Faulty throttle position sensor; Damaged or corroded wiring or connector at the TP sensor; Open or short circuit in the TP sensor signal circuit; Poor ground connection for the TP sensor; PCM internal fault (less common); Contamination or mechanical wear inside the throttle body affecting sensor operation

DTC codes / Mazda codes / P1791

P1791 · MazdaTP Electric Circuit

Q: What does code P1791 mean?

TP Electric Circuit. P1791 on Mazda vehicles indicates that the powertrain control module (PCM) has detected an electrical fault in the throttle position (TP) sensor circuit, which may involve an open, short, or abnormal voltage signal. The PCM monitors the TP sensor signal and sets this code when the voltage falls outside the expected range or is inconsistent with other load signals.

P1791 on Mazda vehicles indicates that the powertrain control module (PCM) has detected an electrical fault in the throttle position (TP) sensor circuit, which may involve an open, short, or abnormal voltage signal. The PCM monitors the TP sensor signal and sets this code when the voltage falls outside the expected range or is inconsistent with other load signals.

SystemPowertrain

Code typeMazda specific

SeverityMedium

Fix difficultyIntermediate

AreaTransmission

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
Hesitation or stumble during acceleration
Erratic or surging engine speed while driving
Reduced engine power or limp mode
Poor fuel economy or increased emissions
In rare cases, the engine may stall or fail to start

Common causes, most likely first

Faulty throttle position sensor
Damaged or corroded wiring or connector at the TP sensor
Open or short circuit in the TP sensor signal circuit
Poor ground connection for the TP sensor
PCM internal fault (less common)
Contamination or mechanical wear inside the throttle body affecting sensor operation

How to diagnose and fix it

Inspect the TP sensor connector and wiring for corrosion, damage, or loose pins
Check the TP sensor reference voltage and ground circuits with a multimeter
Measure the TP sensor signal voltage while slowly opening the throttle to check for smooth operation
Compare TP sensor readings with a scan tool to verify consistency with pedal position
Repair or replace damaged wiring or connectors as needed
Replace the throttle position sensor if it fails electrical testing
Clear the code and perform a road test to confirm the repair

TP Sensor Circuit Checks Before Replacement

A sticking or carbon-fouled throttle body can cause the TP sensor to report implausible values, setting P1791 even when the sensor itself is good.
Intermittent wiring faults often appear only when the engine is hot or vibrating, so wiggle-test the harness while watching live data.
Some Mazda models use a drive-by-wire system where the TP sensor is integrated into the throttle body, making replacement more costly than a standalone sensor.
A weak battery or poor charging system voltage can cause false TP sensor codes, so always verify battery and ground integrity first.
P1791 can be set by a faulty accelerator pedal position sensor on some models, as the PCM cross-checks both signals.

Can I keep driving with P1791?

You can usually drive the vehicle with P1791, but expect reduced performance and possible limp mode; avoid aggressive acceleration and have the fault diagnosed promptly to prevent stalling or further damage.

Tools that help

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