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PCM, ECM, TCM, BCM, VATS - GM's Acronyms Explained

Confusing… isn’t it. Getting your head around GM’s acronyms for its control modules and software can be a task in itself, this article aims to explain these terms and where they are used, especially in the world of LS Swaps and LS Conversion Harnesses. Please note, this article is for Australian delivered LS swap vehicles only and may not apply internationally.

Let’s start with the acronyms themselves.

PCM – Powertrain Control Module

A Powertrain Control Module is the brains of the Engine AND Transmission. The “AND” is an important detail, as you will find later. The PCM is found paired with 1999-2005 LS1/LS6 based vehicles. In Australia, there are two main types named P01 and P59, or more commonly referred to as Red/Blue or Green/Blue Variants.

Red/Blue P01 PCM’s are found on the earlier, cable driven variants of the LS1/LS6 and CANNOT be used with a FBW throttle body.

Green/Blue P59 PCM’s are found on the latter, Electronic Throttle VZ 5.7L LS1 Engines. With some rewiring and reprogramming, these computers CAN be changed to work with cable throttles.

These PCM’s also control the transmission of the vehicle, they control certain aspects (Like Reverse lockout solenoid) of the T56 Manual Transmissions and all the functionality of the 4L60e and 4L80e automatic transmissions.

The two variants of PCM look identical from the outside with the only point of visual difference being the keyways on the connectors. The Green connector IS NOT compatible with a RED PCM receptacle and vice versa.

Dirty South Offers Several services for the P01 P59 PCM’s including REPROGRAMMING, NEW CONNECTORS & MOUNTING BRACKETS

ECM – Engine Control Module

An Engine control module is the brains of the Engine and ONLY the Engine. Unlike a PCM, the ECM cannot control the automatic transmissions which they are associated with. GM started to introduce ECM’s in place of PCM’s in the late model, 6L LS2 HSV VZ Commodores. The first of which, was named the E40 controller.

The E40 controller can be identified by its 3 distinct connectors and is only compatible with a very small run of Genuine HSV LS2’s.

Holden E40 ECM

Following this, GM moved to the E38 ECM after a very short run of E40’s. The E38 was used for everything from later LS2’s, L98’s, L77’s to the LS3. The E38 MUST use an electronic throttle body and vehicles which use the E38 cannot directly be used with the earlier PCM’s. The E38 ECM has two connectors known as X1 or J1 and X2 or J2. The X2/J2 connector is often not included if you are purchasing an engine or harness from the wreckers. We stock this connector, and it can be found HERE.

Holden E38 ECM

GM also used another ECM called the E67 which is exclusive to the VF LSA Engine in Aus vehicles. This controller has three connectors as seen below.

Holden E67 ECM

As stated above, these controllers do not directly control the transmission. Which brings us to our next acronym.

TCM – Transmission Control Module

The Transmission Control Module is the brains of the Automatic Transmission and ONLY the transmission. With the earlier Gen 3 PCM’s the Transmission controller was integrated with the engine controller, however with the move to ECM’s a separate controller was needed.

For the small run of 4L60e transmissions that were mated to Gen 4 engines with e38 ECM’s a standalone TCM was used called the T42. With the introduction of the 6L80e range of transmissions, the TCM was added to the mechatronics of the transmission itself and is located within the valve body. The ECM communicates to the TCM via a computer language called CAN (Controller Area Network) transferring vital data like throttle position and RPM where the TCM then controls the solenoids inside the transmission.

BCM – Body Control Module

The Body Control Module acts as a controller for various other functions of the donor vehicle, it controls several circuits from vehicle security to interior lights. The name BCM refers to several different models of Body Control Module used over many years of LS vehicles. Generally, in conversions the BCM is deleted as it adds unnecessary complexity to the harness.

When a body control module is removed from the control electrics package, reprogramming is required, and the security software or VATS needs to be removed.

VATS – Vehicle Anti Theft Software

VATS - Vehicle Anti Theft Software is a feature in all Gen 3 and 4 ECM’s that will cut the engine if a signal from the original key is not received. Unlike earlier PCM’s, the VATS cannot be bypassed easily and to avoid turning it off in the software the original BCM, Key Reader and Key must be used, which adds unnecessary complexity.

VATS removal can be done easily and simply to most ECM and PCM’s on the bench. We offer this service for P01, P59 and E38 ECM’s HERE.

We hope this clears up some of the confusion around the acronyms and assists you in your LS Swap.





  • Hello just after advice and if you sell anything that can help me I have a 2003 Holden wk caprice I bought it as a roller no engine or engine loom and ecu I have a ls2 loom with a e40 ecu and a l77 crate engine was wondering what’s needed to put that engine in my car and get it running I will be using the ls1 auto thank you kind regards Anthony

  • Hi there. I’m swapping an LS1 with 4l69e into a Holden Rodeo. With stand alone loom what other parts pcm ect will I require. I have them all. I was thinking of running standalone unit on the trans.

    Timothy Cubelich

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