Allison Automatic Transmission
ALLISON AUTOMATIC TRANSMISSION
DTC P0716
Circuit Description for Allison Automatic Transmission
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 induced 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 P0716 is a type A DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0716 Input Speed Sensor Performance
Conditions for Running the DTC
^ DTC P0717, P0721 and P0722 are not active.
^ The components are powered and ignition voltage is greater than 9.0 volts and less than 18 volts.
^ Engine speed is greater than 200 RPM and less than 7,500 RPM for 5 seconds.
^ The turbine speed is greater than 200 RPM.
Conditions for Setting the DTC
DTC P0716 sets when the TCM detects a large unrealistic change in turbine speed or if excessive noise is present in the turbine speed sensor circuit.
Action Taken When the DTC Sets
^ The TCM illuminates the malfunction indicator lamp (MIL).
^ When failure occurs in a forward range and shifting is complete, the transmission remains in the current range. When failure occurs while in a forward range and the shift is in process, the transmission returns to the previous range, except in post-shift state, where the transmission will continue the commanded range. When failure occurs in other conditions, the transmission shifts to 1st, 3rd or 5th. While diagnostic response is active, if the shift selector is moved to NEUTRAL or REVERSE or is selecting DRIVE again, then the transmission will lock in NEUTRAL.
^ DTC P0716 will be stored in TCM history.
^ The TCM inhibits torque converter clutch (TCC) engagement.
Conditions for Clearing the DTC
A scan tool can clear the code from TCM history. The TCM automatically clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without failure.
Diagnostic Aids
^ Inspect the wiring for poor electrical connections at the TCM. Inspect for the following conditions:
- A bent terminal
- A backed-out terminal
-A damaged terminal
- Poor terminal tension
- A chafed wire
- A broken wire inside the insulation
^ When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.
^ You may have to drive the vehicle in order to experience a condition.
^ If the condition is intermittent, connect the scan tool and select the speed sensor indicated by the code. If the signal is erratic, investigate and eliminate the following:
- Intermittent wiring connection
- Excessive vibration, such as driveline or engine torsionals
- Irregular sensor gap, such as a loose sensor, a loose tone wheel or a damaged tone wheel
- Inspect that the speed sensor wiring consists of twisted pairs at the rate of 12-16 twists per 300 mm (12 inch). These twists must extend the entire length of the wiring harness to within at least 50 mm (2 inch) of the speed sensor connector.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. This step tests ignition voltage.
3. This step tests the wiring harness for opens/shorts.
4. This step tests turbine speed sensor resistance.