How Can I Tell If My Automatic Transmission Needs An Overhaul?

This tutorial is a primer that'll help you identify the problem (with your vehicle's automatic transmission) as either being electrical in nature or as being some sort of internal damage that'll require an overhaul.

Now, although in this article I won't be showing you how to tear down your transmission, it will help you to find out if your electronically controlled 4T60-E (or 4T65-E) transmission issue, in your 3.1L, 3.4L, or 3.8L V6 GM vehicle, is due to a malfunctioning shift solenoid/sensor or internal damage.

You can find this tutorial in Spanish here: Cómo Saber Si la Transmisión Ya Falló (3.8L GM 4T60-E/4T65-E) (at: autotecnico-online.com).

Basics Of The 4T60-E (4T65-E) Automatic Transmission In Your GM Vehicle

Depending on the year of your GM vehicle, it'll either use the 4T60-E or the 4T65-E automatic transmission (technically, it's called a transaxle). These two are not interchangeable.

Here are some more specifics:

4T60-E

• Introduced in 1991 and used in almost all of GM's front wheel drive (FWD) vehicles up until the late 1990's. The 4T60-E's upshifts and downshifts are computer controlled by way of two shift solenoids, as such, it doesn't have a kickdown cable.
• There are several different versions of the 4T60-E and most of their internal electronics are NOT compatible with each other. Not to mention that the Final Drive Ratio will not be the same.
• If replacing the complete transaxle, you should only replace with a unit that's verified to be the same. Using the wrong 4T60-E unit will cause you a head-ache, since the transmission will not function correctly, if at all.

4T65-E

• Introduced in 1997 and eventually replaced the 4T60-E. This automatic transaxle was used up until 2011.
• Not interchangeable with the 4T60-E.

NOTE: The following link will help you in identifying the 4T60-E or 4T65-E transmission in your vehicle: GM FWD Transmission ID Charts (at: www.gmtuners.com)

Let's now take a look at the most common types of failure in the next heading.

Two Of The Most Common Transmission Failures

The most important thing to know, when trying to troubleshoot a transmission problem, is that the 4T60-E (and 4T65-E) automatic transmission usually fails in one of two ways:

1. Transmission is ‘slipping’.
   • A transmission that's ‘slipping’ indicates internal mechanical failure.
   • A low level of transmission fluid (usually due to a transmission fluid leak) can also cause the transmission to ‘slip’.
   • In case you're wondering: ‘slipping‘ can be best described as having the transmission go into neutral, although it's in drive, and not move the vehicle no matter how much you step on the accelerator.
2. Transmission does not shift out of 2nd gear.
   • This generally happens when the PCM senses an electrical problem and commands the transmission to stay in what is known as ‘Limp In Mode’.
   • In ‘Limp In Mode’, the automatic transmission will not downshift or upshift at all.
   • The usual cause of this condition is an electrical issue, like a bad shift solenoid. Although some internal mechanical problem/damage can also cause this.

Each one of the above conditions has a specific cause and in the next sections, we'll explore this a bit more in-depth.

How Can I Tell If It's Just A Solenoid Failure?

The electronically controlled 4T60-E/4T65-E has several solenoids and sensors that the PCM needs to control the upshifts and downshifts. If any one of these sensors/solenoids fail or the fuse(s) that supplies the solenoids gets blown, the transmission will go into ‘Limp In Mode’.

What makes it pretty easy to tell if the automatic transmission failure is just a solenoid related issue is the fact that the transmission doesn't ‘slip’.

Here are some very specific symptoms you'll see when a transmission solenoid goes bad:

1. The PCM is also gonna' light up the check engine light (CEL) and store a specific shift solenoid diagnostic trouble code (DTC). All transmission diagnostic troubles codes start with: P07XX (the XX being the last 2 digits of the DTC).
2. You'll see one or several of the following transmission diagnostic trouble codes:
   • P0700: Transmission Control System Malfunction.
   • P0751: Shift Solenoid A Malfunction.
   • P0755: Shift Solenoid B Malfunction.
   The above are just some of the transmission diagnostic trouble codes you'll see since there are quite a few that I didn't have space to list.
3. The speedometer does not work and you might have one of the following trouble codes:
   • P0500: Vehicle Speed Sensor Malfunction.
   • P0501: Vehicle Speed Sensor Range/Performance.
   • P0502: Vehicle Speed Sensor Low Input.
   • P0503: Vehicle Speed Sensor Intermittent/Erratic/High.
4. Your 4T60-E/4T65-E automatic transmission will stay in only one gear no matter what the vehicle speed.
5. As you accelerate your vehicle, it feels very underpowered. This is due to the fact that the transmission is starting out in 2nd gear.
6. At speeds over 35 MPH, the engine feels like it's over-revving. This is also due to the fact that the transmission is staying in 2nd gear and the gear ratio provided by 2nd gear is gonna' keep the engine working pretty hard at any speed above 35 MPH.

Remember, what will tell you that you have a solenoid or internal transmission sensor problem is:

1. You'll have a specific transmission diagnostic trouble code (or a speed sensor diagnostic trouble code).
2. The automatic transmission does not ‘slip’, no matter how many times you road test your vehicle.
3. The 4T60-E stays/4T65-E in ‘Limp In Mode’ (note: see Transmission With Both Solenoid Failure And Internal Damage).

Let's turn the page and find out more about the specific symptoms a 4T60-E/4T65-E with internal damage.