P0715 Code: Input/Turbine Speed Sensor Circuit Malfunction

A P0715 code means the TCM is not getting a valid signal from the input speed sensor — also called the turbine speed sensor. This sensor reads the rotational speed of the transmission input shaft, which spins at the same speed as the torque converter turbine. Without this signal, the TCM is flying blind. It cannot calculate gear ratios, control shift timing, or manage torque converter lockup.

When the TCM loses the input speed signal, expect harsh shifting, delayed engagement, or the transmission going into limp mode (stuck in one gear). You will almost always see a P0700 stored in the PCM alongside this code.

How the Input Speed Sensor Works

The input speed sensor is typically a magnetic pickup — either a permanent magnet type (variable reluctance) or a Hall effect type. It sits in the transmission case, positioned near a toothed reluctor ring on the input shaft.

Permanent Magnet (Variable Reluctance) Sensors

These generate their own AC voltage signal as the reluctor teeth pass by the sensor tip. The faster the shaft spins, the higher the voltage and frequency. Typical output is 0.5–2V AC at idle and increases with speed. These sensors have two wires — signal and ground/return.

Hall Effect Sensors

These require a power supply (usually 5V or 12V) and produce a clean digital square wave output. They are more accurate at low speeds but have three wires — power, ground, and signal. A bad power supply or ground will kill the signal completely.

The TCM uses the input speed signal combined with the output speed sensor signal to calculate the actual gear ratio in real time. If input speed reads 2,400 RPM and output speed reads 800 RPM, the ratio is 3:1 — which should match a specific gear. If the TCM cannot get the input speed signal, it cannot perform this calculation.

Common Causes of P0715

• Failed sensor: The sensor itself wears out. Internal magnet weakens, coil opens, or Hall effect circuit fails. This is the most common cause.
• Damaged wiring: The sensor harness runs from the transmission case to the TCM. It passes through hot, vibrating environments. Wires break internally, insulation melts, or connectors corrode.
• Corroded connector: ATF leaks can wick up the harness and contaminate the electrical connector at the transmission case. The oil degrades the terminal plating and creates resistance.
• Damaged reluctor ring: If teeth on the reluctor are chipped, cracked, or missing, the sensor produces an erratic or incomplete signal. This usually requires internal transmission access to inspect.
• TCM internal fault: Rarely, the input circuit inside the TCM itself fails. Rule everything else out before going here.

Step-by-Step P0715 Diagnosis

Step 1: Verify the Complaint with Scan Data

Connect a scan tool to the TCM and monitor the input speed PID. With the engine running and the transmission in Drive (wheels off the ground or on a lift), the input speed should closely match engine RPM once the torque converter is turning. If the scan tool shows 0 RPM for input speed while the engine is running in gear, the signal is dead.

Step 2: Locate and Inspect the Sensor

The input speed sensor is mounted on the transmission case — usually on the side or front, near the bellhousing area. Location varies by manufacturer. Consult service info for your specific vehicle. Pull the electrical connector and inspect for corrosion, bent pins, or ATF contamination. Look at the sensor body for physical damage or excessive metallic debris on the tip (some metallic fuzz is normal, a chunk of metal is not).

Step 3: Test the Sensor — Variable Reluctance Type

With the sensor unplugged, measure resistance across the two terminals with your DVOM. Most variable reluctance sensors spec at 200–2,000 ohms. An open reading (OL) means the internal coil is broken. A shorted reading (near 0 ohms) means the coil windings are touching. Compare to manufacturer spec.

For a dynamic test, put the DVOM on AC volts. With the sensor plugged in and backprobed, have someone put the transmission in gear on a lift. You should see an AC voltage that increases with speed — at least 0.3–0.5V AC at low speed.

Step 4: Test the Sensor — Hall Effect Type

With the connector unplugged, turn the key on (engine off). Check for reference voltage at the harness connector — you should see 5V or 12V on the supply pin and good ground on the ground pin. If power and ground are present, reconnect the sensor and backprobe the signal wire. With the transmission spinning, you should see a clean square wave toggling between near 0V and the reference voltage. A scope makes this test much easier than a multimeter.

Step 5: Check the Wiring

With the sensor and TCM unplugged, check continuity on each wire from the sensor connector to the TCM connector. You should see less than 2 ohms on each wire. Also check for shorts to ground and shorts between the wires — each wire should read OL to ground and OL to the other wires.

Step 6: Inspect the Reluctor Ring

If the sensor, wiring, and connectors all check good, the reluctor ring may be damaged. On some transmissions, you can see it through the sensor bore with a borescope. On others, you need to pull the valve body or disassemble the transmission. Look for cracked, chipped, or missing teeth.

Common Diagnostic Mistakes

• Replacing the sensor without checking the connector. A corroded connector will kill the signal from a brand-new sensor just as fast as the old one.
• Not checking for ATF contamination in the harness. Transmission fluid wicks up inside the wire insulation through capillary action. A sensor connector can look clean on the outside while the wires are saturated with ATF internally. This is common on Chrysler and Honda transmissions.
• Confusing the input and output speed sensors. They often look identical and are close together on the transmission case. Make sure you are testing and replacing the right one. Input speed sensor reads the turbine/input shaft. Output speed sensor reads the output shaft.
• Not verifying with scan data after replacement. Always confirm the new sensor is producing a valid signal on the scan tool before calling it done.

Confirming the Repair

Clear TCM and PCM codes. With the scan tool connected, road test the vehicle through all gears. Monitor input speed, output speed, and commanded vs. actual gear ratio. The input speed signal should be smooth and proportional to engine RPM. Shifts should be crisp and on time. No codes should return after two complete drive cycles.

If you have both input and output speed sensor codes, start with the one that is easier to access and test — often the fix for one resolves the other if it was a shared connector or harness issue.