Skip the auto shop - Our mechanics make house calls

Q: What Do Transmission Error Codes Tell You?

asked by on

What do transmission error codes tell you?

Using transmission error codes is a necessary procedure for a transmission technician since automatic transmissions have been computer controlled for over 20 years. The transmissions currently in use are very different to diagnose and repair than transmissions from decades ago. For correct operation, transmissions rely on accurate electrical inputs from multiple sensors. A transmission control module (TCM) processes the inputs, “decides” what the correct action is for the current conditions, and sends out commands to actuators. The required training, electrical understanding, tooling, and diagnostic skills required of transmission technicians have all increased dramatically. Fortunately, the automatic transmission control systems are designed to be able to provide some clues to a technician about what “might” be faulty. These are the fault codes or error codes. A technician obtains them from the vehicle’s control module using a scan tool. Codes may indicate issues with the speed sensors, shift solenoids, pump pressures, valve body circuits, or slipping clutches. The fault can be the TCM itself, programming calibration, or electrical wiring, connections, or grounds for any of these. The scan tool and code doesn’t tell a technician what part to replace, but does provide direction to an experienced, trained technician in the diagnostic process.

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: I felt a jolt while driving - could it be a transmission issue?

Hi. This is a good indication that the transmission has overheated and damaged a lot of the internal parts of the transmission. This could have been caused by low transmission fluid or extremely dirty transmission fluid causing a cloth in...

Q: I accidentally drove through 2 feet of water, I have replaced several parts but the car still runs poorly

You did not mention replacing the air filter after it got wet. The engine and its sensors were not designed to go through water and will get damaged. You may have also damaged internal engine parts like bending engine piston...

Q: Car not running after throttle body with IAC valve replacement

Hi, thanks for writing in. I would recommend retracing your steps. You are definitely on the right track. It sounds like you did a good amount of work to your car, and it is likely that something may been skipped...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
How Long Does a Distributor O Ring Last?
The distributor is part of the ignition system in your vehicle and its purpose is to route high voltage from the ignition coil to the spark plug. The spark plug then...
How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...