How to Test the 1-2 and 2-3 Shift Solenoids (GM 4L60-E)

In this article, I'll show you how to test the transmission shift solenoids (specifically 1-2 solenoid and 2-3 solenoid) on your GM 4.3L, 5.0L, 5.7L pick up, van, SUV.

You'll be surprised just how easy it is to diagnose these shift solenoids when they have failed.

You do have to take some precautions and in this article I'll show you what to do and not do to diagnose a shift solenoid issue with your vehicle.

In case you're wondering how to tell the difference between a bad shift solenoid and internal transmission damage, the following article might be helpful:

  1. How Can I Tell If My 4L60-E Transmission is BAD?.

En Español You can find this tutorial in Spanish here: Cómo Probar los Solenoides de Cambio A y B (GM 4.3L, 5.0L, 5.7L) (at:

Important Suggestions and Tips

Tip 1: Before removing the transmission oil pan, read the section: Before You Remove the Trans. Oil Pan. This section is a must read to avoid any complications you might have in finishing the job.

Tip 2: Shift solenoid A refers to shift solenoid 1-2. shift solenoid B refers to the shift solenoid 2-3.

Tip 3: Removing the shift solenoids should be done with a completely cooled vehicle. Transmission fluid gets hot and remains hot long after the vehicle has been turned off. Be careful, take all necessary safety precautions... your safety is your responsibility.

Tip 4: If your transmission is slipping, replacing the shift solenoids, even if they're fried will not solve the slipping issue.

Shift Solenoid A and B Basics

How to Test the 1-2 and 2-3 Shift Solenoids (GM 4L60-E)

The 4L60-E transmissions uses several solenoids and sensors to control/activate its 4 gears. The two that we're concerned with are the 1-2 and 2-3 shift solenoids.

Depending on the type of scan tool you're using (either a generic scan tool or a professional level technician's scan tool), these two solenoids will be called shift solenoid A and shift solenoid B or 1-2 shift solenoid and 2-3 shift solenoid.

To avoid any confusion with what name is used to identify them:

  1. Shift solenoid A = shift solenoid 1-2. In the photo in the image viewer, this solenoid is identified by the letter A.
  2. Shift solenoid B = shift solenoid 2-3. In the photo in the image viewer, this solenoid is identified by the letter B.

The PCM (Powertrain Control Module = Fuel Injection Computer) activates and deactivates these two solenoids in a predetermined pattern so that 4 specific gear ratios can be achieved. These are:

  1. 1st Gear: Solenoid 1-2: ON     Solenoid 2-3: ON
  2. 2st Gear: Solenoid 1-2: OFF   Solenoid 2-3: ON
  3. 3st Gear: Solenoid 1-2: OFF   Solenoid 2-3: OFF
  4. 4st Gear: Solenoid 1-2: ON     Solenoid 2-3: OFF

When any one of these two shift solenoids fail, the PCM commands the transmission to operate in LIMP IN MODE and this means that the transmission will run in 2nd gear only (no 1st and no 3rd or 4th).

Although there's a lot more to know and learn about the operating theory of the 4L60-E transmission... the above should suffice for our purposes in the article. Let's move on the next subheading and find out what are the most common symptoms when these two buggers fail.

Symptoms of a BAD Shift Solenoid

The most common one is the check engine light will be on with one of the following diagnostic trouble codes:

  1. P0751 1-2 Shift Solenoid Valve Performance (Shift Solenoid A Performance)
  2. P0753 1-2 Shift Solenoid Valve Electrical (Shift Solenoid A Electrical)
  3. P0756 2-3 Shift Solenoid Valve Performance (Shift Solenoid B Performance)
  4. P0758 2-3 Shift Solenoid Valve Electrical (Shift Solenoid B Electrical)
  5. Transmission runs only in 2nd gear. This is known as running in LIMP IN MODE.

The most important thing to remember, when trying to decide if you have a solenoid issue or internal transmission damage (causing the transmission to stay in Limp-In mode) is two very important things:

  1. You'll have a specific transmission solenoid trouble code stored in the PCM's memory.
  2. The transmission doesn't ‘slip’.

OK, with this bit of info under our belts.... let's turn the page and get testing!