What Does P1790 Mean?
The transmission control module has detected a mechanical failure affecting both first gear and second gear operation. This indicates significant internal transmission damage to components shared by these gear ranges, such as clutch packs or planetary gears.
Safety Warning
Vehicle will have severely compromised drive capability and may not move properly. Unsafe for continued operation and should be towed to repair facility.
Common Causes
35%
Worn or damaged low/reverse clutch pack
30%
Failed intermediate clutch pack or band
20%
Damaged planetary gear set components
10%
Severe transmission fluid contamination causing multiple component failures
5%
Failed one-way clutch or sprag preventing proper gear engagement
Diagnostic Steps
1
Step 1: Check transmission fluid level and condition for metal particles or severe contamination
2
Step 2: Attempt manual gear engagement in first and second to confirm mechanical failure
3
Step 3: Perform transmission pressure test to identify hydraulic system integrity
4
Step 4: Conduct stall test to evaluate clutch pack holding capability
5
Step 5: Drop transmission pan and inspect for metal debris, clutch material, or component damage
Estimated Repair Cost
$1,800 - $4,800
Parts + labor, varies by vehicle and location
The transmission control module has detected a mechanical failure affecting both first gear and second gear operation. This indicates significant internal transmission damage to components shared by these gear ranges, such as clutch packs or planetary gears.
The most common cause of P1790 (Transmission Mechanical Failure - First And Second) is: Worn or damaged low/reverse clutch pack
Typical repair costs for P1790 range from $1,800 to $4,800, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle will have severely compromised drive capability and may not move properly. Unsafe for continued operation and should be towed to repair facility.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1790 to identify the root cause.
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Quick Info
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Powertrain
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Transmission
Difficulty
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