by the customer may be normal. Make sure that the customer's complaint is confirmed on the basis of another normally working car. The state may be unstable. Check the complaint under the conditions described by the customer before releasing the vehicle.
Recheck the complaint.
If the complaint cannot be successfully found or located, a reassessment is necessary. The complaint must be re-examined and may be intermittent, as defined in section "Intermittent faults" or may be a normal condition.
After localizing the cause, repairs should be carried out. Verify normal operation and that the symptom has been corrected. This may include sea trials or other methods necessary to confirm that the problem has been corrected under the following conditions:
- Terms specified by the client.
- If a DTC was diagnosed, test for repairs under the same conditions in which the DTC was set, as recorded in the fault logs and status record data.
Check car repair.
The vehicle repair check will be more complete on vehicles with a diagnostic system. When performing repairs, the master must perform the following steps:
Important: Follow the steps below when checking OBD repair (OBD). Failure to follow these steps may result in unnecessary repairs.
- View and record fault logs and status record data for diagnosed fault codes (status record data is only stored for type A or E diagnostics and only if a MIL has been requested).
- Clear diagnostic trouble codes.
- Drive under the conditions recorded in the fault log and these condition records.
- Check the DTC status information for the DTC that was diagnosed when running the diagnostic test for that DTC.
Ease of maintenance of the on-board diagnostic system
Based on the experience of the on-board diagnostic system (OBD) 1994 and 1995 vehicles, a list of non-automotive faults has been compiled that may affect the performance of the OBD system. These non-automotive faults depend on the environmental conditions and the quality of the fuel used. With the introduction of OBD diagnostics for the passenger car and light truck market in 1996, a malfunction indicator lamp illuminating from non-automotive faults can lead to vehicle misdiagnosis, higher warranty costs and customer dissatisfaction. The following list of non-automotive faults does not include all possible faults and does not apply equally to all model lines.
Fuel quality
Fuel quality is not a new topic in the automotive industry, but its impact on MIL activation with OBD systems is new.
Fuel additives such as "dry gas" or "octane correctors" may affect the characteristics of the fuel. If this results in incomplete or partial combustion, DTC P0300 will set. Saturated vapor pressure can create problems in the fuel system, especially during the autumn and spring seasons when ambient temperatures fluctuate greatly. High vapor pressure may look like a fuel trim DTC due to excessive load on the carbon filter. High vapor pressure in the fuel tank can also affect the diagnosis of fuel vapor emission.
Using fuel with the wrong octane rating can cause drivability problems. Many major fuel companies advertise gasoline grades "Premium" as a way to improve the performance of your vehicle. In most brands "Premium" alcohol is used to increase the octane number. Although alcohol additives increase the octane number, the ability to evaporate at cold temperatures deteriorates. This reduces the starting properties and performance of a cold engine.
Low fuel levels can lead to fuel starvation, lean mixture and possibly misfiring.
Non-original knots
All OBD diagnostics have been tuned to work with original (OEM) nodes. A common situation is that a powerful exhaust system, acting on back pressure, can affect the operation of the EGR valve and thus turn on the malfunction indicator lamp. Small leaks in the exhaust system near the catalytic converter oxygen sensor can also cause the MIL to come on.
Additional electronic equipment such as cellular phones, stereos, anti-theft systems can cause electromagnetic interference if not properly installed. This can cause false sensor readings and turn on the MIL.
Environment
Temporary environmental conditions, such as local flooding, affect the operation of the vehicle's ignition system. If the ignition system is exposed to rain, it may cause misfiring and turn on the MIL.
Car delivery
Transportation of new vehicles from assembly to dealers involves at least 60 ignition cycles over 2 to 3 mile trips. This type of driving contributes to fouled spark plugs and causes the MIL to illuminate and DTC P0300 to set.
Poor maintenance
The sensitivity of the OBD diagnostic system will cause the MIL to come on if the vehicle has been improperly repaired. Clogged air and fuel filters, deposits in the crankcase due to poor oil circulation or improper oil viscosity can lead to malfunctions that were not detected prior to OBD. Poor maintenance cannot be classified as "non-automotive malfunction", but due to the high sensitivity of OBD diagnostics, the maintenance schedule must be followed as accurately as possible.
Strong vibration
The misfire diagnostic measures small changes in engine speed. Severe driveshaft vibration caused by excessive wheel contamination can have the same effect on crankshaft speed as a misfire and may therefore set DTC P0300.
Adverse system failures
Many OBD diagnostic systems may not work if the ECM detects a malfunction in a dependent system or component. For example, if the ECM detects a misfire, the catalytic converter diagnostic will be suspended until the misfire fault is corrected. If the misfire fault is significant enough, the catalytic converter may be damaged by overheating and will not set a catalyst DTC until the misfire fault is corrected and the converter diagnostic is completed. In this case, the client will have to come to the service station twice to repair the car.
Serial data interface
Serial data interface GMLAN
General Motors LAN (GMLAN) car - a family of serial communication buses (subnets), which allow electronic control devices (ECU or nodes) communicate with each other or with the diagnostic tester.
GMLAN supports three buses, a high-speed two-wire bus, a medium-speed two-wire bus, and a single-wire low-speed bus.
- high speed bus (500 kbps) - typically used to share real-time data such as driver-specified torque, actual engine torque, steering angle, etc.
- Medium speed tire (approximately 95.2 kbps) - usually used for informational support (display, navigation, etc.), where the response time of the system requires that a large amount of data be transmitted in a relatively short time, such as updating the display of graphical information.
- low speed bus (33.33 kbps) - typically used for driver-controlled devices where system response time requirements are in the order of 100-200 ms. This bus also supports high speed operation at 83.33 kbps, used only when reprogramming the ECU.
The decision to use a particular tire on a given vehicle depends on what functions are shared among the various ECUs on that vehicle.
GMLAN buses use controller network communication protocol (CAN). The data is packed into CAN·messages, which are segmented into "frames" CAN. Each CAN frame includes header data (also known as the CAN identifier, or CANId) and a maximum of eight (8) bytes of data. A message may consist of a single frame or multiple frames, depending on the number of data bytes that define the complete message. Link arbitration occurs only on the header, or CANId, part of the frame.
On-Board Diagnostic Checks (OBD)
A diagnostic is a sequence of steps that results in a report to the agent about the success or failure of the diagnostic. If the diagnostic test passes, the diagnostic executor captures the following data:
- The diagnostic check after the last ignition cycle is completed.
- The diagnostic test passed during the current ignition cycle.
- The fault identified by the diagnostic check is not currently active.
If the diagnostic check fails, the diagnostic executor logs the following data:
- The diagnostic check after the last ignition cycle is completed.
- The fault identified by the diagnostic check is now active.
- The fault was active during this ignition cycle.
- Operating parameters at the time of the occurrence of the fault.
Be aware that a fuel trim DTC can be caused by a list of automotive faults. Use all available information (other stored DTCs, lean or rich mixture) when diagnosing a fuel trim fault.
General diagnostics of vehicle systems
General diagnostics of vehicle systems is required to monitor the input and output signals of transmission components related to emission control.
Input Components
Input components are monitored for continuity and out of range signals. This includes validation. Validity check determines the correctness of the signal received from the sensor, i.e. Throttle position sensor indicating high throttle position at low engine load or low manifold absolute pressure sensor signal. Input components may include but are not limited to the following sensors:
- Vehicle speed sensor (VSS)
- crankshaft position sensor (CKP)
- Throttle position sensor (TP)
- coolant temperature sensor (ECT).
- Camshaft position sensor (SMR).
- Manifold absolute pressure sensor (IDA).
In addition to circuit integrity and plausibility checks, the coolant temperature sensor is monitored for its ability to achieve a constant temperature for fuel monitoring in a closed loop.
Output Components
Output components are checked for correct responses to control module commands. Components that cannot be functionally tested are monitored for continuity and out-of-range signals. Output components may include but are not limited to the following sensors:
- Idle control motor.
- EVAP adsorber purge solenoid valve, controlled by the control module.
- Air conditioning relay.
- Cooling fan.
- VSS output.
- Malfunction indicator lamp control.
See «ECM controller» and sensors in this section.
Passive and active diagnostic checks
The Passive Diagnostic Test simply tests the vehicle's systems and components. In contrast, an active test takes some action in the performance of diagnostic functions, often in response to a failed passive test. For example, an active EGR diagnostic test causes the EGR valve to open on closed throttle braking and/or close at steady speed. Any of these actions should result in a change in manifold pressure.
Diagnostic checks with changing modes of operation
These are any on-board diagnostic control system checks that may affect vehicle performance or emission levels.
Heating cycle
The heat cycle means that the engine temperature must reach a minimum of 160°F (70°С) and descend at least 72°F (22°С) for the trip.
Status Record
Status Record (Freeze Frame) is an element of the diagnostic control system that stores various vehicle information at the time an emission control fault is stored in memory and the MIL is turned on. This data can help determine the cause of the malfunction.
Fault log
Fault log is an advanced OBD status recording function. The fault log stores the same information as the status record, but it stores any fault information in the on-board memory, while the fault log only stores information about emissions related faults activating the MIL.