Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
This code means that the car's computer is using a backup plan because something isn't working right. It's like when you use a flashlight on your phone because the lights went out.
The vehicle's transmission control module (TCM) has detected a fault and has switched to a substitute function to maintain drivability.
P1799 indicates that the TCM has prioritized a substitute function due to a detected fault in the transmission system. This allows the vehicle to continue operating, albeit with limited functionality, to prevent further damage.
• Check Engine Light is on
• Transmission may not shift properly
• Reduced fuel efficiency
• Faulty transmission control module
• Wiring issues in the transmission system
• Malfunctioning sensors related to the transmission
TCM: Transmission Control Module
OBD-II: On-Board Diagnostics, Second Generation
• Use an OBD-II scanner to confirm the code
• Inspect the wiring and connectors for damage
• Test the transmission control module for faults
• Repair or replace damaged wiring
• Replace faulty sensors
• Replace or reprogram the transmission control module
• OBD-II scanner
• Multimeter
• Basic hand tools
$200 - $1000
Moderate
• Honda Accord
• Toyota Camry
• Ford Focus
• Regular transmission fluid changes
• Routine inspection of wiring and connectors
• Timely servicing of the transmission system
Transmission Control System Issue
• Avoid driving aggressively until the issue is resolved
• Schedule a diagnostic check with a professional mechanic
Transmission components may be covered under the powertrain warranty, typically 5 years or 60,000 miles.
This code has been associated with various transmission issues across different vehicle models, often requiring TCM reprogramming.
Moderate – It is advisable to address this issue soon to prevent further transmission damage.
Driving with a malfunctioning transmission can be unsafe and may lead to further damage. Address the issue promptly.
• Vehicle must be driven to replicate the issue
• Transmission temperature should be within normal operating range
The transmission control module is typically located near the transmission or inside the engine bay.
Q: Can I drive with a P1799 code?
A: While the vehicle may still be drivable, it is not recommended to drive long distances as it can cause further damage.
Q: Will clearing the code fix the problem?
A: Clearing the code may temporarily remove the warning light, but it won't fix the underlying issue.
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