One of my regular customers drove his VW Bora to our garage,and ask technicians to solve his trouble:fuel gauge and display interface trouble.Here I share this repair progress on VW Bora fuel gauge and display interface trouble.
Vehicle info:
Model: VW Bora
Engine: BJH
Mileage: about 20,000 miles
Trouble description:
Vehicle display interface multi-function menu can not operate
Fuel gauge can’t display the fuel value
Trouble diagnosis:
Use diagnostic to detect the DTCs,there are two DTCs:
00771:Fuel Level Sensor (G):Open/Short Circuit
Possible Symptoms:Fuel reserve displayed value 0 (empty)
Possible Causes:Fuel Level Sensor (G) damaged
1 Wiring between Fuel Level Sensor (G) and Instrument Cluster: Open or Short Circuit
2 Fuel Level Sensor (G) damaged
01039:Engine Coolant Temperature Sensor (G2)
Possible Symptoms:
Difficulties with starting a cold engine.
Starting the engine when engine is warmish or warm, idle rpm immediately is 1200 – 3000 rpm.
RPM at idle is irregular.
With all engine temperatures seldom idle rpm will vary between 900 – 1000 rpm.
With engine warm (90 °C) the engine temperature suddenly drops (70 °C) and slowly comes back to 90 °C.
Bad acceleration during warming up.
Diesel: an indication is extreme long time burning time of the glow indication light.
Possible Causes:
Wiring and/or connections faulty
Engine Coolant Temperature Sensor (G2) faulty
Turn off the ignition,detect fuel gauge sensor G and Coolant Temperature Sensor G2
1. Measure the resistance value of G sensor between pin 2 and pin 3,it showed 35Ω (normal,full fuel tank)
2. Measure the resistance value of G2 sensor between pin 1 and pin 2,it showed 30005(normal,engine normal temperature)
Remove combination instrument to check the instrument cable:
Measure the resistance value between T32/7 and T32/5,and check the appearance of the harness wire–normal.
Measure the resistance value T32/8 and 1# wire of G2—normal (Figure 1)
Check the GND
Contrast the circuit diagram(figure 2),the #269 node in the instrument harness is the common junction of the fuel level sensor G,coolant level sensor G32,coolant temperature sensor G2,outdoor temperature sensor G17 and switch E multi-function
Display.Through the T32 / 7 in the J285 control unit with the display of the internal ground, and finally through the 608 ground in the middle of the windshield drain, check the 608 ground point normal (circuit diagram in Figure 3).
Measure voltage of instrument harness
Turn on the ignition,measure voltage between T32/7 and GND,it showed 13v,the GND of all instrument harness 269 node showed 13v.Disconnect the Fuse S11,all sensor ground no longer live.And the resistance value was 5012Ω between T32/1 and T32/7,it mean short circuit.
Check the instrument harness:
Remove the instrument and found the instrument harness was damaged.The wires of 269 node was squeezed by the dashboard,and it result in short circuit and instrument internal circuit burnout.
Solution:
Rebandage the 269 node wires,replaced a new instrument cluster.