Troubleshooting automatic transmission
Note:
- Automatic transmission malfunctions can be caused by improper maintenance, improper adjustment or malfunction of the electronic control system of the automatic transmission, mechanical malfunction of the transmission, malfunction of the automatic transmission hydraulic control system, insufficient engine power, or a combination of these malfunctions. Therefore, before starting the test, it is necessary to determine the area of \u200b\u200bthe malfunction (engine, control system or gearbox).
- Troubleshooting should start with the simplest operations and continue in order of increasing complexity.
1. Check for signs of automatic transmission malfunctions and the conditions under which they occur.
2. Read diagnostic trouble codes. Write down the trouble codes, and then clear the codes from the memory of the automatic transmission electronic control unit.
3. Perform basic checks and adjustments (checking tire pressure, checking the level and condition of the automatic transmission fluid, checking the automatic transmission control mechanism, etc.), for which the deviation from the norm can be easily determined.
Note: analysis of the results of checking the automatic transmission fluid level:
- If the automatic transmission fluid level is lower than required, then the automatic transmission pump will capture the fluid along with air, which will lead to various malfunctions. Air bubbles entering the automatic transmission hydraulic system cause oil foaming. This will cause unstable pressure in the hydraulic system, which in turn will lead to a delay when shifting gears (late gear shifting) and slipping clutches or brakes, etc.
- If the level of the automatic transmission fluid is higher than required, then due to the rotation of the gears of the planetary mechanisms, abundant foaming will occur, which will lead to the same consequences as in the case of a low level of the automatic transmission fluid, and will cause premature deterioration of the working fluid.
- In both cases, air bubbles cause overheating, oxidation of the working fluid and varnish deposits that damage valves, couplings and actuators. Foaming also causes fluid to escape through the transmission breather, which is mistaken for leaks.
4. Carry out a road test to determine the need for further automatic transmission diagnostics.
- A) Check for proper gear shifting. Check the electrical part of the control system if the gear shift is correct.
- b) Make sure the problem is only with the automatic transmission. If there is noise or vibration, the compressor, engine, etc. are possible sources.
5. Read diagnostic trouble codes (re).
- A) If fault codes are displayed when there is a symptom of a malfunction, then refer to subsection "Reading Diagnostic Trouble Codes".
- b) If there is a symptom (no fault codes) or in the absence of a symptom of a malfunction, it is necessary to check for the presence of fault codes read before road testing. If fault codes are displayed, then refer to subsection "Reading Diagnostic Trouble Codes", if fault codes are not displayed, then refer to subsection "Troubleshooting by their symptoms" section "Troubleshooting automatic transmission".
6. If a possible cause is a malfunction in the automatic transmission electronic control system. then use a tester or oscilloscope to check the input and output signals of the automatic transmission electronic control unit.
- A) If there are incorrect input and output signals of the automatic transmission control unit, then check the wiring according to the appropriate wiring diagram.
- b) If no fault is found when checking the wiring, then check the individual components of the system.
7. If the signals of the electronic control system are normal or if a possible cause is a malfunction in the automatic transmission control hydraulic system, then check the pressure in the automatic transmission control hydraulic system (hydraulic test). If the condition of the hydraulic system differs from the required, then perform the appropriate checks and adjustments in section "Checking the mechanical systems of automatic transmission".
8. If the pressure in the automatic transmission control hydraulic system is correct or if a malfunction in the main automatic transmission system is a possible cause (mechanical part), then check the engine and torque converter with the vehicle fully braked (stall-test), identify the defective part and make the necessary overhaul.
9. After completing the repair, perform a road test to verify that the problem has been corrected.
Reading Diagnostic Trouble Codes
1. Prepare the vehicle for inspection.
- A) Make sure the battery is in good condition, as fault detection is not possible when the battery voltage is low.
- b) Turn off all additional equipment.
- V) Set the automatic transmission selector to position "N".
Attention: do not disconnect the battery until the diagnostic results are completely read, as the fault code will be deleted from the memory of the electronic control unit when the battery or the engine control unit connector is disconnected.
3. Connect a tester to a diagnostic socket.
Attention: before connecting the tester, turn off the ignition.
4. Turn on the ignition and read the diagnostic codes.
5. Determine the malfunction by the diagnostic code (see table "Codes of malfunctions of the automatic transmission control system").
6. After reading the diagnostic codes, turn off the ignition and disconnect the tester.
Explanations on the operation of the self-diagnosis system
1. Fault codes.
- A) A description of the structure of the standard diagnostic trouble code is given in the chapter "fuel injection system".
- b) A maximum of 8 diagnostic trouble codes can be written to the RAM of the electronic control unit (in the order they appear).
- V) If a fault code appears repeatedly, it will be stored in memory only once.
- G) If the number of recorded DTCs or fault conditions exceeds 8, the previously recorded fault codes will be replaced in memory with new codes in sequence, starting from the earliest.
Caution: Do not disconnect the battery before reading diagnostic trouble codes or fault conditions, as if the battery is disconnected, they will be cleared from the memory of the electronic control unit.
Note:
- If DTC P0715 occurs 4 times, then the transmission goes into emergency mode (gear shift blocked) and locks in 3rd gear or 2nd gear.
- If DTC P0720 occurs 4 times, then the transmission goes into emergency mode (gear shift blocked) and is fixed in 3rd gear or 2nd gear, automatic transmission range indicator "N" flashes at a frequency of 1 Hz.
- If one of the indicated fault codes occurs 4 times, then the transmission goes into emergency operation (gear shift blocked) and is fixed in 3rd gear: P0731, P0732, P0733, P0734, P0736.
- If one of the indicated fault codes is stored in the memory of the electronic control unit, then the gearbox goes into emergency operation (gear shift blocked) and is fixed in 3rd gear: P0740, P0743, P0750, P0755, P0760, P0765, P1723.
2. Emergency operation codes.
- A) If the system has switched to emergency control mode and the gearbox is fixed in 3rd gear (gear shift blocked), then a diagnostic trouble code is written to the RAM of the electronic control unit in the form of an emergency operation code.
- b) A maximum of 3 emergency operation codes can be stored in memory. If the number of recorded codes (emergency mode parameters) exceeds 3, the previously recorded codes will be replaced in memory with new codes in sequence, starting from the earliest. The same fault code cannot be stored in memory more than once.
- V) If the gearbox only works in third gear (gear shift blocked) and the ignition key is turned to position "OFF" (OFF), then the emergency operation will be canceled, but the diagnostic trouble codes will be stored in the RAM of the electronic control unit.
3. Automatic removal of fault codes from memory.
All diagnostic trouble codes are automatically deleted from the memory after the temperature of the working fluid in the automatic transmission reaches 50°C 200 times after the last trouble code is written to the memory.
4. Forced deletion of fault codes from memory.
Stored diagnostic trouble codes can be cleared using a tester if the following conditions are met:
- The ignition key is in the position "ON".
- No signals were detected from the crankshaft position sensor, transmission speed sensor, and vehicle speed sensor.
- The emergency mode of the automatic transmission is not activated.
Instructions for troubleshooting by their symptoms
1. Automatic transmission malfunctions can be caused by a malfunction of the engine systems, improper adjustment or internal malfunction of the electronic or hydraulic control systems of the transmission, mechanical failure of the transmission. Therefore, always start the diagnosis by checking the level and condition of the working fluid in the automatic transmission and adjusting the control cables.
2. Checking engine systems means checking the engine management system, ignition system, fuel system, as well as the engine itself.
3. Checking the parts of the gearbox housing means checking the clutches, brakes, and internal gears of the gearbox.
4. When checking the control valve block, pay attention to the tightening torques of the bolts, damage or displacement of the sealing rings, valves and their bushings from their places. If damage cannot be repaired, replace the control valve block assembly.
5. Check the torque converter for proper installation (lack of distortion, etc.) and spline damage. If the splines are damaged and repair is not possible, replace the torque converter.