One of my readers,Chasen share a real repair case to me,and hope I share it on my blog.So I rewrite his e-mail,and then share it here.It is a real repair case about Ford F150 oil service light on,and big shift shock when engaging a gear.
Equiped: V8,6.2L engine,automatic/manually transmission
- Oil service light on the instrument cluster
- Big shift shock when engaging a gear
- You feel it like only have 3 shift when you driving
Because it is a sporadic trouble,so our technicians did not found the problem when testing.And our technician used diagnostic tool to read out the trouble codes:
P0135:Oxygen O2 Sensor Heater Circuit Malfunction(Bank 1,Sensor 1).
P0155:Oxygen O2 Sensor Heater Circuit Malfunction(Bank 2,Sensor 2).
Them mean that it applies to OBD-II equipped vehicles.This code refers to the front oxygen sensor on bank 1 and bank 2.The heated circuit in the oxygen sensor decres time needed to enter closed loop.As the O2 heater reaches operating temperature, the oxygen sensor responds by switching according to oxygen content of the exhaust surrounding it. The ECM tracks how long it takes for the oxygen sensor to begin switching. It the ECM determines (based on coola) that too much time elapsed before the oxygen sensor began operating properly, it will set P0135.
And technicians found other control units work correctly,so them suspected that it maybe transmission control unit received the engine trouble instructions,and entered emergency mode result in oil service light on and shift shock.
Technicians replaced two new Oxygen O2 Sensor,cleared trobule code and found the trobule syptoms disappeared.So asked customer to feedback problem in the next days.But customer came back with the same problem,but different trobule code:
U0100:Lost Communication with ECM/PCM “A”
U0101:Lost Communication with Transmission Control Module.
According to the meaning of these two trouble code it is communication trouble transfer case between PCM,TCM.So technicians prepared to check the wire harness,and unconsciously found the wire harness from engine to transmission was worn,and the it attach to the screw show as below picture
Fix the damaged wire harness,paint the sealant on screws and fix the wire harness under the screws to separate them far away each other forever.