The vehicle speed sensor signal/data is collected from the ‘combination meter’ (i.e. gauge cluster/speedometer), then transmitted to the TCM via the CAN bus communication line. A P1721 OBDII code indicates that there is a problem with the data transmission signal.
How Serious is the Code?
A P1721 diagnostic trouble code isn’t likely to leave you stranded on the side of the road. However, it can cause mild inconveniences like a malfunctioning speedometer and harsh shifting.
Symptoms of a P1721 include:
- Malfunctioning speedometer
- Harsh shifting
- Damaged wiring or connectors
- Failed TCM communication line
How to Diagnose the Code?
When diagnosing a P1721 Nissan OBD2 code, the first thing that should be done is to check the condition of the wiring and connectors between the gauge cluster and the transmission. The CAN bus lines should also be checked for signs of damage and corrosion.
What Repairs Will Fix P1721?
- Repair damaged wiring and/or connectors