6F35 TRANSMISSION - FLUID LEAK AT LEFT SIDE HALFSHAFT SEAL BUILT ON OR BEFORE 10/14/2013 ISSUE Some 2009-2014 Escape, 2009-2011 Mariner, 2010-2014 Fusion, 2010-2011 Milan, 2012-2014 Edge/Explorer, and 2013-2014 Taurus/MKT/MKZ vehicles built on or before 10/14/2013 and equipped with a 6F35 automatic transmission may exhibit a fluid leak from the left hand (LH) transmission halfshaft seal due to wear on the transmission case bushing.
full bulletin at NHTSA ↗2009 Mercury Mariner powertrain problems
moderate 39 complaints filed with NHTSA · avg repair $2,500 · see powertrain across all vehicles →
Failure mileage
Complaints
39
Recalls
0
Avg fix
$2,500
When does it fail?
Of the 39 powertrain complaints filed for the 2009 Mercury Mariner, here's the actual mileage breakdown — failures cluster heaviest at 75,000-100,000 mi.
0-25k
25-50k
50-75k
75-100k
100-125k
125-150k
150k+
Each bar shows the share of total complaints filed at that mileage range. Peak failure window highlighted. Some owners report problems earlier; some make it well past 150,000 miles symptom-free. Maintenance habits and driving conditions shift the curve as much as mileage alone.
What stands out
Owners have filed 39 powertrain complaints with NHTSA against this vehicle, but no formal recall covers the issue — the federal record reflects what manufacturers have admitted, not everything owners are reporting.
Among the 7 model years of Mercury Mariner in our records for powertrain problems, this one ranks #3 by owner-complaint volume.
Is there a fix? Manufacturer service bulletins
The manufacturer has issued service bulletins covering powertrain on this vehicle — documented repair instructions, service campaigns, or warranty extensions sent to dealers. A TSB isn't a recall (it's not a free safety remedy), but it's the manufacturer acknowledging the issue and how to fix it.
6F35 Transmission - Fluid leak at left side halfshaft seal - built on or before 10/14/2013
full bulletin at NHTSA ↗Source: NHTSA manufacturer communications. Bring the bulletin number to your dealer or shop.
The failure pattern owners describe
Owners report two dominant failure types affecting the 2009 Mercury Mariner's powertrain. The most common is sudden loss of acceleration with wrench-light illumination: engine revs but the vehicle crawls at 1–15 mph, leaving drivers stranded in traffic. This happens at any speed and resolves after shutdown and restart—but recurs unpredictably, sometimes within minutes, days, or weeks. One dealership service tech claims he handles roughly three such cases per week from throttle-body failure alone. Dealers recommend throttle-body replacement (~$120), yet owners report the problem returning even after that repair.
The second major issue involves the 6F35 automatic transmission: fluid leaks from the left-side halfshaft seal, and the transmission slips (RPM climbs without speed gain). One owner documented a transmission flushed, replaced, and cooler-line repaired in 2010, then a valve-body replacement in 2013, followed by a full rebuild with melted plastic debris—all within three years of ownership, totaling $2,500-plus. A mechanic noted an available service kit for the seal issue but owners received no notification, forcing costlier repairs.
Additional complaints cite transmission hard-shifts, jerking, and rare but serious unwanted acceleration surges. Dealers and independent mechanics frequently cannot replicate faults or find diagnostic codes, leaving owners stranded and uncertain. Ford states it has no knowledge of these problems on other vehicles and offers no recall coverage.
Same Mercury Mariner powertrain reports on nearby years: 2006 · 2007 · 2008 · 2010 · 2011
Failure modes owners describe
Throttle body malfunction / loss of acceleration
Engine loses power and refuses to accelerate; wrench light (powertrain fault indicator) illuminates. Vehicle enters limp-home mode or near-idle condition. Problem resolves after shutdown and restart, often temporarily. Some owners report the issue repeating multiple times over weeks or months despite throttle body replacement.
When: Occurs at any speed (25–75 mph noted); can happen during highway merges, city driving, or at stop lights. Often during cold starts or when driver demands acceleration.
Symptoms owners cite: Sudden loss of acceleration response despite pressing pedal; Wrench light illumination on dashboard; Engine revs but vehicle barely moves (1–15 mph only); Rough idle or near stall; Vehicle jerks or shakes when attempting to accelerate; Limp-home mode activation (forced low-speed operation)
Codes mentioned: P2112 (Throttle Control Actuator System Stuck Closed), P2111 (Throttle Actuator Stuck Open), Wrench light (generic powertrain fault)
Repairs/costs cited: Dealers recommend throttle body replacement (cost ~$120–reported). One owner had throttle body replaced but problem recurred. Mechanic cleaned throttle actuator with temporary success (~1 month) before issue returned. Service tech at one dealership reports handling ~3 cases per week at that location alone.
Recalls/TSBs owners mention: No recall found by owners searching. One dealer stated throttle body failure at 39,000 miles should not occur but offered no warranty coverage. TSB mentioned (NHTSA Item 10039137) for transmission but not specifically for throttle body. Dealer at one location suggested filing complaint to Ford customer service is a waste of time.
6F35 automatic transmission slipping and fluid leak
Transmission slips (RPM rises but vehicle speed does not increase) and leaks transmission fluid from the left-side halfshaft seal. Internal wear damage occurs due to low fluid level. Some owners report the problem persists for years after purchase despite dealer visits. Repair escalation from seal kit service (~$500–few hundred dollars) to full transmission rebuild/replacement ($2,500+) documented.
When: 2–3 years of ownership reported; 39,000–76,000 miles noted. Leakage worse during cold starts or cold weather. Slipping occurs during acceleration, gear changes, or hill climbing.
Symptoms owners cite: Transmission slipping (tachometer rises but no speed increase); Hard or sluggish acceleration; Transmission fluid leaking underneath vehicle; Surging and bucking during gear transitions; Jerking when accelerating; Vehicle hesitates to select gear from stop
Codes mentioned: 6F35 (transmission model identifier), Fluid leak—seal, left side halfshaft
Repairs/costs cited: One owner documented service history: transmission flushed/replaced (01/10), cooler line replacement (08/10), valve body replacement (01/30/13), then transmission rebuild with melted plastic debris removed (03/21–23/13). Extended warranty company initially refused full replacement, approved rebuild only. Subsequent starter failure discovered post-rebuild. Mechanic noted repair failures recurring soon after 2010 work. Service kit reportedly available for seal issue but owners not notified, leading to costlier repairs.
Recalls/TSBs owners mention: Technical Service Bulletin available (NHTSA Item 10039137: Powertrain: Automatic Transmission) but no recall issued. No further assistance offered per one complaint. Recall notice later received by another owner for transmission solenoid regulator valve.
Transmission overdrive piston failure / high-gear slipping
Transmission slips in 5th and 6th gear with excessive vibration, high RPM, and minimal acceleration response despite pedal input. Failure attributed to overdrive piston malfunction. Problem recurred twice after dealer repair. Vehicle also rolled while parked on incline (safety hazard).
When: 13,088 miles at failure; recurred after service repair.
Symptoms owners cite: Excessive vibration; Engine over-revving (high RPM); Transmission slipping in upper gears (5th–6th); Minimal acceleration response; Vehicle rolling on incline while parked
Codes mentioned: Overdrive piston failure (diagnosed by dealer)
Repairs/costs cited: Dealer confirmed overdrive piston as failure cause and repaired. Issue recurred identically twice after repair. Vehicle exhibits unsafe behavior (rolling on incline).
Hard/harsh transmission shifts and jerking
Transmission shifts are abrupt and jerky; vehicle accelerates or decelerates with harsh engagement. Inconsistent shift performance noted. Problem may persist even after powertrain control module reprogramming or valve body replacement.
When: 23,000–78,000 miles. Occurs during low-speed acceleration (10–40 mph), stop-light starts, and gear changes.
Symptoms owners cite: Hard upshifts and downshifts; Jerking acceleration; Vehicle shaking or vibrating during gear engagement; Sluggish or inconsistent acceleration response; Stalling at stop light (transmission fails to downshift)
Codes mentioned: Press regulator valve sticking (6F35 transmission)
Repairs/costs cited: Powertrain control module reprogramming performed but inconsistency persisted. Valve body replacement completed but did not resolve all issues. Problem not consistently replicable by dealer, limiting diagnostic certainty.
Recalls/TSBs owners mention: Powertrain control module reprogramming offered as initial fix. Prior recall (September 2010) included PCM reprogramming and PLM replacement on one vehicle. No further remedy provided for persistent cases.
Unwanted vehicle acceleration / speed surge
Vehicle suddenly accelerates to unintended high speed without driver input or due to minor throttle application. Occurs while on cruise control or during normal driving. Represents serious safety hazard.
When: On highway at 75 mph (cruise control engaged); during turns. One prior occurrence noted before current incident.
Symptoms owners cite: Sudden rapid acceleration to 95 mph from 75 mph cruise; Engine revving up without pedal input; Speed surge during turning; Jerking forward at stop light
Repairs/costs cited: All repairs performed by Ford dealership. Problem recurs despite prior service.
Recalls/TSBs owners mention: Dealership diagnosed as transmission problem; repairs completed but issue persists.
Vehicle stalling during operation
Engine suddenly cuts off while driving at various speeds. Vehicle may stall multiple times within short trips. Restarts normally after shutdown. Wrench light may or may not illuminate. Dealers and independent mechanics unable to replicate or diagnose problem despite diagnostic scans.
When: At stop lights, in traffic, during turns, on expressways. Can occur multiple times in a single trip or days apart.
Symptoms owners cite: Engine cut-off while idling or driving; Loss of all power steering and braking assist; Rough idle before stall; Stalling at stop lights or during acceleration from stops; Wrench light may illuminate
Codes mentioned: P2111 (Throttle Actuator Stuck Open), No codes detected in some cases
Repairs/costs cited: Mechanic cleaning of throttle actuator provided temporary relief (~1 month before recurrence). Diagnostics often yield no fault codes. Multiple mechanics and dealerships unable to pinpoint cause. Problem unresolved in most cases.
Recalls/TSBs owners mention: Ford Motor Co. stated no knowledge of problem; suggests issue does not exist on other vehicles.
Transmission drive-chain noise and shifting irregularity
Rear-end squealing noise upon acceleration; transmission does not perform properly during normal driving (hesitation to upshift, delayed response). Drive chain was disassembled and replaced by dealership, but noise persisted and grew louder. Ford Engineering stated noise should not be a problem.
When: Early ownership (complaint filed ~2009–2010). 12/9–12/16/2009 in shop.
Symptoms owners cite: Squealing noise from rear of vehicle during acceleration; Hesitation to upshift or unresponsive transmission during merging; Vehicle accelerating or not accelerating when inappropriate
Repairs/costs cited: Drive chain disassembled and replaced. Noise persisted and worsened over time. Ford Engineering deemed noise acceptable.
Recalls/TSBs owners mention: Recall notice received for transmission solenoid regulator valve. Prior service (PCM reprogramming, PLM replacement) performed under earlier recall.
Synthesized from 39 NHTSA owner complaints — unverified consumer allegations, summarized for patterns. The verbatim filings appear below.
What owners are reporting 4 most recent
I was driving my 2009 mercury mariner and suddenly lost the ability to accelerate. A wrench light illuminated on my dash and the only thing I could do was coast to a stop. Pushing the gas pedal did nothing. I was able to very slowly get the car to a parking lot (it moved at an idle speed, but would not accelerate otherwise). When I got to the parking lot, I turned the car off. After waiting…
Tl* the contact owns a 2009 mercury mariner. The contact stated that while driving 65 MPH, there was a noise heard from the engine. The vehicle was taken to a mechanic who inspected the vehicle and discovered that there was no transmission fluid in the required reservoir. The mechanic informed the contact that the seal from the transmission was leaking fuel and referred her to a transmission…
Driving my 2009 mariner premier about 35/45 MPH when wrench symbol comes on indicating throttle control powertrain / transmission problem car is not accelerating properly and transmission is jerking when I step on the gas pedal and the car shakes vibrates and feels under powered. Got home and parked it. Started it up and now check engine light is also on. Is this covered by the recall for…
While driving down the road anywhere from 20-55 MPH, the car seems to stall out and the accelerator no longer works. You have to pull over and shut the vehicle off and it will start again. Sometimes the same problem will occur again within seconds, minutes, or days later.
Had powertrain trouble with your 2009 Mercury Mariner?
File a complaint with NHTSA → It's free, official, and how every report above got here — owner filings are the federal safety record this page is built on.
Common questions
How serious is the powertrain problem on the 2009 Mercury Mariner?
It's a documented issue but not catastrophic. 39 complaints have been filed. Repairs average $2,500 and most owners catch it before it causes a breakdown.
At what mileage does the powertrain typically fail?
Across the 37 complaints that reported odometer mileage, most powertrain failures cluster between 51,410 and 95,000 miles, with the median around 69,000. A quarter of owners report trouble before 51,410; a quarter make it past 95,000. Maintenance history matters more than the odometer alone — this is the reported failure window, not a guarantee.
What does it cost to fix?
Independent shops typically charge around $2,500 for powertrain repairs on this vehicle. Dealer pricing tends to run 20-40% higher. The exact figure depends on the specific failure mode, parts availability, and your local labor rates. If you're outside factory warranty, an extended service contract often covers this category.
Are there any recalls related to powertrain?
No active recalls currently cover powertrain issues on this vehicle. The complaints filed represent owner-reported failures that haven't risen to the level of a manufacturer-issued recall — but they're still worth knowing about before you buy or budget for repairs.
Related
Complaint and recall data sourced from the National Highway Traffic Safety Administration (NHTSA)
public records database. Verify the raw federal record at
nhtsa.gov/vehicle/2009/Mercury/Mariner.
Severity ratings are derived from reported crashes, fires, injuries, and fatalities. Repair cost estimates are
independent-shop national averages and may differ in your area. Some links on this page are affiliate links.