Lexus IS250 / IS350
Transmission Problems

When Lexus redesigned the IS for 2006, it put the 2.5L IS250 and the 3.5L IS350 on a rear-drive platform and backed both with the A960E, Aisin's six-speed automatic for longitudinal V6 engines. The same transmission went into the GS300 and GS350. The IS250 was also offered with a six-speed manual for most of the run, and the IS250 AWD used a different six-speed from the A760 family with a transfer case bolted to it.

The A960E is a strong transmission, and plenty of IS350s with 200,000 miles still shift fine. But these cars are now 12 to 20 years old, many have never had a fluid change, and a fair number have been driven the way a sport sedan begs to be driven. The failures are predictable, and most of them are cheaper than a dealer quote suggests.

IS Drivetrain at a Glance

The IS F used an eight-speed, and the 2014-and-later rear-drive IS350 moved to an eight-speed as well; those are different transmissions. Fluid for the A960E is Toyota WS. For the transmission itself in depth, see A960E problems and cost.

What Actually Fails

1. Converter shudder at 35-55 mph

The most common IS complaint by a wide margin: a fine vibration at light throttle, like driving over coarse pavement, that goes away the moment you press harder or lift off. That is the converter clutch slipping as it applies. On a car with original fluid, a proper WS drain and fill often fixes it or improves it a lot. If it is back within a few thousand miles, the converter lining is worn and the converter needs replacing.

2. Harsh 1-2 or 2-3 shifts

A bang into second, worse when cold, or a 2-3 that feels like someone tapped your rear bumper. Hardened accumulator seals, worn valve body bores and a linear solenoid that no longer modulates pressure smoothly are the usual causes. Always start with fresh fluid on a car that has never been serviced. If clean, recent fluid does not change anything, it is the solenoids or the valve body.

3. Linear solenoid codes and erratic shifting

The A960E controls line pressure and clutch apply with linear solenoids (the SL and SLT circuits) mounted on the valve body. When one drifts or fails electrically you get solenoid performance codes, harsh or late shifts, and sometimes a limp mode stuck in a fixed gear. They come out with a pan drop and the car stays on the ground. We carry the A960E 9-piece solenoid kit and, for worn bores, the complete A960E valve body with solenoids.

4. Slipping and burned fluid

Once the clutches are worn, the engine flares between gears or under load and the fluid smells burned. That is a rebuild. IS350s that have seen a lot of hard launches tend to get here first.

5. Things that are not the transmission

Clunks on takeoff from worn rear differential mounts and a clunk from the driveshaft are common on these cars and get blamed on the transmission. So does a rough idle in gear from carbon buildup on the IS250's direct-injection engine. Check those before anyone pulls the pan.

Diagnose Before You Buy Parts

• Read codes and live data. Solenoid codes with clean fluid point at the valve body.
• Check the fluid level hot at the overflow plug. There is no dipstick, and a low unit shifts badly.
• Note when it happens. Steady-speed vibration is the converter. A bang on a specific shift is pressure control. Rpm flare is clutches.
• On AWD cars, confirm which transmission you have before ordering anything; A960E parts do not fit.

WS Fluid Service Done Right

Lexus calls the fluid lifetime. It is not. The A960E is filled and checked through an overflow tube at a set fluid temperature with the engine idling, so a quick-lube top-off by guesswork usually leaves it wrong. Each drain and fill replaces only part of the fluid, so on a neglected car plan on two or three, a few hundred miles apart. Use genuine Toyota WS fluid or Idemitsu TLS-LV WS; do not use a universal fluid.

Real Repair Costs

Rebuild or Used?

Rear-drive A960E donors are less common than the front-drive Lexus and Toyota units, and many come from cars with unknown histories. On an IS350 you plan to keep, a rebuild with a new converter and updated solenoids is usually the better value. If the clutches are fine and the problem is shift quality, the valve body or solenoid route fixes it for a fraction of the cost. AWD IS250 owners need parts for their own transmission, not A960E parts; the A760E rebuild kit for the IS250 is the starting point there.

FAQ

What transmission is in a Lexus IS350?

The 2006-2013 rear-drive IS350 uses the Aisin A960E six-speed automatic. The 2014-and-later rear-drive IS350 uses an eight-speed.

Why does my IS250 shudder at highway speeds?

A vibration at light throttle between about 35 and 55 mph is the torque converter clutch slipping on apply. Try a correct WS fluid service first. If it comes back quickly, the converter is worn.

Why does my Lexus IS shift hard from 1st to 2nd?

Hardened accumulator seals, valve body wear or a drifting linear solenoid. Start with fresh WS fluid on a car that has not been serviced, then look at the solenoids and valve body.

Can I replace the A960E solenoids without removing the transmission?

Yes. The solenoids are on the valve body and are reached by dropping the pan, so the transmission stays in the car.

How much does an IS350 transmission rebuild cost?

An independent shop rebuild of the A960E usually costs $3,200 to $5,000. A used unit installed typically runs $2,000 to $3,500.