P0718 - Input/Turbine Speed Sensor Circuit Intermittent

Introduction:

The P0718 diagnostic trouble code (DTC) indicates an intermittent fault within the circuit of the input or turbine speed sensor (ISS/TSS) in your vehicle's automatic transmission. This sensor plays a crucial role in monitoring the rotational speed of the transmission's input shaft, providing vital data to the powertrain control module (PCM) or transmission control module (TCM) for proper gear selection and transmission operation. Addressing this code promptly is essential to prevent potential drivability issues and further damage to the transmission.

Table: P0718 - Input/Turbine Speed Sensor Circuit Intermittent

Category	Description	Possible Solutions
Sensor Function	Measures the rotational speed of the transmission's input or turbine shaft. Provides data to the PCM/TCM for shift timing, torque converter clutch (TCC) engagement, and overall transmission control. This input is critical for determining engine load and optimizing transmission performance. Some vehicles may also use this data for cruise control or traction control systems.	No direct solution, understanding the function helps diagnose the root cause.
Symptoms	Erratic shifting: Hard shifts, delayed shifts, or failure to shift. Transmission slipping: Engine RPM increases without a corresponding increase in vehicle speed. Torque converter clutch (TCC) issues: Failure to engage or disengage, resulting in poor fuel economy and performance. Check Engine Light (CEL) illumination: The P0718 code triggers the CEL. Stalling: In some cases, the vehicle may stall, especially at low speeds. Limp mode: The transmission may enter a limited-function mode to prevent further damage. * Reduced fuel economy	Address the root cause of the sensor malfunction. Repair the circuit or replace the sensor.
Possible Causes	Faulty ISS/TSS sensor: The sensor itself may be defective. Wiring issues: Damaged, corroded, or loose wiring or connectors in the sensor circuit. Circuit shorts or opens: A short to ground or voltage, or an open circuit in the sensor wiring. PCM/TCM failure: In rare cases, a faulty PCM/TCM may be misinterpreting the sensor signal. Metal debris: Excessive metal debris in the transmission fluid can interfere with the sensor's operation. Low or contaminated transmission fluid: Insufficient fluid level or degraded fluid can affect transmission performance and sensor readings.	Identify the root cause through diagnostic testing. Repair or replace faulty components. Flush and refill transmission fluid if needed.
Diagnostic Steps	1. Retrieve the DTC: Use an OBD-II scanner to confirm the P0718 code and any other related codes. 2. Inspect the sensor and wiring: Visually inspect the sensor, wiring harness, and connectors for damage, corrosion, or loose connections. 3. Check transmission fluid level and condition: Ensure the fluid is at the proper level and is clean and free of debris. 4. Test the sensor: Use a multimeter to check the sensor's resistance and output voltage. Compare readings to manufacturer specifications. 5. Check the wiring circuit: Use a multimeter to check for continuity, shorts to ground, and shorts to voltage in the sensor wiring. 6. Perform a wiggle test: With the engine running, gently wiggle the sensor wiring and connectors to see if the signal fluctuates. 7. Scan tool data analysis: Use a scan tool to monitor the ISS/TSS signal in real-time while driving the vehicle. 8. PCM/TCM diagnosis: If other tests are inconclusive, the PCM/TCM may need to be tested by a qualified technician.	Replace faulty sensor, Repair/replace damaged wiring/connectors, Flush/replace transmission fluid, Replace PCM/TCM (rare).
Common Mistakes	Replacing the sensor without proper diagnosis: Ensure the sensor is actually faulty before replacing it. Ignoring wiring issues: Wiring problems are a common cause of P0718. Neglecting transmission fluid: Low or contaminated fluid can cause a variety of transmission problems. Assuming PCM/TCM failure prematurely: PCM/TCM failure is rare; thoroughly test other components first.	Conduct thorough diagnostics, Inspect wiring carefully, Check transmission fluid level and condition, Rule out other potential causes.
Tools Required	OBD-II scanner Multimeter Wiring diagrams Socket set Wrench set Transmission fluid funnel Jack and jack stands (if necessary) Contact cleaner * Penetrating oil	N/A
Related DTCs	P0715 (Input/Turbine Speed Sensor Circuit Malfunction), P0716 (Input/Turbine Speed Sensor Circuit Range/Performance), P0717 (Input/Turbine Speed Sensor Circuit No Signal), P0720 (Output Speed Sensor Circuit), P0721 (Output Speed Sensor Circuit Range/Performance), P0722 (Output Speed Sensor Circuit No Signal), P0723 (Output Speed Sensor Intermittent)	N/A

Detailed Explanations:

Sensor Function: The input/turbine speed sensor (ISS/TSS) is an electromagnetic sensor located near the transmission's input shaft. As the input shaft rotates, a toothed reluctor wheel passes by the sensor, generating an alternating current (AC) signal. The frequency of this signal is directly proportional to the rotational speed of the input shaft. The PCM/TCM uses this information to determine the transmission's gear ratio, monitor slippage, and control the torque converter clutch (TCC). Without accurate input speed data, the transmission may not shift correctly, leading to performance issues and potential damage.

Symptoms: The symptoms of a P0718 code can vary depending on the severity of the fault and the specific vehicle. Erratic shifting is a common symptom, manifesting as hard shifts, delayed shifts, or a complete failure to shift gears. Transmission slipping, where the engine RPM increases without a corresponding increase in vehicle speed, is another telltale sign. Problems with the torque converter clutch (TCC), such as failure to engage or disengage, can also occur. The Check Engine Light (CEL) will illuminate, and the vehicle may enter limp mode to protect the transmission. In some cases, the vehicle may stall, particularly at low speeds, and fuel economy can suffer.

Possible Causes: A faulty ISS/TSS sensor is a primary suspect. The sensor itself may have failed internally. Wiring issues, including damaged, corroded, or loose wiring or connectors in the sensor circuit, are also frequent culprits. Circuit shorts or opens can disrupt the sensor signal. While less common, a PCM/TCM failure can sometimes misinterpret the sensor signal. Metal debris in the transmission fluid can interfere with the sensor's magnetic field and affect its readings. Finally, low or contaminated transmission fluid can also impact transmission performance and sensor accuracy.

Diagnostic Steps: The first step is to retrieve the DTC using an OBD-II scanner to confirm the P0718 code and identify any other related codes that might provide additional clues. Next, inspect the sensor and wiring for any obvious signs of damage, corrosion, or loose connections. Checking the transmission fluid level and condition is crucial; ensure the fluid is at the proper level and appears clean and free of debris. Test the sensor using a multimeter to check its resistance and output voltage, comparing the readings to manufacturer specifications. Check the wiring circuit for continuity, shorts to ground, and shorts to voltage. Perform a wiggle test by gently wiggling the sensor wiring and connectors while the engine is running to see if the signal fluctuates. Use a scan tool to monitor the ISS/TSS signal in real-time while driving the vehicle. If other tests are inconclusive, the PCM/TCM may need to be tested by a qualified technician, although this is less common.

Common Mistakes: A frequent error is replacing the sensor without proper diagnosis. Always confirm that the sensor is actually faulty before replacing it. Ignoring wiring issues is another common mistake, as wiring problems are a frequent cause of P0718. Neglecting transmission fluid can also lead to misdiagnosis, as low or contaminated fluid can cause various transmission problems. Finally, assuming PCM/TCM failure prematurely is a mistake; PCM/TCM failure is relatively rare, so thoroughly test other components first.

Tools Required: Essential tools include an OBD-II scanner to read the DTCs, a multimeter to test the sensor and wiring, wiring diagrams to trace the sensor circuit, a socket set and wrench set for removing and installing components, a transmission fluid funnel for adding fluid, jack and jack stands (if necessary) to access the sensor, contact cleaner to clean electrical connections, and penetrating oil to loosen corroded fasteners.

Related DTCs: Several other DTCs can be related to P0718, including P0715 (Input/Turbine Speed Sensor Circuit Malfunction), P0716 (Input/Turbine Speed Sensor Circuit Range/Performance), P0717 (Input/Turbine Speed Sensor Circuit No Signal), P0720 (Output Speed Sensor Circuit), P0721 (Output Speed Sensor Circuit Range/Performance), P0722 (Output Speed Sensor Circuit No Signal), and P0723 (Output Speed Sensor Circuit Intermittent). These codes can provide additional information about the nature of the transmission problem.

Frequently Asked Questions:

What does the P0718 code mean? It indicates an intermittent fault in the input/turbine speed sensor circuit of your automatic transmission. This sensor measures the input shaft's speed.
Can I drive with a P0718 code? It's not recommended. Driving with a P0718 code can lead to erratic shifting, transmission damage, or even complete transmission failure.
How do I fix a P0718 code? The fix involves diagnosing the root cause, which could be a faulty sensor, wiring issues, or low transmission fluid. Repair or replacement of the affected component is then necessary.
Is the input/turbine speed sensor expensive to replace? The cost varies depending on the vehicle make and model, but the sensor itself is usually relatively inexpensive. Labor costs can be more significant.
Can low transmission fluid cause a P0718 code? Yes, low or contaminated transmission fluid can affect sensor readings and trigger the P0718 code.

Conclusion:

The P0718 code signifies an intermittent issue with the input/turbine speed sensor circuit, requiring careful diagnosis to identify the underlying cause. Addressing this code promptly and thoroughly is crucial to prevent further transmission damage and ensure optimal vehicle performance.