Benz ML500 ESP System Troubleshooting by Star Diagnosis
Mercedes-Benz (year: 2000) MLl500 sport utility vehicle is with mileage of more than 80,000 km. Driving dashboard ESP (Electronic stability control system), ETS (Traction Control System) and ABS (anti-lock braking system) 3 dashboard lights flashed. The car has been examined in the special maintenance station and maintenance staff checked that the problem is the ABS pump. So ABS pumps, a lateral acceleration sensor and the offset rate sensor need to be replaced. The owner thought the repair price is too high, so he comes to the repair shop for checking it.
Firstly I do the fault diagnostic examination withV2015.05 MB SD Connect Compact 4. After inquiring ESP system, I obtained a fault code C1402, meaning a “high reflux pump failure.” According to maintenance experience, there may be parts of the DTC with ABS pump, ESP control unit and associated circuitry. Maintenance personnel are requested to carry out testing ABS pump on another vehicle. We do a road test after clearing fault codes by MB SD Connect Compact 4 Star Diagnosis. When the car was travelled for a short distance, ETS lamp on the instrument panel light up but fault codes we collect still are C1402, which indicates that the problem is not the ABS pump. Mercedes-Benz ML500’s ESP control unit is located in the engine compartment’s fuse box and closed to the engine control unit. For troubleshooting, we reverse ESP control unit in the two vehicles. Since the replacement of the ESP control unit, so first we use MB SD Connect Compact 4 with WIFI to do coding for the control unit and activate the driving test. During the road test ETS lamp still lights up at the start, but the ABS lamp was lit after the start! We retrieve fault codes, DTC C1402 and a fault code C1200 meaning “driving test is activated.” It turned out to be no exit after the driver has completed the test activation. DTC C1200 can not be cleared with MB SD Connect Compact 4 diagnostic tool, so I continued to conduct a trial run. When being unable to do anything, ESP, ETS and the ABS light on the instrument panel are all turned off. What happened? Is it the troubleshooting? To turn off the engine and then turn on the ignition switch, I found the whole fault light on the dashboard does not light up. If I turn off the ignition switch and wait a few minutes and then turn it on, all the fault lamp will light up. When we carefully look at each instrument display, odometer does not show the number of kilometers, the fuel gauge needle turns over 300 degrees and the tachometer needle is not normal! We are surprised. Is it burned when replacing the ESP control unit, or does the meter program disorder? But apparently there is no necessary relation between the two.
In order to make the instrument instruction work, maintenance personnel conducted a number of pass, power test, but to no avail. Then suddenly the owner of the car reflected the meter has been tuned and it is not fine at the 1st time. It is said that the fuel gauge becomes not normal after the installation, and it returns normal after ajustment again. Thus, I decided to do re-instrument calibration. Having found the instrument backup data, I re-write it again by the programming procedures to make each meter reading back to normal.
After the repair process above, we can basically eliminate the problem in the pump ABS and ESP control unit. We find the ABS system schematic, ABS pump A7/3 of the high-pressure return pump M1 with only two cables for one is in the vicinity of the left headlight Ground (W9) and the other one is controlled by the K25 relay. K25 relay has five legs (the 4th pin empty). The 1st and the 2nd foot are connected to the 10th pin and the 12th pin on ESP control unit N47. And the 5th foot is divided into two lines that one is connected to the 11th N47 foot on the ESP control unit and the other is connected to a high-pressure line reflux pump M1. The 3rd foot is connected to the positive supply line. We examine the harness connector on the ABS and ESP pump control unit and measure the relevant line, but find no problems. Because the relay K25 plays an important role for connecting the ESP control unit and M1 reflux pump high-pressure line, so we make replacement of the K25 relay. During the course of the road test, ETS lights and ESP lamp are no longer lit and fault Code C1402 did not reappear. It seems the fault really lies in the relay K25. Next what we need to solve problems of ABS lights lit which is caused by the driving test activated by MB SD Connect C4.
Following the instructions on SD Connect Compact 4 diagnostic tool, we find that if the diagnostic plugs are pulled, the short distance traveling will be closed the activated driving test. But ABS light is still not extinguished when we traveled a long distance. If we carry out in accordance with instructions of the driving test in Mercedes-Benz WIS, ABS lights automatically turn off, and this fault is completely drained.
In order to facilitate the maintenance staff, now a road test standard of the Mercedes-Benz ML is described below.
(1) After replacing the ESP control unit, a lateral acceleration sensor or offset rate sensor in Mercedes-Benz ML cars, maintenance personnel must do calibration and road test learning.
(2) Activation test: It is necessary for maintenance personnel initialize the road test when using MB STAR diagnostic tool to enter Driving test in Control unit adaption.
Note: At this point, whether the ignition switch is in the “ON” or “OFF”, the road test program will be activated and will be stored fault codes C1200 to explain the driving test is activated. This DTC can not be automatically cleared with MB STAR diagnostic System only after a successful road test.
(3) Dynamic test: maintenance personnel need drive at 5 ~ 25km/h speed for moving forward; and after a few minutes, turn to the left or right for uniform circular motion of the vehicle (steering angle is not greater than 360 °)