Problem: This vehicle was brought to the
shop because the malfunction indicator lamp was on. The customer
also mentioned that the engine would hesitate when she shifted
the transmission into reverse.
The technician connected a scan tool and retrieved a P0705 -
Transmission Range Sensor A (TRS) diagnostic trouble code (DTC).
He replaced the TRS and tried to clear the DTC, but it would not
erase. When he called ALLDATA Tech-Assist, the consultant
suggested checking for moisture or water intrusion in either or
both taillights and to pay close attention to the back-up lamp
The technician checked the taillights, he found a large amount of
moisture in both. He called the ALLDATA Tech-Assist consultant to
report what he had found and to ask what the connection was
between the back-up lamps and the TRS.
The Tech-Assist consultant explained that, as you switch between
gears, 12V battery power flows back to the transmission control
module (TCM) to tell the module which gear was chosen. However,
since the TRS also supplies power to the backup lamp circuit, the
TCM is expecting to see a large voltage drop on the reverse
signal control wire (should be slightly above zero volts).
All other lights are controlled by the body control module, but
the back-up lights are powered directly through the TRS. If
there’s corrosion in the taillight assemblies, the TCM will see
higher voltage on the reverse signal line and set a P0705 DTC. It
is recommended by the manufacturer that, if you see any signs of
water or moisture, check the circuit boards and light bulb
sockets for corrosion. If corrosion is present, replace the
taillight assemblies, clear the DTC and see if the engine
hesitation goes away when shifted into reverse.
Confirmed Repair: The tech found corrosion
in both reverse lamp sockets and some on one of the circuit
boards, so he replaced both lamp assemblies. After the repair he
was able to clear the P0705 DTC. When shifting into reverse, the
engine hesitation was gone. After a good test drive, the DTC did
not return. Fixed!