P1720
Vehicle Speed Sensor 2 Signal Error.
- Mazda
- Powertrain
- Manufacturer code
- Medium severity
How this code is built
- P
- SystemPowertrain
- 1
- Defined byThe manufacturer
- 7
- AreaTransmission
- 20
- FaultThe specific fault in that area
What it means
On a Mazda, P1720 means the powertrain control module has detected a fault in the signal from vehicle speed sensor 2. The module compares the speed signal with other inputs such as engine speed, load and the main speed signal, and has seen a missing, erratic or implausible reading. How the second speed signal is generated and used (transmission output speed, ABS wheel speed or a separate sensor) depends on the model and gearbox.
Symptoms
- Warning light on (engine management and possibly gearbox warning)
- Speedometer reading erratic, lagging or not working
- Harsh, delayed or poorly timed gear changes on automatic models
- Transmission stuck in one gear (limp mode) on some automatics
- Cruise control not working
- Unstable idle or poor engine response when slowing or stopping
Possible causes
- Faulty vehicle speed sensor 2 or its reluctor/pickuplikely
- Damaged wiring, chafed loom or poor connector contact in the speed sensor circuitlikely
- Metal debris or contamination on the sensor tip or a damaged tone wheelpossible
- Low or contaminated transmission fluid affecting sensor or gearbox operation (automatics)possible
- Fault in the ABS wheel speed input or ABS module, if the signal is shared on that modelpossible
- Faulty instrument cluster or powertrain control modulerare
How to diagnose
- Read all stored and pending codes and the freeze frame data, noting vehicle speed, gear and engine load when the code set. Check for related ABS or gearbox codes.
- Compare the scan tool live data for vehicle speed from the engine, ABS and gearbox, and the speedometer, on a road test or with the drive wheels safely raised.
- Visually inspect the sensor, its wiring and connector for damage, corrosion, water ingress, chafing or heat damage.
- Check the transmission fluid level and condition on automatics, following the manufacturer's procedure for the model.
- Remove the sensor and check the tip for metal debris and damage, and inspect the reluctor or tone wheel where accessible.
- Test the sensor circuit for supply, earth, signal continuity and short circuits against the wiring diagram for the model.
- Check the sensor output with a multimeter or oscilloscope while the wheels or output shaft turn, comparing it with the specification.
- Check for relevant technical service bulletins or software updates for the model, then clear the code and retest.
How to fix
- Replace the faulty speed sensor 2 and refit with the correct seal and torque.
- Repair or replace damaged wiring and clean or replace corroded connectors.
- Clean debris from the sensor and replace a damaged tone wheel or reluctor.
- Correct the transmission fluid level or replace contaminated fluid using the specified type.
- Repair the ABS wheel speed sensor or module fault if the shared signal is the cause.
- Update the powertrain control module calibration only if the manufacturer lists an outdated calibration as a known cause.
Can I keep driving?
The car can usually be driven carefully for a short time, but fix it soon. If the gearbox is in limp mode, shifting is harsh or the speedometer is unreliable, limit driving as the fault may worsen and affect safe operation.
Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.