P2907 critical

Transmission Gear Ratio Error - Reverse

The P2907 code means the vehicle's onboard diagnostic system has detected: Transmission Gear Ratio Error - Reverse. This is a critical severity code.

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Keep driving?: No -- stop driving
DIY difficulty: hard
Estimated cost: $600 - $3,500 (parts and labor)

Check Your Fluid First

ANCEL AD310 OBD-II Scanner

Read and clear transmission codes. Many trans codes are caused by low or burnt fluid -- check level and color before assuming the worst.

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Read Transmission Codes

LAUNCH CRP123X (Reads All Systems)

Basic scanners only read engine codes. This reads transmission, ABS, and airbag too.

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Common Symptoms

No reverse gear engagement
Grinding noise in reverse
Check Engine Light on
Delayed or harsh reverse engagement

Probable Causes (Ranked by Likelihood)

Reverse clutch pack failure Very High
Reverse servo or band failure High
Manual valve linkage out of adjustment Moderate
Parking pawl interference Low

Step-by-Step Diagnostic Procedure

Test reverse engagement pressure
Inspect manual valve and linkage
Check reverse servo operation
Listen for abnormal noises during reverse engagement

Frequently Asked Questions

What causes a gear ratio error?

A gear ratio error occurs when the TCM detects that the actual gear ratio (calculated from input and output speed sensors) does not match the expected ratio for the commanded gear. This can indicate clutch slippage, speed sensor issues, or internal mechanical failure.

Is this a transmission rebuild situation?

Not necessarily. While internal clutch failure requires major repair, this code can also be caused by speed sensor inaccuracy, low fluid, or valve body issues that are less costly to repair. Proper diagnosis is essential before assuming a rebuild is needed.

Why would reverse fail specifically?

Reverse uses a dedicated clutch pack and may have a separate servo mechanism. These components can fail independently of the forward gears, especially in high-mileage vehicles.