ZF 4HP 16 - Automatic Transmission (Non-European or N. American Emissiion)

DTC P0721 (Non-European or N. American Emissiion)

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.