P0734 on Acura: How to Diagnose & Fix
Gear 4 Incorrect Ratio
3 Acura models · 3 documented issues · 3 critical · $2,500-$6,500 repair
P0734 on Acura by model: symptoms, diagnosis and fix
The ZF 9HP 9-speed automatic introduced on the 2016 MDX suffers from documented hesitation, harsh shifts, lurching, and unexpected downshifts/deceleration. Drivers report the vehicle hesitating from a stop, banging into gear, or briefly losing power. Software miscommunication between TCM, ECM and throttle control is the alleged root cause; a class action was filed alleging Honda knew of the defect from 2015.
Common Symptoms
- Hesitation from a stop
- Hard or banging shifts
- Unexpected downshift while cruising
- Brief loss of power
- Lurching at low speed
How to Fix
Have dealer apply latest TCM/PGM-FI software updates first (covered by powertrain warranty). If symptoms persist, request fluid replacement and dealer escalation; document everything for lemon-law/class-action relief. Avoid jerky throttle inputs while cold.
Sources for this issue (3)
The 1997-1999 3.0CL uses an automatic transmission specific to its V6 model family (the 2.2CL/2.3CL 4-cylinder variants do NOT share this transmission and are not affected). Owners and independent transmission shops widely report failures: slipping under load, not shifting out of 1st until warm, harsh shifts, and eventually total failure. Reports of repeat failures are common. NOTE: this transmission failure pattern is more severe and better documented on the 2nd-gen 3.2CL (2001-2003) than on the 1st-gen 3.0CL; the 1st-gen exhibits the same underlying weakness but at lower failure rates. A critical maintenance detail: this transmission has minimal internal filtration, and the filter is not serviceable without complete teardown. Owners who power-flush a slipping unit dislodge clutch debris and accelerate the failure rather than fix it.
Common Symptoms
- Transmission won't shift out of 1st until engine is warm
- Slipping in higher gears under load
- Rough or delayed engagement from Park to Drive
- Harsh thunk shifts when slowing
- Burnt smell from transmission dipstick
- Repeat failures within 30,000-60,000 miles after replacement
How to Fix
If symptoms appear, immediately switch to ONLY Acura/Honda ATF (never Dextron substitute) and start a regular drain-and-refill schedule at every engine oil change interval (6 months). Do NOT power-flush — this transmission has effectively no serviceable filter and pressurized flushing forces debris through tight passages. If slipping has already started, a transmission specialist (not a quick-lube) needs to drop the pan to check for clutch material in the fluid. Once debris is visible, only a rebuild fixes it ($2,500-3,500). Replacements/rebuilds may need a fresh torque converter — the original is a known weak point. Add an aftermarket transmission cooler at rebuild time; the factory cooling is undersized.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Set of 7 Genuine Honda ATF DW-1, part 08200-9008, for Acura CL / Honda Civic
Repair fluid Honda/Acura automatics requiring ATF-Z1 or DW-1; listing explicitly names Acura CL. Verified repair fluid.
As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.
Owner tips & cautions
- WarningDo NOT power-flush this transmission. It has minimal internal filtration and pressurized flushes dislodge clutch debris into tight passages. Drain-and-refill ONLY.
- TipUse ONLY Acura/Honda ATF, never a 'compatible' Dexron substitute. Wrong fluid accelerates failure on this transmission.
- TipIf you rebuild, add an aftermarket transmission cooler. Factory cooling is undersized and was a contributor to original failures.
Sources for this issue (2)
1999 was the launch year of the 2nd-gen TL with the 3.2L J32A V6 and a new 5-speed automatic. This transmission family turned into one of the worst Acura defects of the early 2000s — torque converter failure, 3rd-gear clutch pack burn-up, blocked oil passages from debris, and complete failure became common. American Honda extended the transmission and torque converter warranties in 2003 (per TSB 02-027). The 1996-1998 TL uses the older 4-speed automatic which is generally reliable; the failure pattern is specifically the 5AT introduced for 1999. If you are car-shopping a 1999 TL, the model year alone does not tell you which transmission you have — the early-1999 carryover may have the older 4AT while the mid-year 2nd-gen launch got the 5AT. Check the build date and trans serial to know.
Common Symptoms
- Flaring on 2nd-to-3rd or 3rd-to-4th upshifts
- Harsh 'thunk' downshifts when slowing
- Slipping in 3rd gear under load
- Transmission shudder at highway cruise
- Burnt-smell or dark transmission fluid
- Check engine light with P0700-series transmission codes
- Complete loss of forward drive (catastrophic stage)
How to Fix
If you own a 1999 TL with the 5AT and it's slipping, flaring on shifts, or showing harsh 1-2 / 2-3 changes: STOP driving aggressively immediately. The damage compounds quickly. Get a transmission specialist (not a dealer) to drop the pan and check for clutch material in the fluid. If found, the only durable fix is a rebuilt transmission ($2,500-4,000) — not a fluid change, not a solenoid swap. The original Honda warranty extension to 7/100k expired in 2006, so out-of-pocket cost is now on the owner. Many owners install an aftermarket transmission cooler with the rebuild — the original spec is undersized for the load and contributed to the failure pattern. Avoid 'flush' services — pressurized flushes on a worn transmission accelerate failure by dislodging clutch debris.
Owner tips & cautions
- WarningDo NOT 'flush' a worn 5AT. Pressurized flushes dislodge clutch debris from the case and accelerate the death of a struggling transmission. Drop and fill with manual fluid changes only.
- TipAlways add an aftermarket transmission cooler with any rebuild. The factory cooler is undersized for this transmission's load and was a contributing factor to the original failure pattern.
- TipWhen shopping a 1999 TL used, check the build date and transmission serial number. Cars built before the mid-year 2nd-gen launch have the older 4-speed and are far more reliable.
Sources for this issue (2)
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 Acura?
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 Acura it is documented across 3 models: MDX, CL, TL.
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 Acura?
Published repair estimates on Acura range from $2,500 to $6,500 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.