P0718 Input/Turbine Speed Sensor "A" Circuit Intermittent

The P0718 – Input/Turbine Speed Sensor "A" Circuit Intermittent diagnostic trouble code (DTC) indicates that the transmission control module (TCM) has detected an intermittent problem with the signal from Input/Turbine Speed Sensor "A".

This sensor monitors the rotational speed of the transmission input shaft, also commonly called the turbine shaft. The TCM uses this information to determine how fast power is entering the transmission and to coordinate gear changes, calculate transmission ratios, monitor clutch slip, and control the torque converter.

The important word in P0718 is “Intermittent.” The sensor may work correctly most of the time, but its signal occasionally disappears, becomes erratic, or falls outside the expected pattern.

What Does P0718 Mean?

In simple terms:

The TCM is receiving a signal from Input/Turbine Speed Sensor "A", but the signal intermittently becomes unreliable.

The basic process is:

Engine/transmission input rotates → Input speed sensor detects rotation → Sensor sends signal → TCM monitors the signal → Signal intermittently becomes abnormal → P0718 is stored

This is different from a complete sensor failure. An intermittent fault can be particularly difficult to diagnose because the vehicle may operate normally during a workshop inspection.

What Is the Input/Turbine Speed Sensor?

The Input/Turbine Speed Sensor (TSS) measures the rotational speed of the transmission input or turbine shaft.

Depending on the transmission design, it may monitor:

• Transmission input shaft speed

• Torque converter turbine speed

• A rotating reluctor or tone wheel

The TCM compares this information with other signals, especially:

• Engine RPM

• Output shaft speed

• Vehicle speed

• Selected gear

• Throttle position

This allows the controller to determine whether the transmission is behaving as expected.

Why Is Input Speed Important?

The TCM needs to know how quickly power is entering the transmission.

Input-speed information helps it:

• Control shift timing

• Calculate gear ratios

• Monitor clutch slip

• Control torque converter operation

• Detect abnormal transmission behavior

• Coordinate pressure commands

• Determine whether the commanded gear has actually engaged

If the input-speed signal intermittently becomes unreliable, the TCM may temporarily lose an important reference point.

Symptoms of P0718

Symptoms vary depending on the vehicle and severity of the signal interruption.

Possible symptoms include:

Erratic shifting

The transmission may shift unpredictably.

Harsh shifting

Gear changes may become harder than normal.

Delayed shifting

The transmission may hesitate before changing gears.

Transmission slipping

The TCM may have difficulty determining actual transmission slip.

Incorrect gear selection

The controller may select a gear that does not match the driving conditions.

Engine RPM fluctuations

Incorrect input-speed information can affect transmission control.

Torque converter clutch problems

TCC engagement or release may become abnormal.

Limp mode

The transmission may enter a protective operating strategy.

Incorrect gear-ratio codes

P0718 can sometimes be accompanied by gear-ratio DTCs.

Check Engine Light

The malfunction indicator lamp may illuminate.

What Causes P0718?

Several faults can cause an intermittent input-speed signal.

Failing Input/Turbine Speed Sensor

The sensor may be internally failing and intermittently losing its signal.

Damaged wiring

A partially broken wire can work normally until vibration or movement causes the connection to fail.

Loose connector

Poor terminal contact can interrupt the signal.

Corroded terminals

Corrosion can increase resistance and cause signal loss.

Water or oil intrusion

Contamination can interfere with the electrical connection.

Damaged reluctor or tone ring

The sensor may not be able to correctly read the rotating target.

Incorrect sensor installation

An incorrect sensor position or air gap can create an unstable signal.

Metal debris

Magnetic sensors can be affected by excessive metallic contamination.

Internal transmission wiring problem

Some transmissions locate the speed sensor and its wiring inside the transmission.

Power or ground problem

A sensor may intermittently lose its required electrical supply or ground.

TCM wiring problem

The sensor signal can be interrupted between the transmission and TCM.

CAN communication problem

On some vehicles, speed information is exchanged electronically between control modules.

TCM fault

A control-module problem is possible, but it should normally be considered after the sensor and circuit have been properly tested.

Can a Bad Input Speed Sensor Cause P0718?

Yes.

The Input/Turbine Speed Sensor is one of the primary components to inspect.

An aging sensor can operate normally when the vehicle is cold and then begin losing its signal as temperature rises.

It may also fail only:

• At a particular RPM

• In a particular gear

• During acceleration

• During deceleration

• Under heavy vibration

This is why an intermittent sensor fault can be difficult to reproduce.

Can Wiring Cause P0718?

Yes, and wiring should be taken seriously with an intermittent code.

A wire can have good continuity while the vehicle is stationary but lose electrical contact while driving.

Inspect for:

• Broken conductors

• Chafed insulation

• Loose terminals

• Corrosion

• Poor connector locking

• Wiring stretched around the transmission

• Harness contact with hot components

A wiggle test can sometimes reproduce an intermittent fault, but testing should be performed carefully and according to the manufacturer's procedures.

Can a Connector Cause P0718?

Yes.

A loose or corroded connector can cause the input-speed signal to intermittently disappear.

Inspect for:

• Bent pins

• Loose terminals

• Corrosion

• Moisture

• Oil contamination

• Damaged locking tabs

A connector does not need to be completely disconnected to cause P0718.

Even a small change in terminal contact can interrupt a sensitive sensor signal.

Can a Damaged Reluctor Cause P0718?

Yes.

The Input/Turbine Speed Sensor generally reads a rotating target.

If the reluctor or tone ring is damaged, the signal can become irregular.

Possible problems include:

• Damaged teeth

• Cracks

• Deformation

• Misalignment

• Excessive runout

• Incorrect installation

This can produce an intermittent signal even when the sensor itself is functioning.

Can Transmission Fluid Cause P0718?

Usually not directly.

However, contaminated transmission fluid can sometimes contribute to sensor problems.

If the sensor is magnetic, metal particles may accumulate around it and interfere with signal generation.

More importantly, excessive metal debris in the transmission fluid can indicate internal wear.

Therefore, fluid condition can provide an important diagnostic clue, but replacing transmission fluid alone should not be considered a guaranteed repair for P0718.

Can a Bad Ground Cause P0718?

Yes.

A poor ground can cause an unstable sensor signal.

Check:

• Sensor ground

• Transmission ground

• Engine ground straps

• TCM ground

• Battery negative connections

Voltage-drop testing can be useful for identifying a ground that appears acceptable at rest but becomes problematic under operating conditions.

Can Low Voltage Cause P0718?

Potentially.

An unstable electrical supply can interfere with sensor and control-module operation.

If P0718 appears together with multiple unrelated electrical codes, inspect:

• Battery voltage

• Alternator output

• Battery terminals

• Engine grounds

• Transmission grounds

• Module power supplies

However, low battery voltage should not automatically be assumed to be the cause.

Can P0718 Cause Incorrect Gear-Ratio Codes?

Yes.

This is an important relationship.

The TCM uses input speed and output speed to calculate the actual transmission ratio.

If the input-speed signal intermittently becomes incorrect, the controller may calculate an incorrect ratio.

P0718 may therefore appear together with codes such as:

• P0729 – Gear 6 Incorrect Ratio

• P0730 – Incorrect Gear Ratio

• P0731 – Gear 1 Incorrect Ratio

• P0732 – Gear 2 Incorrect Ratio

• P0733 – Gear 3 Incorrect Ratio

• P0734 – Gear 4 Incorrect Ratio

When P0718 appears alongside several ratio codes, the input-speed signal should be verified before assuming that multiple internal transmission components have failed.

Can P0718 Cause Transmission Slipping?

It can create symptoms that feel like slipping.

The TCM uses input speed to determine the relationship between engine speed and transmission operation.

If the sensor signal suddenly becomes incorrect, the controller may not be able to accurately calculate clutch slip.

The resulting behavior may feel like:

• RPM flare

• Delayed engagement

• Abnormal shifting

• Temporary loss of drive

This does not automatically mean the internal transmission clutches are worn.

Can P0718 Affect the Torque Converter?

Yes.

The input/turbine speed signal is closely related to torque converter operation.

The TCM can use turbine speed to monitor the relationship between:

Engine speed ↔ Turbine speed ↔ Transmission input/output speed

If the turbine-speed signal becomes unreliable, torque converter clutch control may be affected.

Possible symptoms include:

• Incorrect TCC engagement

• Incorrect TCC release

• RPM fluctuations

• Reduced fuel economy

• Unusual cruising behavior

Can P0718 Cause Limp Mode?

Yes, it can.

If the TCM cannot reliably determine transmission input speed, it may activate a protective strategy.

Possible results include:

• Fixed-gear operation

• Limited gear selection

• Harsh shifts

• Disabled torque converter clutch

• Reduced transmission functionality

The exact response varies by transmission.

How Is P0718 Diagnosed?

Because P0718 is an intermittent code, diagnosis should focus on determining when the input-speed signal becomes unreliable.

1. Scan all DTCs

Look for additional codes involving:

• Input speed

• Output speed

• Engine speed

• Gear ratios

• Torque converter clutch

• Transmission pressure

• CAN communication

2. Check freeze-frame data

Look at:

• Engine RPM

• Input/turbine RPM

• Output speed

• Vehicle speed

• Selected gear

• Transmission temperature

• Throttle position

The conditions under which the fault occurred can be extremely useful.

3. Monitor input-speed live data

Watch the turbine/input speed while driving.

Look for:

• Sudden drops

• Sudden spikes

• Implausible RPM

• Signal interruptions

• Input speed that does not correspond to engine and transmission operation

4. Compare engine speed and turbine speed

The relationship between engine RPM and turbine speed should make sense for the operating condition.

An unexplained sudden change can indicate a sensor or signal problem.

5. Inspect the sensor

Check the sensor's condition, mounting, and contamination.

6. Inspect the connector

Look for corrosion, loose terminals, bent pins, and contamination.

7. Test the wiring

Check for:

• Open circuits

• Shorts

• Excessive resistance

• Poor terminal contact

8. Check power and ground

Verify the sensor receives the correct supply and ground.

9. Inspect the reluctor

If the electrical circuit is correct, inspect the mechanical target.

10. Road test under the conditions that trigger the code

If P0718 occurs only at a particular temperature, RPM, gear, or load, reproduce those conditions.

Why Is Live Data Important for P0718?

Live data is especially valuable because the problem may disappear when the vehicle is stationary.

For example:

Engine RPM: 2,500 RPM → Input speed: normal

Then during acceleration:

Engine RPM: 2,800 RPM → Input speed: suddenly drops to an implausible value

If the signal immediately returns to normal, an intermittent sensor, connector, or wiring problem becomes a strong possibility.

What If P0718 Appears Only When the Transmission Is Hot?

This is a useful clue.

A sensor may work perfectly when cold and fail once it reaches operating temperature.

Possible causes include:

• Internal sensor failure

• Heat-sensitive wiring

• Connector expansion

• Internal transmission wiring problems

The vehicle should therefore be tested at operating temperature rather than only immediately after startup.

What If P0718 Appears During Acceleration?

Acceleration creates increased load and movement around the transmission.

If P0718 appears during hard acceleration, inspect:

• Sensor wiring

• Connector

• Harness routing

• Transmission grounds

• Sensor mounting

A damaged wire may lose contact as the transmission moves under load.

What If P0718 Appears at a Specific RPM?

A speed-specific failure can point toward the sensor or reluctor.

If the code repeatedly appears around a particular RPM, investigate:

• Sensor waveform

• Reluctor condition

• Sensor air gap

• Wiring vibration

• Electrical interference

An oscilloscope can be particularly helpful in this situation.

Can an Oscilloscope Diagnose P0718?

Yes.

An oscilloscope can capture the actual sensor waveform while the transmission is operating.

It can reveal:

• Missing pulses

• Irregular pulses

• Distorted waveform

• Electrical noise

• Signal dropouts

• Incorrect frequency

This is particularly valuable for intermittent faults that cannot be reproduced with a simple resistance test.

Is P0718 a Serious Problem?

It can become serious if ignored.

The input-speed signal is an important reference for transmission control.

Continued operation with an unreliable signal may cause:

• Harsh shifting

• Incorrect gear selection

• Transmission slip-like symptoms

• Torque converter problems

• Limp mode

• Incorrect gear-ratio calculations

The seriousness depends on how frequently the signal is lost and how the transmission responds.

Can You Drive With P0718?

If the transmission continues to operate normally, a short drive to a repair facility may be possible.

However, continued driving is not recommended if you experience:

• Severe shifting

• Transmission slipping

• Unexpected gear changes

• Limp mode

• Strong RPM fluctuations

• Significant loss of transmission performance

An intermittent input-speed signal can cause unpredictable transmission behavior.

How Is P0718 Repaired?

The correct repair depends on the confirmed cause.

Possible repairs include:

• Replacing the Input/Turbine Speed Sensor

• Repairing damaged wiring

• Repairing connector terminals

• Correcting sensor installation

• Repairing power or ground problems

• Repairing internal transmission wiring

• Repairing or replacing a damaged reluctor

• Correcting communication faults

• Replacing the TCM only when properly diagnosed

The sensor should not automatically be replaced simply because P0718 is stored.

Does P0718 Require Transmission Repair?

Not necessarily.

P0718 is an intermittent sensor-circuit code.

A faulty sensor, connector, wiring problem, or electrical connection can cause it without any internal transmission failure.

If the sensor is integrated into the transmission's internal assembly, additional labor may be necessary, but that still does not mean the transmission needs rebuilding.

Common Diagnostic Mistakes

Assuming the transmission is mechanically damaged

P0718 does not automatically indicate internal transmission failure.

Replacing the sensor without checking the wiring

An intermittent wiring fault can produce exactly the same code.

Testing only when the vehicle is cold

The fault may occur only at operating temperature.

Ignoring the connector

Poor terminal contact is a common cause of intermittent signals.

Ignoring live data

The actual signal behavior is often more informative than a static resistance measurement.

Ignoring related ratio codes

Incorrect input speed can create secondary gear-ratio codes.

Replacing the TCM too quickly

The sensor circuit should be thoroughly tested before condemning the control module.

How Do You Clear P0718?

The underlying problem should be repaired first.

After the repair:

Clear the DTC → Monitor input/turbine speed live data → Road test → Reproduce normal operating conditions → Rescan

The input-speed signal should remain stable and correspond logically with engine speed and transmission operation.

If P0718 returns, the intermittent fault has not been fully resolved.

Final Thoughts on P0718

P0718 – Input/Turbine Speed Sensor "A" Circuit Intermittent means that the TCM has detected an intermittent problem with the input/turbine speed signal.

Unlike a complete no-signal condition, P0718 means the sensor signal may work normally for a period and then suddenly become unreliable.

The most important areas to investigate are the Input/Turbine Speed Sensor, connector, wiring, power supply, ground, internal transmission wiring, and the reluctor or tone ring.

The intermittent nature of the fault is especially important. A vehicle can drive normally during a short workshop test and still have a serious signal problem under specific conditions such as high transmission temperature, hard acceleration, vibration, a particular gear, or a particular RPM.

P0718 can also create secondary transmission codes because the TCM uses input speed to calculate gear ratios and monitor transmission slip. Therefore, if P0718 appears together with several gear-ratio codes, the input-speed signal should be verified before assuming that the transmission has multiple mechanical failures.

A practical diagnostic path is:

Scan all DTCs → Check freeze-frame data → Monitor input/turbine speed live data → Compare input speed with engine RPM and output speed → Inspect the sensor → Check connector and terminals → Test wiring → Verify power and ground → Inspect the reluctor/tone ring → Test the signal waveform if necessary → Reproduce the fault under real driving conditions → Repair the confirmed cause → Clear the code → Road test and rescan.

Most importantly, P0718 does not automatically mean that the transmission needs to be rebuilt. A faulty sensor or a relatively simple wiring or connector problem can be enough to trigger this code.