P0734 on Cadillac: How to Diagnose & Fix
Gear 4 Incorrect Ratio
1 Cadillac model · 1 documented issue · 1 critical · $600-$4,000 repair
P0734 on Cadillac by model: symptoms, diagnosis and fix
The 4T80-E four-speed used behind the Northstar develops two documented and related faults. The lower control valve body and its channel plate/gasket leak internal pressure, producing 1-2 shift delays, slips and flares with P0731 or P0732, and slipping or complete loss of fourth gear with P0734. Where the pressure loss has been present for a while, the fourth-gear (overdrive) clutch pack cooks off its friction material - owners report finding the pan full of clutch debris and the fourth clutch stripped bare. The transmission fluid pressure switch assembly sets similar codes and is a cheaper first suspect. Owners also report the plastic locating ears on the valve body breaking. Fluid contaminated with clutch material is what carries the failure across the rest of the clutch packs, which is why a late fluid change on a slipping unit often makes it worse rather than better.
Common Symptoms
- Slipping or no fourth gear / overdrive
- Delayed, slipping or flaring 1-2 shift
- Harsh or jolting shifts
- Check engine light with transmission codes
- Clutch material in the transmission pan
How to Fix
Scan the transmission and inspect the fluid and pan first. A clean-fluid pressure-switch or lower-valve-body fault may be serviced in-car; friction material or a lost fourth gear requires a rebuild or replacement unit.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Transtar/TransTec 4T80-E valve-body cover, spacer and channel-plate gasket set$18
1996-2005 Cadillac DeVille/Concours 4.6L 4T80-E branch. Gaskets only: the pressure-switch assembly, valve body and any fourth-clutch rebuild parts are separate and must be identified from the codes and transmission build.
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Sources for this issue (3)
P0734 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0734 mean on a Cadillac?
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 Cadillac it is documented across 1 model: DeVille.
What are the most common causes of P0734?
The most common causes of P0734 are: 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). The specific cause varies by vehicle.
How much does it cost to fix P0734 on a Cadillac?
Published repair estimates on Cadillac range from $600 to $4,000 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0734 on a different make?
View P0734 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.