Changan Ford's sales volume is really good in China. After all, it's also big brother. Its Mondeo is also a relatively respectable car. Its sales volume and reputation are not bad. 
Changan Ford New Mondeo sedan with 165 km mileage, model code CD391, equipped with 2.0T engine and automatic transmission.
Vehicle owner reported that R warning light is always on when ABS, ESP and EP are displayed on car's dashboard.
Fault Diagnosis: After car arrives at store, author considers that car has only about 100 km of mileage and is a new car that has not been used for a long time. Anti-Lock Brake System (ABS) assembly components and likelihood of related with them mechanical damage is relatively high. Low. Therefore, firstly, a system self-test is carried out using a special Ford IDS troubleshooting tool, and a large number of network trouble codes starting with "U" are found, among them in body control module (BCM), instrument panel control (IPC), control unit Parking Assist Control Module (PAM), Power System Control Module (PCM), and Power Steering Control Module (PSCM) store DTC U0121, which means "Lost Communication with ABS Control Module", i.e., these control modules communicate with ABS at same time, control unit has lost network communication. During second step of IDS network test, network communication with ABS control unit was also not possible.
After a preliminary analysis of contents of above fault codes, it is believed that possible causes of fault include following points.
(1) ABS control unit power and ground circuit failure.
(2) Network communication circuit failure.
(3) The ABS control unit itself is defective.
According to principle of maintenance "from simple to complex, from outside to inside", author first of all pays attention to checking health of power terminal of ABS control unit and good contact of ground terminal. Refer to anti-lock brake system (ABS) wiring diagram.
Referring to diagram, measure voltage of fuses F82, F69 and F25 in battery fuse box (BJB) corresponding to terminals 1, 30 and 35 on connector C135 of ABS control unit and measure result. that power supply is OK. Then measure ground of terminal No. 14 on ground terminal C135 of ABS control unit connector, ground is also normal. Therefore, ABS control unit assembly was replaced, but after replacement, malfunction remained. On this, repair work stalled.
The author breaks down ideas, by analyzing fault codes, ABS control unit has been replaced and fault persists, and target of fault is still locked in anti-lock brake system (ABS) communication line, so ABS control unit is powered and assembled.
The author uses a powerful light bulb as a test lamp to measure load of ABS control unit power supply to diagnose presence of poor contact of power line (virtual power), and measurement results show that power supply of three power supply terminals is reliable. Is problem still with ground terminal #14? Then disconnect connector C135 and also use a high power test light to make a basic measurement at earth terminal no. 14. Using wiring diagram and service manual I found position of earth point G102.
When checking a powerful lamp, ask an assistant to shake G102 ground point harness and lamp will suddenly flash. This phenomenon indicates poor contact G102 and, finally, main cause of malfunction. found! It turned out that ABS control unit was not properly grounded, which led to abnormal power to ABS control unit, resulting in a communication failure. Troubleshooting: Re-sand G102 ground wire connector and tighten ground point bolts. Reinstall ABS control unit, use IDS to reset DTC, and perform self-test and network test on system again, and communication between anti-lock braking system (ABS) and other control units will be normal. After several road tests of vehicle, corresponding signal lamps no longer illuminated and fault was corrected. Brief description of fault: Since this car is new, problem of virtual connection of earth point of line is not given enough attention, which leads to a maintenance dilemma. From this fault, we can understand that poor line contact is a common problem not only in older cars, but also in new cars, since production process in new car assembly shops can also cause poor line contact problems.
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