Comprehensive diagnostic guide for OBD-II code P0718

What This Code Means

• Primary definition: P0718 is described as an intermittent signal issue for the turbine inlet rotation sensor A (intermittent input/turbine speed sensor signal). This description comes from the Open Source code definitions provided in the materials you supplied. In context, this corresponds to an intermittent signal on the turbine/input speed sensor circuit (Input/Turbine Speed Sensor). Source citation: Open Source Code Definitions.

Context and where it fits in OBD-II

• OBD-II codes are diagnostic trouble codes used by modern vehicles to monitor engine and powertrain systems. They are generated by the vehicle's onboard computer when a parameter falls outside expected ranges or a sensor circuit is intermittent/different from expected values. This is described generally in the OBD-II Diagnostic Trouble Codes sections of the OBD-II articles (Powertrain Codes, Diagnostic Trouble Codes), which categorize codes as powertrain or emissions-related and explain the purpose of DTCs in fault detection and repair. Source citations: Wikipedia - OBD-II, Diagnostic Trouble Codes; Wikipedia - OBD-II, Powertrain Codes.

What This Code Means

• Given its designation as an intermittent turbine/input speed sensor signal, symptoms are often related to transmission input speed sensing only sporadically or under certain driving conditions. Real-world symptom descriptions reported by users (for related transmission speed sensor categories and intermittent sensor signals) commonly include:
  • Intermittent or inconsistent transmission shifting quality (late shifts, harsh shifts, or sudden downshifts) that appears and disappears as the sensor signal comes and goes.
  • Transmission may go into a fail-safe/limp mode intermittently, limiting certain gears or range until the fault clears.
  • Erratic or non-sync'd speedometer readings in some vehicles, especially if the turbine/input speed sensor is used as part of speed measurement for transmission control.
  • Check Engine/ABS/Transmission warning lights may illuminate depending on the vehicle's integration of the sensor signal into the powertrain control logic.
    Note: These symptom patterns are consistent with the generic role of turbine/input speed sensing in automated transmissions and the nature of intermittent signals. emphasize that DTCs indicate a monitored parameter deviating from expected behavior, and intermittent signals can produce temporary, non-continuous faults that trigger a stored DTC. Source citations: Wikipedia - OBD-II (Diagnostic Trouble Codes), Powertrain Codes.

Because do not include NHTSA complaint data for P0718, probability estimates below are and typical repair scenarios for intermittent sensor/signals in transmission speed sensor circuits. Use these as plausible guidelines rather than statistically precise values.

• 40-60%: Intermittent turbine/input speed sensor itself or the sensor's immediate electrical relationship
  • Symptoms align with a sensor that occasionally loses signal or has sporadic output.
  • Common root issues include the sensor deteriorating with age, misalignment, or a failing reluctor/signal-generating wheel near the sensor.
• 25-40%: Wiring harness/connector issue
  • Damaged, chafed, corroded, orLoose/poorly seated connectors on the turbine speed sensor circuit (signal, reference, and/or ground wires).
  • Short to ground or intermittent open circuits can produce sporadic sensor readings that trigger P0718.
• 5-15%: PCM/ECM-related fault or software issue
  • Infrequent, intermittent PCM interpretation or a rare software/firmware mismatch can cause a misinterpretation of a valid sensor signal as intermittent.
• 5-10%: Mechanical/reluctor-ring or sensor mounting issue
  • Misalignment, damaged reluctor ring, excessive clearance, or mounting hardware movement can produce inconsistent sensor signals intermittently.
• Other lesser causes (less common, but possible): wiring impedance changes due to temperature, electromagnetic interference, or contamination (oil/connector corrosion) affecting signal integrity.

Important Notes

• Intermittent signals are particularly tricky because a fault may not be present on every ignition/run cycle. This makes live data review and road testing critical to catching the issue when it occurs. The sources describe DTCs as indicators of fault conditions that require confirmation via data and inspection, rather than assumptions based solely on the code.

Diagnostic Approach

1) Verify the DTC and gather context

• Use a capable scan tool to confirm P0718 is active or stored.
• Check freeze frame data and any related codes (e.g., P0715, P0716 if present) to see under what conditions the fault occurred (speed, gear, load, temperature). This helps correlate with possible sensor operation.

2) Inspect basic mechanical and electrical components

• Visually inspect the turbine/input speed sensor and its wiring:
  • Look for damaged, pinched, chafed, or exposed wires along the harness.
  • Check the sensor mounting for proper alignment and secure mounting.
  • Inspect electrical connectors for corrosion, bent pins, and proper locking engagement.
• Check the sensor ground and power supply:
  • Confirm there is a solid ground path to the sensor housing and that the reference voltage (often 5V) is present at the sensor input circuit.

3) Inspect the reluctor ring and sensor alignment (mechanical side)

• If a reluctor ring or tone wheel is used with the turbine/input speed sensor, inspect for damage, misalignment, or debris that could intermittently alter the signal.
• Confirm the sensor is centered on the reluctor ring and not shifted due to mounting hardware wear.

4) Perform live data testing with a scan tool

• Monitor real-time turbine/input speed sensor data (often labeled as Input/Turbine Speed Sensor, Transmission Input Speed, or similar) while varying driving conditions (idle, light throttle, acceleration, warm-up, and steady speeds).
• Look for intermittent dropouts, sudden zero readings, or readings that jump erratically while vehicle speed changes. Record any correlation with gear changes, RPM, load, or temperature.
• Compare the turbine speed signal to vehicle speed (if the data set provides vehicle speed or if you can observe a ratio to engine RPM). A mismatch or inconsistent correlation suggests signal integrity issues.

5) Electrical diagnostics

• With the ignition ON (engine off or cranking per vehicle procedure), perform resistance/continuity checks on the sensor circuit:
  • Check the sensor's signal wire for continuity to the ECM/TCM input pin.
  • Check the reference voltage wire and the sensor ground wire for continuity to ground.
  • Check for unwanted shorts to power, to ground, or to other circuits.
• Inspect the connector pins for corrosion, bent pins, or signs of moisture. Re-seat or replace as needed.

6) Perform a scope/waveform check (advanced)

• If available, use an oscilloscope to view the sensor's waveform:
  • A healthy sensor typically shows a clean, regular waveform with stable amplitude corresponding to RPM.
  • Intermittent signal may present as intermittent missing pulses or a waveform that disappears under certain conditions (temperature, vibration, creeping corrosion).

7) Check related transmission components and software

• If wiring and sensor hardware check out, consider PCM/TCM software/flash status and possible known issues for the vehicle model.
• Ensure there are no active service bulletins affecting transmission speed sensing or related control logic.

8) Perform a controlled road test

• Road-test the vehicle under the same conditions that previously elicited the DTC (temperature, throttle demand, and vehicle speed profile).
• Observe whether the DTC reappears and whether live sensor data continues to show intermittent behavior.

9) Confirm repair and re-test

• After performing a repair (sensor replacement, wiring repair, connector replacement, or moisture cleanup), clear the codes.
• Road-test to ensure the fault does not recur and DTC does not return within a reasonable drive cycle.
• Re-scan to verify the P0718 is cleared and that no new related codes appear.

Recommended repair actions (based on likely causes)

• If sensor or reluctor/wiring issue is confirmed:
  • Replace the turbine/input speed sensor and repair any damaged wiring or connectors.
  • Re-seat and clean connectors; replace damaged harness sections as needed.
  • Verify proper sensor alignment and secure mounting.
• If wiring/connectors are the root cause:
  • Repair or replace damaged harness segments and ensure secure connector engagement.
  • Restore proper grounding and reference voltage paths.
• If PCM/ECM software or calibration is implicated:
  • Apply manufacturer-recommended software/ calibration updates or reflash the PCM/ECM after confirming the issue is software-related.
• If mechanical reluctor ring misalignment or damage is found:
  • Repair or replace the reluctor ring or related mounting hardware; ensure correct spacing and alignment with the sensor.

Safety Considerations

• Disconnect the battery before performing electrical harness work or sensor replacement to avoid short circuits.
• When working under the vehicle, use proper jack stands and wheel chocks; do not rely on jacks alone.
• Follow the vehicle's service manual for torque specifications and procedure steps to avoid damaging sensor threads or sensor mounting components.
• If the transmission is known to run hot or if the vehicle has a known issue with transmission fluid contamination, address those conditions first, as heat and contamination can contribute to intermittent electrical signal behavior.

Documentation and cross-checks

• Document all findings, including:
  • Exact DTC code, date/time, and the observed symptoms.
  • Live data observations (sensor readings, vehicle speed, RPM) and any correlation with conditions.
  • Visual inspection results and wiring/mechanical condition.
  • Repair steps performed and parts replaced.
• Re-scan after repair to confirm the fault is cleared and no new codes appear.

How to discuss P0718 with the customer

• Explain that P0718 indicates an intermittent problem with the turbine/input speed sensor circuit, which can affect transmission behavior, shifting, and performance.
• Emphasize that intermittent faults can be caused by sensor wear, wiring/connectors, or mounting issues, and that a careful inspection and targeted diagnostic testing is needed to identify the root cause.
• Outline the recommended plan (inspection of sensor and harness, live data checks, potential sensor replacement, possible wiring repairs, and a road test) and provide an estimated repair timeline and cost range after initial inspection.

This diagnostic guide was generated using verified reference data:

• Wikipedia Technical Articles: OBD-II
• Open-Source OBD2 Data: N/A (MIT)

Content synthesized from these sources to provide accurate, real-world diagnostic guidance.

---