P0734 on Mercury
Gear 4 Incorrect Ratio
P0734 on Mercury vehicles indicates gear 4 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 4th gear. The module continuously compares input shaft speed to output shaft speed; if the ratio in 4th gear doesn't match the expected value, it sets P0734. This usually indicates the transmission is slipping or not fully engaging 4th gear due to a hydraulic, friction, or solenoid problem. Symptoms include slipping, flaring RPM, harsh or missed shifts, and possibly limp mode.
Common Causes of P0734
- •Low or degraded/burnt transmission fluid
- •Slipping clutch packs or worn friction elements in 4th gear
- •Stuck or faulty shift solenoid
- •Valve body / internal hydraulic leak or restriction
- •Worn or failing torque converter
- •Faulty input or output speed sensor
- •Internal mechanical wear (bands, planetary gears)
P0734 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 P0734 across all makes →Frequently Asked Questions
What does P0734 mean on Mercury?▼
P0734 stands for "Gear 4 Incorrect Ratio." This code means the Transmission/Powertrain Control Module detected an incorrect gear ratio in 4th gear. The module continuously compares input shaft speed to output shaft speed; if the ratio in 4th gear doesn't match the expected value, it sets P0734. This usually indicates the transmission is slipping or not fully engaging 4th gear due to a hydraulic, friction, or solenoid problem. Symptoms include slipping, flaring RPM, harsh or missed shifts, and possibly limp mode. On Mercury specifically, this code is documented across 1 model.
What causes P0734 on Mercury vehicles?▼
Common causes on Mercury: Low or degraded/burnt transmission fluid, Slipping clutch packs or worn friction elements in 4th gear, Stuck or faulty shift solenoid, Valve body / internal hydraulic leak or restriction, 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 P0734 on a Mercury?▼
Repair costs vary widely depending on the root cause and specific Mercury model.
Which Mercury models have P0734 documented?▼
Au7o has documented P0734 on 1 Mercury model: Cougar.