P0713

What Does Code P0713 Mean?

The diagnostic trouble code P0713 signifies a detected malfunction within the Transmission Fluid Temperature Sensor (TFTS) circuit, specifically indicating a “High Input” condition. The Engine Control Module (ECM) or Powertrain Control Module (PCM) monitors the voltage signal from the TFTS to determine the transmission fluid’s operating temperature. The TFTS is typically a thermistor, usually of the Negative Temperature Coefficient (NTC) type, where its electrical resistance decreases as the fluid temperature increases, and vice-versa. The PCM supplies a reference voltage (commonly 5V) to the TFTS, which acts as a variable resistor within a voltage divider circuit. As the fluid temperature changes, the sensor’s resistance changes, causing a corresponding change in the voltage signal returned to the PCM.

A “High Input” error, in the context of an NTC thermistor, means the voltage signal the PCM receives from the TFTS circuit is unexpectedly high. This typically corresponds to an extremely high resistance within the sensor circuit, suggesting an implausibly low fluid temperature (e.g., -40°F / -40°C) or, more commonly, an open circuit in the sensor itself or its wiring. When the PCM detects this abnormally high voltage signal exceeding its calibrated maximum threshold for a specified duration, it sets the P0713 code. This subsystem directly affects transmission shift strategies, torque converter clutch (TCC) engagement, line pressure control, and overall transmission efficiency, as the PCM relies on accurate fluid temperature data to optimize these functions. In response to the fault, the PCM will often revert to a default calculated temperature value or engage a “limp mode” to protect the transmission.

Common Symptoms

• Malfunction Indicator Lamp (MIL) Illumination: The “Check Engine” light will be illuminated on the dashboard.
• Harsh or Erratic Shifting: The transmission may engage gears abruptly or at unusual points.
• Delayed Gear Engagement: A noticeable delay when shifting into drive or reverse from park or neutral.
• Transmission Limp Mode: The transmission may lock into a single gear (often 2nd or 3rd) to prevent damage.
• Torque Converter Clutch (TCC) Malfunction: Failure of the TCC to engage or disengage, potentially leading to increased engine RPM at highway speeds or shuddering.
• Increased Fuel Consumption: Inefficient shifting and TCC operation can lead to reduced fuel economy.
• Absence of Overdrive: The transmission may not shift into its highest gear ratio.
• Erroneous Temperature Gauge Readings: If the vehicle features a transmission fluid temperature gauge, it may display an incorrect or fixed extremely low reading.

What Causes the Code P0713?

• Faulty Transmission Fluid Temperature Sensor (TFTS): The most common cause, including an internal open circuit, excessive resistance, or damaged thermistor element within the sensor itself.
• Open Circuit in TFTS Wiring: A break or discontinuity in the signal wire or ground wire connecting the TFTS to the PCM.
• Short to Voltage in TFTS Circuit: The signal wire inadvertently contacting a power source (e.g., 12V supply), causing the high input reading.
• Corroded or Damaged Electrical Connector: Poor connection at the TFTS connector due to corrosion, bent pins, or physical damage, leading to an intermittent or open circuit.
• Faulty Transmission Internal Wiring Harness: Many TFTS units are integrated into the internal transmission wiring harness, which can degrade or become damaged over time.
• ECM/PCM Failure: While rare, an internal fault within the PCM affecting the sensor reference voltage supply or input monitoring circuit can cause this code.

How to Diagnose and Troubleshoot

Diagnosis of P0713 requires a methodical approach, utilizing an OBD-II scanner, a digital multimeter (DMM), and visual inspection.

1. Initial Scan and Data Analysis:
   • Connect an OBD-II scanner to retrieve all stored and pending Diagnostic Trouble Codes (DTCs). Note any other transmission-related codes, as they may offer additional context.
   • Clear the P0713 code and perform a short test drive, if possible, to see if the code immediately returns.
   • Access live data parameters and monitor the “Transmission Fluid Temperature” (TFT) reading. If the sensor circuit is open, the TFT reading will often be stuck at an extremely low, implausible value (e.g., -40°F / -40°C) or at a default value.
2. Visual Inspection:
   • Carefully inspect the external transmission wiring harness for any signs of physical damage, chafing, cuts, or corrosion, especially where it connects to the transmission case. Pay close attention to the TFTS connector itself for loose terminals, bent pins, or signs of fluid intrusion.
   • Check the transmission fluid level and condition. Extremely dirty or low fluid can sometimes contribute to sensor issues, though it’s less direct for a high input.
3. TFTS Resistance Check (if externally accessible):
   • Locate and disconnect the electrical connector from the TFTS.
   • Using a DMM set to ohms (Ω), measure the resistance across the two terminals of the TFTS itself.
   • Compare this reading to the manufacturer’s specified resistance values for the ambient or current transmission fluid temperature. An open circuit will read “OL” or infinite resistance, confirming a faulty sensor. A reading significantly higher than specified also indicates a fault.
4. Circuit Voltage and Continuity Checks (at TFTS connector):
   • Reference Voltage: With the ignition ON (engine OFF), disconnect the TFTS connector. Using the DMM set to DC volts, carefully probe the signal wire terminal at the harness side connector (coming from the PCM), referencing a known good chassis ground. You should typically measure approximately 5 Volts. A missing or incorrect voltage indicates a wiring issue back to the PCM or a PCM fault.
   • Ground Circuit: Switch the DMM to ohms. Probe the ground wire terminal at the harness side connector and measure its continuity to a known good chassis ground. You should read very low resistance (near 0 ohms). An open circuit (OL) indicates a break in the ground wire.
5. Circuit Integrity Check (between TFTS connector and PCM):
   • Disconnect both the TFTS connector and the PCM connector.
   • Check for continuity of the signal wire and ground wire between their respective pins at the TFTS harness connector and the corresponding pins at the PCM harness connector using the DMM set to ohms. You should read very low resistance.
   • Also, check for shorts to ground (between the signal wire and chassis ground) and shorts to voltage (between the signal wire and any power wire) on both the signal and ground wires. Any short circuit indicates damaged wiring.

Recommended Repairs and Solutions

Once the diagnostic steps have pinpointed the root cause, the appropriate repair can be implemented:

• Replace the Transmission Fluid Temperature Sensor (TFTS): This is the most frequent repair. Many TFTS units are integrated into the transmission’s internal wiring harness or valve body assembly. Replacing it often requires draining the transmission fluid, removing the transmission pan, and potentially the valve body. Always use an OEM equivalent or direct-fit aftermarket sensor for reliable performance.
• Repair or Replace Damaged Wiring: If the wiring harness (either external or internal to the transmission) is found to be open, shorted, or corroded, repair the specific damaged section using appropriate automotive-grade wire, solder, and heat-shrink tubing. If the damage is extensive, replacing the entire harness segment is advisable.
• Clean or Replace Corroded Connectors: If corrosion is found at the TFTS or PCM connector pins, carefully clean them using an electrical contact cleaner and a small brush. Apply dielectric grease to prevent future corrosion upon reassembly. If pins are severely damaged, re-pinning the connector or replacing the entire connector housing may be necessary.
• PCM Replacement: This should only be considered as a last resort, after all other components and wiring have been thoroughly tested and ruled out as the cause. If the PCM is determined to be faulty, ensure that the replacement module is properly programmed and calibrated to the vehicle’s specific VIN and options.

Mechanics’ Tips:

• Always consult the vehicle-specific factory service manual for precise wiring diagrams, TFTS location, resistance specifications at various temperatures, and connector pinouts. These details are crucial and vary greatly by manufacturer and model.
• When performing internal transmission work, maintain absolute cleanliness to prevent contaminants from entering the transmission fluid system.
• After replacing an internal TFTS, ensure the transmission fluid is refilled to the correct level using the specified fluid type, and that the fluid temperature is checked as per manufacturer’s instructions.
• Following any repair, clear the DTCs with an OBD-II scanner and perform an extended test drive to confirm the P0713 code does not return and that the transmission operates normally, with accurate TFT readings in live data.