P0731 on Mercury
Gear 1 Incorrect Ratio
P0731 on Mercury vehicles indicates gear 1 incorrect ratio. Au7o has documented this code across 1 Mercury model — most commonly on Cougar. This code means the Transmission/Powertrain Control Module detected an incorrect gear ratio in 1st gear. The module compares input (engine/turbine) speed to output shaft speed; when the car is commanded into 1st but the calculated ratio doesn't match the expected value, P0731 sets. This points to slipping, an incorrect shift, or a hydraulic/mechanical problem rather than just an electrical fault. You may feel slipping, harsh or delayed engagement, or the transmission may go into a limited 'limp' mode.
Common Causes of P0731
- •Low or degraded/burnt transmission fluid
- •Slipping clutch packs or worn friction components
- •Stuck or faulty shift solenoid affecting 1st gear
- •Internal hydraulic leak / valve body fault
- •Worn or failing torque converter
- •Faulty input or output speed sensor
- •Mechanical wear (planetary gears, bands) inside the transmission
P0731 on Mercury by Model
Mercury Cougar(1 issue)
- CD4E Automatic Transmission Failure (8th Gen)1999-2002
NHTSA communications establish several distinct CD4E conditions on 1999-2002 Cougar vehicles: no-forward engagement in 605229 and 6091763, 1999 ring-gear side loading of the forward-clutch snap-ring retainer in 607645, intermittent loss of first and second gears with P0758 or P0740 in 619324, and harsh or delayed shifts after speed-sensor service in 630631. These records support the generic CD4E problem identity but not one universal valve-body or drum cause.
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View P0731 across all makes →Frequently Asked Questions
What does P0731 mean on Mercury?▼
P0731 stands for "Gear 1 Incorrect Ratio." This code means the Transmission/Powertrain Control Module detected an incorrect gear ratio in 1st gear. The module compares input (engine/turbine) speed to output shaft speed; when the car is commanded into 1st but the calculated ratio doesn't match the expected value, P0731 sets. This points to slipping, an incorrect shift, or a hydraulic/mechanical problem rather than just an electrical fault. You may feel slipping, harsh or delayed engagement, or the transmission may go into a limited 'limp' mode. On Mercury specifically, this code is documented across 1 model.
What causes P0731 on Mercury vehicles?▼
Common causes on Mercury: Low or degraded/burnt transmission fluid, Slipping clutch packs or worn friction components, Stuck or faulty shift solenoid affecting 1st gear, Internal hydraulic leak / valve body fault, Worn or failing torque converter. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0731 on a Mercury?▼
Repair costs vary widely depending on the root cause and specific Mercury model.
Which Mercury models have P0731 documented?▼
Au7o has documented P0731 on 1 Mercury model: Cougar.