Fixing Mazda Transmission Downshifting on Highways

Make: Mazda | Model example: 2010 3 | Avg Mileage: 117433 | Job Number: 483388

Repair Issue:

Transmission Internittently Downshifting At Highway Speeds

Cause:

Transmission control module (TCM) and/or wiring harness

Customer Concern:

Intermittently while cruising at highway speeds, the transmission will downshift in to 3rd gear and the check transmission warning light comes on. Sets a code P0753 indicating an electrical circuit fault of the shift solenoid A. Has a new shift solenoid installed but the code still returns.

Test/Procedure:

1. Closely inspect the connectors terminals at the Transmission Control Module (TCM) and the transmission.
2. Inspect the internal transmission wiring harness and ground eyelet for Shift Solenoid A. Apply battery voltage to the terminals in the transmission connector and do an amp draw test on the solenoid A circuit and compare it to the shift solenoid B circuit. Both solenoids should draw the same amount of current. If both solenoid circuits test the same, the problem is not internal to the transmission.
3. If this is not an internal transmission wiring harness issue, you could run a new wire between the TCM and the transmission solenoid connector at the case of the transmission to eliminate that wire as a problem. If this is not a wiring issue and the code still returns, it could have a faulty Transmission Control Module (TCM).

Tech Tip:

This applies to a 5 speed automatic transmission. See the attached document for solenoid identification and wiring diagrams.

Important Take-A-Way:

Tech Tip narrows down transmission type and points mechanics to related documentation.

Most Popular Fix:

Replaced/Repaired/Tightened/Adjusted Transmission Control Module (TCM)

Other Common Car Problems:

View more common car problems from the most popular manufactures including Ford, Dodge, Chevrolet, Honda, Toyota, and more. Read more

Also applies to the following Makes and Models

3

Author: Guy Dibble

Guy began his automotive career in 1989. His experience includes working at Isuzu, Mazda, and Subaru dealerships as well as owning and operating an independent shop for two years. Guy grew up in his father’s automotive repair shop in Texas and has been working on cars since he was 14 years old. He went to Texas State Technical College after high school and obtained an Associate’s Degree in Automotive Technology. After tech school he worked in a multi line Japanese car dealership where he became familiar with Mazda, Subaru, Isuzu, Suzuki, Kia and Diahatsu. His specialty carlines were Mazda and Isuzu, both of which he is Master Certified in. He has his ASE Master Tech certification as well as the advanced L1. Outside side of work he enjoys fishing and mountain biking.

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