OBD-252
On-Board Diagnostics
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DTC P0717 Turbine Speed Sensor Circuit No Signal (Figure OBD-70)
Figure OBD-70: Turbine Speed Sensor Circuit
Circuit Description
The speed sensors are variable reluctance devices that convert mechanical motion to an AC voltage. Each sensor consists of a wire
coil wrapped around a pole piece that is adjacent to a permanent magnet. These elements are contained in a housing that is mounted
adjacent to a rotating ferrous member, such as a gear tooth. Two signal wires extend from one end of the housing and an exposed
end of the pole piece is at the opposite end of the housing. The permanent magnet produces lines of flux around the pole piece. As
a ferrous object, such as a gear tooth, approaches and passes through the gap at the end of the pole piece, an AC voltage pulse is in-
duced in the wire coil. The transmission control module (TCM) calculates the frequency of these AC pulses and converts it to a
speed value. The AC voltage generated varies from 150 millivolt at low speed to 15 volts at high speed. The signal wires from the
sensor are formed as twisted pairs to cancel magnetically induced fields. The cable is also shielded to protect from voltage-related
fields. Using two-wire differential inputs at the TCM eliminates noise from other sources.
DTC P0717 is a type A DTC.