Diagnostic trouble code P1718 is a manufacturer-specific powertrain fault code. Because it is manufacturer-specific, its exact definition depends entirely on the vehicle application, ranging from sensor performance issues to network communication faults.
Exact vehicle application must be verified before beginning diagnosis. The code identifies a detected condition within the Automatic Transmission system, but further testing is required to identify the root cause.
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Key Takeaways
- P1718 is a manufacturer-specific code, meaning its exact definition varies significantly between automakers like Ford, Subaru, Toyota, and GM.
- Possible causes depend on the specific vehicle and may include a failing transmission fluid temperature sensor, CAN bus wiring faults, or output speed sensor issues.
- Symptoms vary by application but can include erratic shifting, illuminated warning lights, or the transmission entering a fail-safe mode.
- Diagnosis requires verifying the exact factory definition for the specific vehicle and following the manufacturer’s targeted electrical or network testing procedures.
- Repairs depend on the confirmed root cause and may involve repairing wiring, replacing a specific sensor, or addressing module communication faults.
P1718 Code Description and Implications
Because P1718 is manufacturer-specific, there is no single universal definition. The exact monitored system and fault condition depend on the vehicle make and model.
Certain Ford applications: P1718 typically indicates a “Transmission Fluid Temperature (TFT) Sensor In-Range Failure.” The module detects that the TFT sensor is reporting an electrically valid but implausibly high or low temperature reading.
Some Subaru applications: P1718 often designates an “Automatic Transmission CAN Communication Circuit” fault. The transmission control module detects a loss of communication or a data corruption issue on the high-speed CAN bus network.
Specific Toyota applications: P1718 can indicate a “Transmission Output Speed Sensor” malfunction, where the module detects an illogical or missing signal from the output shaft speed sensor.
Certain GM/Chevrolet applications: P1718 may refer to a “Neutral Gear Ratio Error,” indicating the transmission control module detected an incorrect gear ratio while the vehicle was commanded into neutral.
Common Causes of the P1718 Code
The underlying cause depends entirely on the verified factory definition for the specific vehicle application.
For applications monitoring the TFT sensor, possible causes include a degraded internal thermistor, contaminated transmission fluid, or genuine transmission overheating.
For applications monitoring CAN communication, causes often involve damaged wiring harnesses, corroded connectors, electrical interference, or a failing control module.
For applications monitoring speed sensors or gear ratios, causes may include a failed speed sensor, damaged reluctor ring, internal mechanical wear, or low fluid levels.
Symptoms Associated With P1718
Symptoms vary widely depending on the underlying system fault and the vehicle manufacturer.
On applications with a TFT sensor fault, the transmission may default to a fail-safe shifting strategy, resulting in harsh or delayed shifts to protect the gearbox.
On applications with a CAN communication fault, the vehicle may experience severe drivability issues, erratic shifting, or multiple warning lights illuminating due to the loss of critical module data.
MIL behavior varies by application. Some vehicles may illuminate the Check Engine Light immediately, while others may store the code without commanding the light until the fault occurs over multiple drive cycles.
Diagnosing the P1718 Trouble Code
Diagnosis must begin by confirming the exact factory definition for the specific make, model, and year. Attempting to diagnose a CAN bus fault on a vehicle where P1718 indicates a TFT sensor issue will lead to misdiagnosis.
For TFT sensor applications, technicians typically compare the live data TFT reading against the engine coolant temperature after the vehicle has sat overnight. The wiring harness and sensor resistance are then tested against manufacturer specifications.
For CAN communication applications, diagnosis involves checking the network topology, inspecting the wiring harness for shorts or opens, and verifying module termination resistances using an oscilloscope or advanced scan tool.
Repairing the P1718 Issue
Repairs must follow confirmed diagnosis based on the specific vehicle application.
If testing confirms a failed TFT sensor or contaminated fluid, the sensor must be replaced or the fluid and filter must be serviced using the correct manufacturer-specified materials.
If a CAN communication fault is confirmed, repairing the damaged wiring, cleaning corroded connectors, or replacing a faulty control module may be required.
If an output speed sensor or gear ratio fault is confirmed, the sensor, internal mechanical components, or fluid levels must be addressed according to the manufacturer service information.
Cost Considerations for P1718 Repairs
Repair costs depend entirely on the confirmed root cause, component accessibility, and local labor rates.
Replacing an external sensor or repairing a section of wiring may require minimal parts and labor. Conversely, diagnosing complex network communication faults or replacing internal transmission components requires significant diagnostic time and specialized equipment.
Prevention Strategies for Future Occurrences
Some electrical or internal mechanical failures cannot be reliably prevented. However, maintaining the correct transmission fluid level and condition helps prevent sensor contamination and mechanical wear.
Ensuring that underbody wiring harnesses and module connectors remain sealed and protected from moisture and road debris can help reduce the likelihood of network communication faults.
Troubleshooting Tips and Best Practices
Never assume P1718 is a universal transmission communication code. Always verify the exact definition for the specific vehicle before purchasing parts or beginning electrical testing.
Do not ignore related codes. A CAN communication fault will often trigger a generic P0700 code alongside specific module communication codes, which help pinpoint the exact node failing on the network.
Check for technical service bulletins applicable to your exact vehicle application, as manufacturers frequently release updated wiring harnesses, sensor revisions, or software recalibrations for recurring transmission faults.
More OBD-II Codes
| P1716 | P1720 | P0700 | P0750 |
| P1715 | P1727 | U0101 | P0755 |
| P1714 | P1738 | U0073 | P0760 |
| P1713 | P1739 | P0717 | P0765 |
| P1712 | P1745 | P0770 | P0775 |
| P1711 | P1747 | P0780 | P0785 |
Frequently Asked Questions
Is P1718 a generic or manufacturer-specific code?
No. P1718 is a manufacturer-specific code. Its exact definition varies significantly between automakers, so the factory service information for the specific vehicle must be consulted.
Can I drive my car with a P1718 code?
It depends on the application and symptoms. If the transmission has entered a fail-safe mode or is shifting erratically, driving the vehicle could cause further damage or create a safety hazard.
Will disconnecting the battery clear the P1718 code?
Disconnecting the battery may temporarily clear the code, but it does not repair the underlying electrical or mechanical fault. The code will return once the module runs its self-test.
Can low transmission fluid cause a P1718 code?
On applications where P1718 indicates a gear ratio or speed sensor fault, low or degraded fluid can affect hydraulic pressure and sensor readings, potentially contributing to the fault condition.
Does P1718 always mean the transmission control module is bad?
No. While a failing module can cause communication or sensor faults, wiring damage, connector corrosion, or failed external sensors are frequent causes that must be ruled out first.
What Should You Do About the P1718 Code?
Confirm the exact factory definition and diagnostic procedure for your specific vehicle application. Because P1718 is manufacturer-specific, identifying whether it relates to a temperature sensor, network communication, or speed sensor is the mandatory first step.
Follow the applicable manufacturer diagnostic steps to test the relevant system and components. Once the root cause is confirmed, complete the necessary repairs and verify that the transmission operates correctly and the code does not return.
