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DTC codes / Ford codes / P1720

P1720 · FordVehicle Speed Meter Circuit Malfunction

P1720 on a Ford vehicle means the powertrain control module (PCM) has detected an abnormal signal from the vehicle speed sensor (VSS) circuit, which it uses to calculate road speed. The PCM monitors the VSS signal and sets this code when the voltage or pulse pattern falls outside the expected range for the current operating conditions.

SystemPowertrain
Code typeFord specific
SeverityMedium
Fix difficultyIntermediate
AreaTransmission

Symptoms you may notice

  • Speedometer needle may stay at zero, jump erratically, or read incorrectly while driving
  • Transmission may shift harshly or at the wrong points because the PCM lacks accurate speed data
  • Cruise control may fail to engage or disengage unexpectedly
  • Anti-lock braking system (ABS) warning light may illuminate on vehicles that share the speed signal
  • Often no symptoms besides the warning light, especially if the fault is intermittent
  • Odometer may stop accumulating mileage or accumulate it incorrectly

Common causes, most likely first

  1. Faulty vehicle speed sensor (VSS) on the transmission or rear axle
  2. Damaged or corroded wiring and connectors between the VSS and the PCM
  3. Failed or contaminated speedometer head or instrument cluster on models where the VSS signal passes through it
  4. Damaged tone ring or reluctor wheel that the sensor reads
  5. Poor ground connection at the sensor or PCM
  6. PCM internal fault affecting the VSS input circuit (rare but possible)

How to diagnose and fix it

  1. Connect a scan tool and read live vehicle speed data to confirm whether the PCM is receiving any speed signal
  2. Inspect the VSS and its connector for physical damage, corrosion, or loose pins
  3. Check the sensor's resistance and AC voltage output while spinning the wheels or driving, following Ford service information for the specific model
  4. Perform a voltage drop test on the sensor ground and signal wires to rule out high resistance
  5. Inspect the tone ring or reluctor wheel for missing teeth, cracks, or debris
  6. If the sensor and wiring test good, check the instrument cluster and its connections on models where the speed signal is routed through it
  7. Clear the code and road-test the vehicle to verify the repair and confirm the code does not return

What Ford techs check before replacing the VSS

  • A common misdiagnosis is replacing the VSS when the real problem is a worn tone ring or a corroded connector that interrupts the signal only over bumps.
  • On many Ford models the VSS signal is shared with the ABS module, so a fault in the ABS system can set P1720 even when the VSS itself is fine.
  • Aftermarket stereos or alarm installations that tap into the speed signal wire can introduce noise or a short that triggers this code.
  • A weak battery or charging system fault can cause erratic sensor signals and set P1720 intermittently, so always verify system voltage first.
  • The code can be stored by a momentary glitch during engine cranking if the battery is low, and it may not indicate a hard failure.

Can I keep driving with P1720?

You can usually drive the vehicle, but expect inaccurate speedometer readings and potentially erratic transmission shifting, so avoid sustained high-speed driving and towing until the fault is repaired. If the transmission begins shifting harshly or the vehicle enters limp mode, stop driving and seek professional diagnosis.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for Ford vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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