P1713

What Does Code P1713 Mean?

The diagnostic trouble code P1713, “TFT Sensor In Range Failure Low Value,” indicates that the Powertrain Control Module (PCM) or Transmission Control Module (TCM) has detected an anomaly with the Transmission Fluid Temperature (TFT) sensor’s signal. Specifically, the PCM/TCM is receiving a signal from the TFT sensor that, while technically within the sensor’s plausible electrical operating range (not an open circuit or short to ground), consistently reports a transmission fluid temperature that is significantly lower than what would be expected under the current operating conditions. This discrepancy is often determined by comparing the TFT reading against other temperature sensors (such as Engine Coolant Temperature and Intake Air Temperature) at cold start, or by monitoring its behavior during vehicle operation and warm-up. The TFT sensor is a thermistor that changes its electrical resistance in response to temperature variations. A typical Negative Temperature Coefficient (NTC) thermistor used in automotive applications will exhibit higher resistance at lower temperatures and lower resistance at higher temperatures. The PCM/TCM supplies a reference voltage (typically 5V) to the sensor through a pull-up resistor and monitors the voltage drop across the sensor. If the sensor’s resistance is abnormally high (even at normal operating temperatures), the voltage signal sent back to the PCM/TCM will be higher than expected, leading the control module to misinterpret the fluid temperature as being colder than it actually is. This erroneous low-temperature reading can critically impact the transmission’s shift strategy, torque converter lock-up control, and overall operational efficiency, as the PCM/TCM relies on accurate fluid temperature data for optimal performance and protection.

Common Symptoms

• Delayed or Harsh Gear Shifts: The PCM/TCM may delay shifts or increase line pressure, especially when the transmission is supposedly “cold,” to protect components, leading to noticeable shift quality issues.
• Erratic or Non-Operating Torque Converter Lock-Up: The PCM/TCM might prevent the torque converter from locking up, or engage/disengage it inconsistently, if it believes the fluid is too cold, impacting fuel economy and vehicle performance.
• Reduced Fuel Economy: Due to delayed shifts and/or the absence of torque converter lock-up, the engine may operate at higher RPMs for longer periods.
• Illuminated Malfunction Indicator Lamp (MIL): The “Check Engine” light will illuminate on the dashboard to alert the driver of a detected issue.
• Transmission May Not Reach Operating Temperature: While the fluid itself might be at proper temperature, the erroneous low reading could prevent the PCM from exiting its “cold” operating strategy.

What Causes the Code P1713?

• Faulty Transmission Fluid Temperature (TFT) Sensor: This is the most prevalent cause. The thermistor element within the sensor itself may have degraded, causing its internal resistance to be abnormally high at actual operating temperatures. This high resistance results in a higher-than-expected voltage signal being sent to the PCM/TCM, which interprets it as a lower-than-actual fluid temperature.
• Wiring Harness Issues:
  • High Resistance in the Sensor Signal Circuit: Corrosion, loose connections, or a partial break within the signal wire leading from the TFT sensor to the PCM/TCM can introduce excessive resistance into the circuit. This elevated resistance can cause the voltage signal reaching the control module to be artificially higher than it should be for the actual fluid temperature, leading to a “low value” (low temperature) reading.
  • High Resistance in the Sensor Ground Circuit: Similarly, a poor or corroded ground connection for the TFT sensor can elevate the entire sensor’s voltage potential, resulting in an artificially high signal voltage at the PCM/TCM input, interpreted as a low temperature.
• Corroded or Damaged Connector Pins: Oxidation or physical damage to the electrical pins within the TFT sensor connector or the corresponding PCM/TCM connector can lead to increased circuit resistance, mimicking a wiring harness issue.
• Transmission Control Module (TCM)/Powertrain Control Module (PCM) Failure: Although rare, an internal fault within the control module itself could cause it to incorrectly interpret the sensor’s signal, provide an erroneous reference voltage, or improperly process the resistance value. This should only be considered after exhaustive testing of the sensor and wiring.

How to Diagnose and Troubleshoot

Diagnosing P1713 requires a methodical approach, utilizing an OBD-II scanner with live data capabilities and a digital multimeter (DMM).

1. Initial Scan and Freeze Frame Data Analysis:
   • Connect an OBD-II scanner and confirm the presence of P1713.
   • Note any other related DTCs, as they might provide additional clues.
   • Review the freeze frame data associated with P1713. Pay close attention to the reported TFT, ECT (Engine Coolant Temperature), IAT (Intake Air Temperature), engine speed, and vehicle speed at the time the code was set. This provides a snapshot of conditions during the fault.
2. Visual Inspection:
   • Carefully inspect the TFT sensor connector and the entire wiring harness leading from the sensor back to the PCM/TCM. Look for signs of damage, fraying, kinks, chafing, melted insulation, or corrosion.
   • Verify that the sensor connector is securely seated and not loose. Check for bent, pushed-out, or corroded pins within the connectors.
3. Live Data Monitoring (Cold Start):
   • With the engine cold (e.g., after sitting overnight), use the OBD-II scanner to monitor live data for the TFT, ECT, and IAT sensors. All three readings should be very close to ambient air temperature.
   • If the TFT reading is significantly lower than the ECT and IAT (e.g., 20°F lower), even at ambient temperature, this strongly suggests a faulty TFT sensor or a problem in its circuit causing an artificially low temperature reading.
4. Live Data Monitoring (Warm-Up & Drive Cycle):
   • Start the engine and allow it to warm up. Monitor the TFT reading as the engine and transmission fluid temperature rises.
   • The TFT value should increase steadily and eventually stabilize near the ECT value during normal operation.
   • If the TFT reading remains stubbornly low or rises very slowly compared to the ECT, even after extended driving, this reinforces the suspicion of a faulty sensor or circuit.
5. Resistance Test of TFT Sensor (Component Test):
   • Disconnect the TFT sensor electrical connector.
   • Using a DMM set to ohms, measure the resistance across the two terminals of the TFT sensor itself.
   • Compare this reading to the manufacturer’s specified resistance-temperature chart for your specific vehicle (found in service manuals). Ensure the sensor is at a known temperature (e.g., ambient shop temperature) during the test.
   • An abnormally high resistance reading (higher than specified for the current temperature) indicates an internal fault within the sensor, causing it to report a low temperature.
6. Circuit Voltage and Resistance Tests (Wiring Integrity):
   • With the ignition ON and the sensor disconnected, use a DMM to test for the 5V reference voltage at one of the sensor’s harness connector terminals.
   • Test the ground circuit at the other terminal for continuity to chassis ground (should be very low resistance, typically < 0.5 ohms).
   • Reconnect the sensor. Backprobe the signal wire at the sensor connector (if accessible) or at the corresponding pin at the PCM/TCM connector. With the ignition ON, measure the signal voltage. As discussed, a “low value” code suggests a higher-than-expected voltage for the actual temperature.
   • If the sensor resistance tests good, perform a resistance check of the signal and ground wires from the sensor connector back to the PCM/TCM connector. Look for excessive resistance (> 1 ohm) in either wire, indicating a potential open or poor connection.

Recommended Repairs and Solutions

Based on the diagnostic findings, the following repairs are typically effective:

• Replace the Transmission Fluid Temperature (TFT) Sensor: This is by far the most common resolution for P1713. If the sensor’s resistance is out of specification or its live data readings are consistently low, replacement is necessary. Ensure you use an OEM-quality replacement part to ensure accuracy and longevity. When replacing, ensure proper sealing and torque if the sensor threads into the transmission case, and check the transmission fluid level afterwards.
• Repair or Replace Damaged Wiring Harness: If the visual inspection or DMM tests reveal high resistance, corrosion, or damage in the wiring harness or connectors, perform precise repairs. Use appropriate heat-shrink butt connectors for durable wiring splices. For severely damaged sections, consider replacing the entire pigtail or harness section. Ensure all connections are clean and secure.
• Clean Corroded Connector Pins: If corrosion is found at the sensor or PCM/TCM connectors, carefully clean the pins using specialized electrical contact cleaner and a small brush. Ensure all pins make firm contact once reconnected.
• Address PCM/TCM Fault (Last Resort): If, and only if, the TFT sensor and all associated wiring and connectors have been thoroughly tested and confirmed to be in perfect working order, and the P1713 code persists, then a faulty PCM/TCM might be considered. This is a rare and expensive repair, often requiring reprogramming after installation.

After completing any repair, clear the DTCs using an OBD-II scanner. Perform an extended drive cycle, including varied driving conditions, to allow the PCM/TCM to re-evaluate the TFT sensor’s operation. Monitor live data during this drive to confirm that the TFT readings are now accurate, stable, and correlate correctly with other temperature sensors as the transmission warms up.