A faulty second gear pressure switch inside the transaxle valve body, which is the most common cause on higher-mileage Mazdas.; Damaged, chafed, or corroded wiring in the second gear switch circuit between the transaxle and the TCM.; A loose or contaminated electrical connector at the transaxle solenoid pack or at the TCM.; Low or degraded automatic transaxle fluid (ATF) causing erratic switch operation and poor hydraulic pressure.; A sticking or worn valve body causing incorrect hydraulic pressure at the second gear switch port.; A failing TCM that misreads a valid switch signal, though this is far less common than switch or wiring faults.; Internal transaxle mechanical wear that prevents second gear from fully engaging, so the switch never confirms the shift.

DTC codes / Mazda codes / P1736

P1736 · MazdaSecond Gear Switch Circuit Failure

Q: What does code P1736 mean?

Second Gear Switch Circuit Failure. P1736 on a Mazda means the transmission control module (TCM) has detected an unexpected signal from the second gear switch circuit, which is a pressure switch inside the automatic transaxle that confirms when second gear is engaged. The TCM compares this switch signal with the commanded gear and other sensor inputs, and it sets the code when the circuit voltage stays outside the expected range or does not change when second gear is requested.

P1736 on a Mazda means the transmission control module (TCM) has detected an unexpected signal from the second gear switch circuit, which is a pressure switch inside the automatic transaxle that confirms when second gear is engaged. The TCM compares this switch signal with the commanded gear and other sensor inputs, and it sets the code when the circuit voltage stays outside the expected range or does not change when second gear is requested.

SystemPowertrain

Code typeMazda specific

SeverityMedium

Fix difficultyProfessional

AreaTransmission

Symptoms you may notice

The check engine light or automatic transaxle warning light illuminates on the dashboard.
Often no symptoms besides the warning light, especially if the fault is intermittent.
Harsh or delayed shifts, particularly the 1-2 and 2-3 shifts, as the TCM may default to a fail-safe shift strategy.
The transmission may stay in a single gear or refuse to downshift when coming to a stop.
A noticeable flare or slip when the transaxle attempts to engage second gear.
Reduced fuel economy and higher engine rpm at highway speed if the transaxle holds a lower gear.

Common causes, most likely first

A faulty second gear pressure switch inside the transaxle valve body, which is the most common cause on higher-mileage Mazdas.
Damaged, chafed, or corroded wiring in the second gear switch circuit between the transaxle and the TCM.
A loose or contaminated electrical connector at the transaxle solenoid pack or at the TCM.
Low or degraded automatic transaxle fluid (ATF) causing erratic switch operation and poor hydraulic pressure.
A sticking or worn valve body causing incorrect hydraulic pressure at the second gear switch port.
A failing TCM that misreads a valid switch signal, though this is far less common than switch or wiring faults.
Internal transaxle mechanical wear that prevents second gear from fully engaging, so the switch never confirms the shift.

How to diagnose and fix it

Check the automatic transaxle fluid level and condition first, and top up or service the fluid if it is low, dark, or burnt.
Inspect the wiring harness and connectors at the transaxle and TCM for chafing, corrosion, or loose pins, and repair as needed.
Use a scan tool to read live data for the second gear switch status while commanding or test-driving through the 1-2 shift to confirm the signal is erratic.
Perform a resistance and voltage test on the second gear switch circuit at the transaxle connector to isolate a switch fault from a wiring fault.
If the switch tests out of specification, replace the second gear pressure switch, which on many Mazda transaxles requires removing the valve body.
Clear the code and perform a relearn or adaptation drive cycle, then verify the code does not return during a full upshift and downshift sequence.
If the fault persists after switch and wiring repairs, diagnose the valve body and TCM, and repair or replace the faulty component.

What the second gear switch really tells you

The second gear switch is a confirmation switch, not a shift solenoid, so a P1736 does not mean the transaxle cannot physically engage second gear; it means the TCM cannot verify that it did.
A common misdiagnosis is replacing the shift solenoids or the entire valve body when the actual fault is a chafed wire near the transaxle connector that only breaks contact when the engine moves under load.
Low or burnt automatic transaxle fluid often sets this code on Mazdas because the switch relies on clean, correctly pressurized fluid to actuate, so a fluid service can resolve the fault before any parts are replaced.
An intermittent P1736 that appears only on cold mornings frequently traces to a failing pressure switch that has not yet failed completely, so live data during a cold test drive is more useful than a static resistance check.
A failing TCM can mimic a switch fault by misreading a good signal, so always verify the switch and wiring at the transaxle before condemning the module.

Can I keep driving with P1736?

You can usually drive the vehicle to a repair shop, but avoid heavy acceleration and highway merging because the transaxle may be in a fail-safe mode with harsh or missing shifts. If the transmission slips badly or refuses to engage gears, stop driving and have it towed to prevent internal 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.