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DTC codes / Nissan codes / P1791

P1791 · NissanTP Electric Circuit

P1791 on Nissan vehicles indicates that the Transmission Control Module (TCM) has detected an electrical fault in the Throttle Position (TP) sensor circuit, which it uses to manage shift quality and line pressure. The TCM monitors the TP signal for expected voltage or rationality and sets this code when the signal is out of range, intermittent, or missing.

SystemPowertrain
Code typeNissan specific
SeverityMedium
Fix difficultyIntermediate
AreaTransmission

Symptoms you may notice

  • Harsh or delayed transmission shifts, especially during acceleration
  • Transmission may enter limp mode and stay in a single gear
  • Poor fuel economy or sluggish engine response
  • Often no symptoms besides the warning light
  • Intermittent shifting problems that come and go
  • Possible stalling or rough idle if the TP signal is erratic

Common causes, most likely first

  1. Faulty Throttle Position sensor or its connector
  2. Damaged or corroded wiring between the TP sensor and TCM
  3. Poor electrical ground at the TCM or sensor
  4. Failed TCM (less common)
  5. Contamination or wear inside the TP sensor
  6. Aftermarket throttle body or sensor with incorrect resistance

How to diagnose and fix it

  1. Scan all modules for stored codes and freeze-frame data to confirm P1791 is active
  2. Inspect the TP sensor connector and wiring for corrosion, chafing, or loose pins
  3. Measure TP sensor reference voltage and signal voltage with a multimeter, comparing to Nissan specifications
  4. Check continuity and resistance of the TP signal circuit from sensor to TCM
  5. Verify TCM grounds and power feeds are clean and tight
  6. Replace the TP sensor or throttle body if signal is erratic or out of range
  7. Clear codes and perform a throttle position relearn or idle air volume relearn if required

TP sensor faults that mimic transmission problems

  • A dirty or worn TP sensor can cause harsh shifting without setting an engine code, so technicians often misdiagnose the transmission itself.
  • The TCM may use a redundant throttle signal from the Accelerator Pedal Position (APP) sensor; a mismatch between the two can trigger P1791 even when the TP sensor tests fine.
  • After replacing the throttle body or TP sensor on a Nissan, a throttle position relearn procedure is often required to prevent the code from returning.
  • Intermittent P1791 can be caused by a loose ground bolt on the intake manifold or engine block, which affects both TP sensor and TCM reference voltages.
  • This code does not always mean the TP sensor is bad; wiring harness damage near the throttle body or TCM connector is a common hidden cause.

Can I keep driving with P1791?

You can usually drive the vehicle to a repair shop, but avoid aggressive acceleration and highway speeds because the transmission may shift harshly or enter limp mode. If the vehicle stalls or refuses to shift, stop driving and have it towed.

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 Nissan vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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