AAMCO San Marcos, TX

1206 Highway 123, San Marcos, TX 78666

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External Diagnostic Service

The AAMCO External Diagnostic Service is the best transmission checkup available anywhere. Our Centers’ certified technicians can get to the bottom of any transmission problem. With today’s more complex, computer-controlled transmissions, it takes a real expert to be able to diagnose a transmission problem correctly. Getting that diagnosis right can save you a lot of money. The AAMCO External Diagnostic Service is a systematic and comprehensive external evaluation of the overall performance and condition of your transmission. A trained technician will check the level and condition of your transmission fluid:

  • A low fluid level may indicate a leak
  • Contaminated fluid has water or particles in the fluid.
  • Burnt fluid indicates damage from overheating.
  • Varnished fluid has been overheated repeatedly.
  • Normal fluid is reddish-brown and translucent, depending on transmission type, with no particular odor.

The technician will also check the level and condition of transfer case and differential fluid, where applicable. The technician takes your car on a road test, to experience first-hand any problems you have noticed, and to evaluate your car's performance. Your vehicle will be placed on a lift to inspect the controls under the vehicle for any possible cause of the problem external to the transmission. Finally, the technician will scan the computer for trouble codes*.

From these tests, the expert transmission technicians at AAMCO centers can determine what type of problem you might have, and make a recommendation for whatever service is necessary. That comprehensive approach to diagnosing the source of the problem is what sets AAMCO apart.

Locally owned and proudly operated by Pat and Jaye Patton

AAMCO San Marcos, TX


1206 Highway 123, San Marcos, TX 78666

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Monday - Friday | 08:00 AM - 06:00 PM

Saturday | 08:00 AM - 12:00 PM

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