CLASS2 communications network maintenance should note the following points: 1, CLASS2 allowed to pass data between each other as the control unit also allows communication with the control unit fault diagnostic these. The control unit is a body control unit BCM (BCM D-CAR cars not access CLASS2), electronic brake control unit, control unit air conditioning systems, air bag control unit, a combination of instruments, power system control unit and key confirmation PCM system control unit or the like.
2, if a control unit connected to the data bus can not CLASS2 diagnostic (Tech2) to complete the data exchange, while the other control units communicate properly, it shows that the control unit is faulty or the control unit to the assembly between SP205 data cable break or poor contact (each control unit is connected to the CLASS2 bus through SP205).
3, CLASS2 communication network static voltage is 0V, the voltage enabled to 7V. If the connection of the control unit data bus or data bus diagnostic connection is disturbed, such as a bus or on the ground short of power, will cause all of the control unit can not be normal data communications.
Here I met through the fault case actual repair work to help overhaul maintenance personnel to learn more about the techniques and diagnostic thinking CLASS2.
Case one
Symptom: a 2001 Buick GL sedan, mileage 80,000 km, reflects the owner when the vehicle is traveling on uneven pavement, dashboard instrument lights (warning lights) sometimes all lit after starting the vehicle instrument similar case the self-test, but the engine does not stall.
Troubleshooting: When traveling on a bumpy road, the lights on the dashboard lit up all of a sudden failure believe that some maintenance personnel have encountered, according to the failure phenomenon, first be sure to intermittent electrical fault. For the car, the reasons for this failure may have a meter or meter power line failures have bad place, because the instrument lights corresponding to each system control units are associated with CLASS2 bus, so the bus is also faulty CLASS2 possible.
Performed on uneven pavement road test, when the body undulating, the meter on the dashboard instantly lit lantern, but will soon extinguished, each instrument indicating change slightly. Check with Tech2 instrumentation systems IPC, no fault code, check the connections on CLASS2 bus control units, control units exist within different fault code, indicating a greater likelihood of failure caused by CLASS2 bus.
A vehicle grounding point G200 map
Because of the control unit is connected via SP205 CLASS2 assembly onto the bus, so first check assembly SP205, but found no poor contact. So what factors will affect all control units connected to the bus on CLASS2 it? I think the most likely reason is that the battery voltage, battery voltage when the resistance changes or changes take place, it will affect the data transfer CLASS2 bus.
Fixed at one end of the multimeter plug assembly SP205 A foot, by measuring the voltage on the data line voltage block, and when the engine operating voltage of 7V, normal. To simulate the conditions of a failure, a significant body shaking, sometimes found that the voltage fluctuations. Power generator voltage measurement for 14V, standards-compliant, check the main grounding line, body grounding point G200 (Figure 1) without exception, is located at the transmission housing grounding point G117 / G113 (Figure 2) virtual access, and the obvious signs of a current ablation. Ground line polished and properly fixed, the road test after repeated failures no longer occurred.
Two transmission housing grounding point Figure G117 / 113 virtual access
In the actual repair work, bad circuit Ground fault or poor conduction mostly refers to disconnect the wires connecting the terminals and connecting terminals loose rust and so on. For such a fault, the fault can be found normally by visual inspection, or may be performed to measure the voltage drop measured resistance value. I think, in the detection of CLASS2 bus, if they can use an oscilloscope to observe the waveform CLASS2 on communications data would be very intuitive, and can shorten the repair time.
Ground line is part of the circuit loop, but in many vehicles, a large number of electronic devices rely on a few common grounding wire to pass current, I think this is because the use of a small amount of good quality grounding wire in the circuit (that is the main grounding line) and higher reliability than using multiple grounding lines. Many grounding at both ends of the line also uses a specially shaped grounding wire connection terminals, gaskets and fastening screws, which is given to the grounding line special consideration.
Case II
Symptom: a 2004 Buick GL8 commercial vehicle, mileage 25,000 km, reflects the owner sometimes does not respond when starting the starter, and the anti-theft warning lights, gear indicator is not lit, the other instruments showed no change in the law.
Troubleshooting: Because the car comes to a number of system failures, failures are quite complex, so each first with Tech2 diagnostic system control unit. However, when a fault occurs, the use of the control units can not enter Tech2. I think, though failure phenomenon mainly in the dashboard of each indicator exception, but the possibilities of the instrument lights at the same time very little damage. Gear signal, water temperature signal, speedometer signal, fuel gauge engine tachometer signal and the signal from the power system are a control unit PCM, PCM accept sensor signals and transmitted to the instrument via CLASS2 bus, so the most likely point of failure is PCM or CLASS2 bus.
Figure 3 engine control system wiring diagram
First check the PCM power and grounding lines and found no abnormalities. Disconnect the PCM harness connector on, turn the ignition switch, measure the PCM harness connector C1 on the 59-pin-to-ground voltage of 5V, while CLASS2 static voltage should be about 0V, which shows the existence of the power bus CLASS2 where a short circuit. To narrow the scope of failure, one by one off the assembly line each system data on the SP205, SP205 when disconnected D-foot CLASS2 bus voltage drop 0.6V.
Because D-pin data cable and radio connected, then remove the radio check and found that the radio circuit board traces of corrosion by water, there could be air-conditioned water infiltration. After replacing the radio and air conditioning pipe properly handle nearby car troubleshooting.
Because a radio malfunction CLASS2 bus power supply short circuit, causing the PCM data can not be correctly transmitted to the meter, the meter indication of the cause of the abnormality, but also led to the engine can not start.
Case III
Symptom: a 2003 Buick Regal 2.0 sedans, mileage 30,000 km. Turn the ignition switch, fuel gauge instrument self-test is complete return to zero, the fuel warning light, warning buzzer sound. Start the engine, the starter does not have any reaction.
Failure Analysis: After the fuel level signal transmitted by the level sensor to the power system control unit PCM, after CLASS2 bus transfer to the instrument. When a fault occurs, the fuel gauge return to the zero position, the fuel warning light, warning buzzer sound, these phenomena show that the signal does not reach the fuel meter, probable cause is CLASS2 bus can not communicate with the PCM, should focus on checking CLASS2 bus, PCM, PCM's power cord and grounding lines and other lines. Maintenance process: Use Tech2 check the control unit, PCM internal fault codes exist U1000 (two serial data loss), U1016 (loss of dialogue with PCM), U1064 (loss of dialogue with BCM), these buses can not fault code and instructions CLASS analysis of PCM communication is correct.
Reference engine control system circuit diagram (Figure 3), remove the PCM harness connector on the plug with a test light to detect C1 of the 20th pin, pilot lights. Turn the ignition switch, with a test light to detect C2 of the 24th pin plug, test lights, detect C1 plug in the 19th pin, try lights. When the ignition key is in the starting block, the C2 with a test light to detect the 23-pin connector, test lights. Disconnect the negative terminal of the battery, electrical multimeter to check with a stop pin plug C1 No. 56, No. 57 pins, 60 pins and 16 pins to ground resistance, are in line with standards. Check CLASS2 bus assembly SP205 B pin harness connector to the PCM harness connector C1 of the resistance between the No. 58 pin, standards-compliant, and no plug has bad place. As can be seen from the above examination, the possibility of internal PCM failure is relatively large, so the replacement PCM test, but the fault was not ruled out. The direct use of jumper assembly SP205 B-pin and pin connector No. 58 PCM harness connector C1 in, test the fault persists, but doing so may exclude the possibility of problems in the CLASS2 bus. So the point of failure only PCM power cord and grounding line, or in front of the measurement methods or data is incorrect. Then I found the pilot light is used to test diode test lamp type, such as no-load test lamp type test light, as long as the drive voltage greater than 2V pilot light will light up, the pilot light can not be used to test the line with a fuse cord.
Pilot lights with active load measurements on C1 PCM harness connector of the 19th pin, test light does not shine, which is different from the previous test results. Check the instrument panel to the right of the A7-A8 fuse is not damaged, remove the engine compartment fuse box to check the wiring harness connector pins found in A7 C2 pin plug socket larger. After repairing the wiring harness connector, test troubleshooting.
Review Summary: Since C1 PCM harness connector on the on the 19th pin power cable circuit, resulting in PCM can not communicate with CLASS2 bus, resulting in the car faults, I used an inappropriate test lamp also walked some repair work detours.
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