Circuit Description
The vehicle automatic transmission (A/T) output speed sensor (OSS) is a magnetic inductive pickup that relays information relative to vehicle speed to the transmission control module (TCM).
Vehicle speed information is used by the TCM to control shift timing, line pressure, and torque converter clutch (TCC) apply and release.
The output speed sensor mounts in the case at the speed sensor rotor, which is pressed onto the spur gear. An air gap of 0.1-1.3 mm (0.004-0.05 in) is maintained between the sensor and the teeth on the spur gear teeth. The sensor consists of a permanent magnet surrounded by a coil of wire. As the differential rotates, an AC signal induces a higher frequency and voltage measurement at the sensor. The sensor resistance should measure infinity at 20°C (68°F). The sensor can measure from 20-8,000 hertz.
Conditions for Setting the DTC
| • | The transmission speed is less than 8,160 RPM. |
| • | The increasing rate of output speed is more than 45,000 RPM/seconds. |
| • | The system voltage is greater than 8.5 volts. |
| • | The engine is running. |
| • | DTCs P0705, P0725 P0725,and P0727are not set. |
| • | The TCM or engine control module (ECM) is defective. |
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate. |
| • | The TCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Failure Records buffer. |
| • | The running vehicle remains in actual gear. |
| • | Open lock up clutch |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF when the malfunction has not occurred after 3 ignition cycles. |
| • | A history DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | Clear the DTCs with a scan tool. |
Diagnostic Aids
When DTC P0721 sets, the possible cause of the fault could be the output speed sensor (OSS).
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform an the Diagnostic System Check-Automatic Transmission? | -- | Go to Step 2 | |
2 |
Is the speed within the specified range? | 190-9,762 RPM | Go to Diagnostic Aids | Go to Step 3 |
3 |
Is the resistance within the specified range? | ∞ ohms | Go to Step 9 | Go to Step 4 |
4 |
Is the resistance within the specified values? | 0 ohms | Go to Step 6 | Go to Step 5 |
5 | Repair the malfunctioning terminals, as necessary. Is the action complete? | -- | System OK | -- |
6 |
Is the voltage within the specified range? | 11-14 V | Go to Step 7 | Go to Step 8 |
7 | Repair the malfunctioning terminals, as necessary. Is the action complete? | -- | System OK | -- |
8 | Replace the output speed sensor. Is the action complete? | -- | System OK | -- |
9 |
Is the resistance within the values shown? | 0 ohms | Go to Step 11 | Go to Step 10 |
10 | Repair the malfunctioning terminals, as necessary. Is the action complete? | -- | System OK | -- |
11 |
Is the voltage within the specified range? | 11-14 V | Go to Step 12 | Go to Step 13 |
12 | Repair the malfunctioning terminals, as necessary. Is the action complete? | -- | System OK | -- |
13 | Replace the TCM. Refer to Transmission Control Module Replacement . Is the action complete? | -- | Go to Step 14 | -- |
14 |
Did the last test fail or is the current DTC displayed? | -- | Go to Step 2 | System OK |
