Case of Man Engines Poor acceleration fault Phenomenon and analysis

MAN Vehicle mode: MAN
Date of manufacture: June, 2000
Driving : 645201KM
VIN: WMAT31ZZZYM303495

Fault phenomenon:
This vehicle driving powerless, engine unable to accelerate, EDC light on.
Fault diagnosis: This vehicle is electronic control system, to detect with Fcar auto scanner, connect testing cable to test head and main unit respectively,(diagnostic plug is above relay box besides center console)

? ??In the case of without 37-pin diagnostic connector, you can use jumper box to connect and diagnose. Jumper method see table 1, connect testing cable respectively with jumper box and main unit. Turn ignition switch to ON gear position, switch on power switch of Fcar scanner. Entry to menu ?Diesel?—?MAN?—?V5.3?—?BOSCH EDC MS5/M(S)5?—?Read DTC?,Fault display ”87 intake pressure sensor fault” ”85 coolant temperature sensor fault” ?Clear DTC?display “System clear success” in?Read DTC?“87 intake pressure sensor”“85 coolant temperature  sensor” appear again, DTC cannot be cleared.
Select menu?Read data stream? on menu and click to enter and check(Readout data see Table 2). Analyze the specific faulty part together with data stream.
Name Jumper box jack label Diagnostic socket label Diagnostic socket voltage V
Positive VCC A 24V
Negative GND D 0V
Signal K 15 Z 23V
Signal L 7 a 23V
Table 1 Connection of Jumper box with car diagnostic socket

Fault Analysis
To analyze according to reading data stream, the vehicle engine still cold water temperature sensor data stream is 95 degrees, the intake pressure sensor data 120kPa. Start the engine, after idle for some time no change in water temperature data, depresses the accelerator pedal to increase engine speed, view the data stream, intake air pressure sensor data is still 120kpa unchanged, indicating that the water temperature sensor and intake air pressure sensor data is abnormal (see data stream of this vehicle in Table 2, Table 3 is data stream that has some changes), initially judge water temperature sensor and intake air pressure sensor part is defective.

Check water temperature sensor and intake air pressure sensor, both of which were found abnormal, to be replaced.

Sensor name High speed Idle Static
Water temperature sensor° 95 95 95
Inlet pressure sensor kpa 120 120 120
Engine speed rpm 1900 730 0
Table 2 data stream of this vehicle
Sensor name High speed Idle Static
Water temperature sensor ° 85 85 28
Inlet pressure sensor kpa 600 200 100
Engine speed rpm 1900 730 0

Table 3 changed data stream              
Troubleshooting
? ?Replace water temperature sensor see Pic.2,inlet pressure sensor see Pic.3.Use menu on Fcar scanner menu to clear DTC, display clear success; Read DTC again, system normal; road test, fault disappear, completely remove fault.

Posted by fcars on Tue, 07/15/2014 - 7:47pm