Cadillac CTS
Transmission Problems

CTS Transmissions by Generation

The RPO code on the service parts label is the only reliable way to order parts on a CTS. The third-generation car in particular changed transmissions partway through its run, and engine size alone does not tell you which unit you have.

First Generation: 5L40E (2003-2007)

Limp mode and random solenoid codes from the case connector

The 5L40E has a well-known habit: the seal on the case pass-through connector hardens, and transmission fluid wicks out through the connector and up the wiring harness toward the control module. The result is intermittent limp mode, harsh shifts and solenoid circuit codes for several unrelated circuits at once. Shops replace solenoids and the problem comes back, because the fluid is still wicking.

Unplug the connector at the case and look inside the harness side. If it is wet with ATF, you found it. The fix is a new connector seal and cleaning or repairing the harness, and on bad cases the harness itself. Our 5L40E problems guide covers it in detail.

Harsh or flared shifts

With the connector ruled out, harsh engagements and flare on a specific shift point to the pressure control solenoid, a shift solenoid or valve body wear. Our 5L40E solenoid kit replaces the set, and a 5L40E/5L50E filter and pan gasket kit goes in with any service.

Second Generation: 6L50 (2008-2014)

3-5-reverse wave plate

The signature failure for the whole 6L family. The wave plate in the 3-5-reverse clutch cracks and breaks apart, and you lose third, fifth and reverse. The car may still move in first, second, fourth and sixth, which tempts owners to keep driving it while the debris works through the rest of the transmission. Do not. The fix is a teardown with the updated wave plate and new 3-5-R clutches, plus a thorough cleanout. See our 6L50 problems guide and 6L family wave plate guide.

Torque converter shudder

A shudder at 40 to 60 mph under light throttle on a CTS is almost always the converter clutch, and on the 6L50 it is usually fluid related. A full exchange with fresh Dexron VI often fixes a mild case. Left alone, the converter wears and contaminates the transmission.

Valve body and solenoid wear

Harsh shifts, flares or delayed engagement point to valve body bore wear or a tired solenoid, the same bores that wear in the 6L80. Our 6L50 solenoid kit handles the solenoid side, and the 6L50 overhaul kit covers gaskets and seals when the unit comes apart.

Third Generation: 8L45 (2016-2019)

The 8L45 brought eight speeds and a new set of complaints, mostly harsh or clunky low-speed shifts and shudder. Much of it is software and fluid. GM released calibration updates for shift quality on its eight-speeds and changed the recommended fluid on many of them to address shudder, so check for both before condemning hardware. When the valve body itself is the problem, we carry an 8L45 valve body. Our 8L45 problems guide has the details.

Fluid and Service

The 5L40E and 6L50 use Dexron VI. Eight-speed cars should use the exact fluid in the current GM service information for that transmission, because it has changed. None of these are truly lifetime fluids. On a CTS, plan on a change every 45,000 to 50,000 miles. We carry ACDelco Dexron VI by the gallon.

The six- and eight-speed cars have no dipstick. The level is checked at a check plug with the fluid at temperature, read on a scan tool. Do not fill these by guessing.

Codes You Will Most Likely See

• Gear ratio codes (P0731-P0736) or P0752. A clutch is slipping. Paired with missing third, fifth and reverse on a 6L50, it is the wave plate.
• Several solenoid circuit codes at once on a 5L40E. Check the case connector for fluid before replacing a single solenoid.
• P0741 or P2763-family converter codes. Converter clutch slip or control. Start with the fluid.
• Fluid temperature or internal control module codes. On the six- and eight-speeds the control module and temperature sensor live with the valve body, so these often mean pan-down work.

Save the codes and freeze frame data before clearing anything. Clearing also wipes the learned shift values, and the car will shift oddly for a while afterward, which muddies the diagnosis.

Buying a Used CTS

On a first-gen car, look at the transmission connector for fluid and ask about intermittent limp mode. On a 2008-2014, make sure it has third, fifth and reverse after a long warm drive, and feel for shudder at steady highway speed. On any CTS, scan for codes and ask for fluid service records. Cadillac buyers often assume the dealer handled it; usually nobody did.

Repair Costs

Bottom line: a first-gen CTS with random limp mode is a wet connector until proven otherwise. A 2008-2014 that loses third, fifth and reverse is a wave plate.

FAQ

What transmission is in my Cadillac CTS?

2003-2007 automatics use the 5L40E, 2008-2014 use the 6L50, and the 2014-2019 car started with a six-speed and moved to the 8L45 eight-speed for 2016. CTS-V models used the T56, 6L90, TR6060 or 8L90. Check the RPO code.

Why does my 2003-2007 CTS go into limp mode randomly?

Very often transmission fluid wicking through the 5L40E case connector into the wiring harness. Check the connector for ATF before replacing solenoids.

Why did my CTS lose reverse, third and fifth?

On a 2008-2014 with the 6L50, the 3-5-reverse wave plate has likely broken. It needs a teardown with the updated part.

Does the Cadillac CTS have a transmission dipstick?

The six- and eight-speed cars do not. The level is checked at a check plug with the fluid at temperature read on a scan tool.