DTC P0721 Non-European or N. American Emissions
Circuit Description
The vehicle automatic transmission (A/T) output shaft speed (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. 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 increasing rate of the output speed is more than 45,000 RPM/second. |
| • | System voltage is greater than 8.5 volts. |
| • | The engine is running. |
| • | Output speed is greater than 9,762 RPM. |
| • | No park/neutral position switch error DTC P0705 is set. |
| • | The TCM or engine control module (ECM) is defective. |
Action Taken When the DTC Sets
| • | The hold lamp will blink. |
| • | The TCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Failure Records buffer. |
| • | Adopt Emergency/Substitute mode and constant 4th gear. |
| • | Open the lock-up clutch. |
Conditions for Clearing the Hold Lamp/DTC
| • | The hold lamp 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. |
| • | Using a scan tool can clear history DTCs. |
Diagnostic Aids
When DTC P0721 sets, the possible cause of fault could be the output speed sensor.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform 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 value? | ∞ ohms | Go to Step 9 | Go to Step 4 |
4 |
Is the resistance within the specified value? | 0 ohms | Go to Step 6 | Go to Step 5 |
5 | Repair the malfunctioning terminals as necessary. Did you complete the repair? | -- | 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. Did you complete the repair? | -- | System OK | -- |
8 | Replace the input speed sensor. Did you complete the replacement? | -- | System OK | -- |
9 |
Is the resistance within the specified value? | 0 ohms | Go to Step 11 | Go to Step 10 |
10 | Repair the malfunctioning terminals as necessary. Did you complete the repair? | -- | 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. Did you complete the repair? | -- | System OK | -- |
13 | Replace the TCM. Refer to Transmission Control Module Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- |
14 |
Are there any DTCs that have not been diagnosed? | -- | Go to Step 2 | System OK |
DTC P0721 European and N. American Emissions
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/second. |
| • | The system voltage is greater than 8.5 volts. |
| • | The engine is running. |
| • | DTCs P0705, P0725, and P0727 are 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 the 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 fault could be the OSS.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform 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 value? | ∞ ohms | Go to Step 9 | Go to Step 4 |
4 |
Is the resistance within the specified value? | 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 specified value? | 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 |
