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 computer inside the car that helps control the transmission is having trouble keeping track of what it's supposed to do. It's like when your computer freezes and you have to restart it.
The Transmission Control Module (TCM) has detected an internal fault, specifically related to its watchdog function, which monitors the module's operations.
The P171A code indicates a malfunction in the internal watchdog function of the Transmission Control Module (TCM). This watchdog function is responsible for ensuring that the TCM's operations are running smoothly and without errors. If the watchdog detects an issue, it triggers this fault code.
• Check Engine Light is on
• Transmission may not shift properly
• Vehicle may enter limp mode
• Faulty Transmission Control Module (TCM)
• Software glitch in the TCM
• Electrical issues such as poor connections or damaged wiring
Transmission Control Module (TCM): An electronic component that controls the transmission functions.
Watchdog: A system that monitors the operation of a device to ensure it is functioning correctly.
• Use an OBD-II scanner to confirm the code.
• Inspect the TCM for any visible damage or loose connections.
• Check for any software updates for the TCM.
• Reprogram or update the TCM software.
• Repair or replace damaged wiring or connectors.
• Replace the Transmission Control Module if necessary.
• OBD-II scanner
• Multimeter
• Basic hand tools
$300 - $1200
Moderate
• Ford Focus
• Chevrolet Malibu
• Dodge Charger
• Regularly update vehicle software.
• Ensure good electrical connections.
• Avoid harsh driving conditions that may stress the transmission.
Transmission Control Module Issue
• Do not ignore the Check Engine Light.
• Have the vehicle inspected by a professional if you notice transmission issues.
Check with your vehicle manufacturer as TCM issues may be covered under powertrain warranty.
This code has been associated with vehicles experiencing software-related issues in the TCM, often requiring updates or reprogramming.
Moderate – It's important to address this issue to prevent further transmission problems.
Driving with a faulty TCM can lead to unsafe driving conditions. It is advisable to have the issue diagnosed and repaired promptly.
• Vehicle at operating temperature
• Transmission in normal operating mode
The Transmission Control Module is typically located inside the engine bay or under the dashboard, depending on the vehicle model.
Q: Can I drive with a P171A code?
A: It's not recommended to drive for long periods with this code, as it may lead to further transmission issues.
Q: Will a software update fix the P171A code?
A: In some cases, a software update can resolve the issue, but it depends on the specific cause of the code.
High-End · Full-system diagnostics
A full-system bidirectional platform aimed at advanced DIY users and professional diagnostic workflows.
Network faults often require full-system access instead of a generic code reader alone.
View on Amazon
Universal · Digital multimeter
A solid entry-level multimeter for voltage, continuity, resistance, and basic electrical troubleshooting.
Helpful for checking voltage drops, grounds, and basic circuit health when modules are not communicating.
View on Amazon
Universal · Wire connectors and repair kit
Useful when diagnosis points toward damaged wiring, corroded terminals, or connector repairs.
Useful if diagnosis points toward damaged connectors, wiring, or terminal repairs.
View on AmazonThese are optional diagnostic tools, not guaranteed fixes. As an Amazon Associate I earn from qualifying purchases.